Dave, you saved another GX270 !!! Mine!!! The same speed problem so I went directly to the TIP48 and found out the same situation. Used an isolation kit from another tranzistor so in 5 minutes it was fixed. Thank you for sharing your knowledge and experience with us. Thumbs UP !!!
I definitely enjoy your videos if I lived a lot closer to you I would have some work for you I live in Marion Illinois and there is nobody that works on stereo equipment in this area and I hate it I have such a passion for vintage audio
There is a reason people come to me from a long way out to get stuff fixed. The guy that owned this is over 50 miles away. That is 100 miles round trip and he brings me a few things. I have several regular customers, most are in the buying and reselling business that have me look at their stuff and get it working. Most want just the minimum done so they can maximize their profits which is fine by me. Some buy stuff for themselves and keep it till a better piece is found and then sell it. That is what I need to do, sell off the excess inventory I own, that I have fixed but will never use like all those cassette decks and turntables I have collected.
@@12voltvids I love watching you cos you explain as you go along with it, how they work how they can go wrong I've managed to repair two of my own TVs from you, caps on one cos they was swollen and back light LEDs and you told us to turn the back light down to help them from blowing again, just had new TV first thing I did thank to you no other tell you like you do thanks
I had something like this happen with a 24V 6A switching power supply back in college. I can't remember if it was Phihong or Meanwell, but they forgot to put an insulating bushing on the Schottky rectifier. This connected the secondary of the switching transformer to directly to ground. It made the bench GFCI trip in the breaker room across the hall due to all the EMI. (The PSU itself didn't fault since the output floats unless you intentionally ground it).
Hilarious at approximately 49 minutes 15 seconds ... "I'll bore you guys with the reassembly of this ...." that's the 2nd job you do Dave (comedian) 🤪😁😃 LOL great videos as always
@@nsummy I do hope Dave got a chuckle out of my comment as that is the way I intended LOL. ANYBODY who has done trouble shooting can tell you real quick that can easily take hours, but once the problem is found (especially something as simple as the discovered of manufacturing flaw like that one, the repair happens VERY QUICK. Not to say all trouble shooting takes that long by any means, basic sometimes will reveal a missing voltage 90% of the time that is the exact place Dave checks first (such as the dead display on that VCR think it was a Sony, (is it getting power?) I have a corny sense of humor anyway so in some cases I find comments like "I'll spare you guys the agony of reassembly". He faked getting a shock from the mains going to a power transformer in a cassette deck if memory serves. He commented back and say he faked it. That was VERY funny because I've jolted myself I don't know how many times and to see someone else get jolted (and not feel it) strikes my tickle box pretty hard.
Hi, I had the same problem on my GX-230D and I just had to put a cold spray on TR2 (TIP47) to remove the failure at startup. I changed TR2 by a TIP48, (you can put a TIP 49 or TIP50 instead) and it worked very well afterwards. TR2 heats up a lot because it behaves like a resistor and becomes defective. The failure could only come from this transistor, it took me one hour to find the failure and the replacement, I think you have complicated your life. But it's good you fixed your machine :)
Well done :-D, that was a bugger. I've known mica insulator shorts due to a tiny metal particle, but a missing screw isolator would never be noticed normally. I wonder if there were different versions of the mistake like a fleck of solder in the mica or missing mica. A fault could also exist for years, but the two bottom plate screws were not tight enough to earth the heatsink out, then years later one of them made contact. Time bomb just waiting lol.
As an engineer I had a similar problem on one of my designs. I designed in an MOSFET in TO-220 Fullpack (plastic isolated mounting) but the purchase departement only gets the unisolated TO-220. As they assembled it on a GND heatsink the eloxal layer of the alluminium first provides enough isolation. But sooner or later the MOSFET shortet. As I finally saw what they did I get the problem.
Greetings from Sydney Australia! Enjoy your videos! i have the Akai GX 230D which my dad bought in Sydney in 1978 still in excellent condition. I think the difference between my deck & the 270 was mine has black rubber rotary controls and piano keys in place of the button solenoid ones & I think yours has peak level meters as well. Will be ordering a new pinch roller/ tyre for it soon as the original rubber is hard as a rock.Thanks for showing the acess to the Monitor/Source button as mine is dusty/playing up so will need some Deoxit as well.I have noticed that when i pulled it out the other day to fire up & lacing up some tape I am getting a slight "tingle" when i touch the right brake lever tension arm? I am wondering after watching your video could it be that transistor that had cause all your angst , is now conducting through the heat sink and hence the causing the "tingle"
Google info: Gold Leaf is about 0.5 microns in thickness. In comparison human hair is around 60 microns in thickness. Gold leaf is so thin that when it is held up against light it is possible to see through it.
The control part of the servo circuit acts as a ballast load in series with the motor, connected by means of that bridge rectifier so you can control both polarities of the AC current with a single, positive polarity, which is carried out by the "un-insulated" power transistor. There is no DC current going to the motor coil to slow it down, it's just the voltage drop on the ballast (servo control) getting bigger, hence smaller on the motor.
Yes I explained it wrong in this one. I did a deep dive of the control circuit in a follow up after I re drew the circuit. The dc voltage only shows on the + side of the bridge. The DC voltage change on the collector creates an ac voktage change on the motor winding. I wasn't in an analytical mind set as I was shooting and repairing. Once the video was done I was looking at the schematic and analyzed it. It was the ground referenced emitter and the - side of the bridge that creates the confusion because the motor winding is not grounded. It operates off a separate winding. Had the bridge and emitter been directly connected without the ground connection it would have been much clearer. The only reason they grounded it was for a reference, as if it wasn't grounded then the voltage measurement would have been made across e-c.
@@12voltvids Exactly, and you explained it very well in your other dedicated video. Basically (or ideally), the servo control is an electronically controlled variable resistor, in series with the motor. The bridge rectifier is used to interface a "one-way" load to an AC supply, symmetrically loading both the + and - sides of the waveform. But on the downside it causes a departure from the ideal linear behavior due to the voltage drop on the diodes, potentially inducing extra hum and less constant torque on the motor (flutter). That's why on some professional gear they are using a clean, synthesized sinewave which is power amplified to supply the motor, with the servo controlling the amplitude directly.
I think it would have been better to make the board a plug-in.Solid telephone wires are prone to breakage.I don't think it can be helped if the vinyl is hard and hard.I feel sorry for the manufacturer, but it can be said that it was a cost failure.
That is a bit weird how when it was built at the factory,,,not to properly insulate that transistor in the end. I guess those diodes u had replaced back earlier in the video made no difference. But great how you have it working well as it should,,in the end after fixing that faulty audio record/playback switch. I had found an insulator on the back of a transistor when I was repairing an old car radio unit,,,that had sound and reception troubles caused by years of abuse,,,of dust and cracked dry circuit joints,,,,,from an old farm ford xy falcon work ute going on so many rough roads. As I had found the screws had come loose and it was shorting out the transistor to earth,,,cutting out the sound. Once I had repaired it and cleaned the dust out,,,realigned the slide tuning capacitor circuit to get better station reception on a mechanical push button tuning radio,,,,it worked so well as it should,,,altogether. It was over 20 years ago when I had repaired it for one of my farmer friends,,,b4 he had retired and sold that vehicle to another local farmer friend we know,,,who may still have that vehicle 2day restored as a vintage on club permit scheme.
I'm an old consumer electronics technician that used to struggle with simular type audio. In fact nobody wanted to work on audio equipment in those days. I must have busted a gut laughing when he started to swear at approximately 29 minutes.
Yeah akai made some really bomb proof machines. I still have to start on my 4000D. A little reluctant to start though. But my guess is I better start soon cause parts are getting hard to find.
Akai also used a multi stage servo control circuit in their VTRs in the 1970s. dutchflyingpilot has videos on servicing Akai VTRs, one covers the servo control circuit.
Lovely troubleshooting.... Just one question What is the purpose of those 2 small black screws that are at the bottom front of the VU meters? What is their purpose?
Slow down the video and watch closely at 35:53. You can see the insulating washer falling on the chassis and hiding under the motor. So the insulating washer was there, it was probably cracked and that caused the short. I've seen a lot of those cracked because of overtightened screws and/or aging due to heat.
And there it is! Good spotting that as I didn't see that at normal speed. Yes it must have cracked over the 50 years and caused leakage. OK I take that back about their engineer being incompetent.
@@12voltvids I've watched this with headphones on, and actually heard the washer dropping, then I came back and slowed it down. It might be a good idea to replace the mica sheet as well. If you can find the original insulating washer, and it's not cracked, there might be a hole in the mica, or a tiny metal shaving that punched through it, and now only the heatsink compound covering it insulates the transistor from the heatsink.
There probably was an insulator on the nut side that crumbled away. I thought initially that it was just the paint that was sealing it falling away, but it was probably the remnants of an insulator that melted over the years and shorted. Funny though as the manual doesn't show it.
@@KHzSineWave You have no idea. All the current for the motor goes through it. It is a series shunt . When I fired it up with no heat sink it went into thermal runaway in about 5 seconds and I cut power before it blew up. Was so hot it couldn't be touched.
@@12voltvids Yikes, that's a lotta current. I had a 5v regulator go into thermal runaway due to a bad IC chip in a CD player once, that sucker got hot enough to leave a perfect TO-220 shaped blister on my finger...
@@12voltvids NICE FIND! So, a possibility to keep it from happening again would be to isolate the heat sink from the main chassis? That way when the plastic insulator decided to crumble away it would still be isolated. Might involve drilling either the heat sink, or the main chassis to accommodate a plastic insulator between the two. That would be another option I suppose? NICE FIND!
Wow great troubleshooting and my Akai GX-265d just started doing the same thing! You said something about the TIP48 being able to be replaced with a TIP31 (easier to find). Even though your TIP48 was good can the TIP31 function in the gx-270, 230, 265 as a sub for a TIP48? Wow -thanks again I feel better about fixing mine!
i got a akai gx265d the guy i bought it from said it had intermittent issues i solved that by cleaning the connectors that plug into the boards i figure loose connections or oxidation
Hello first I really enjoy your channel and discover a great deal I however am stumped with an issue I have with my teac a-4010sl reel to reel deck . After a few minutes of being on it will automatically reverse on it's own I am clueless and I am a visual learner if you can show the process to correct the issue and what parts if any I would need I would really appreciate it thank you in advance all the best always
Thumbs down people are your neighbors, they can not mow the lawn or play loud music outside since the weather is too hot so they need another way to annoy you! Love to see your cat roaming around.
You know when you were talking about the VR102101103X cetera. I kept looking at that transistor and asking myself is it missing an insulator. Nah couldn't be.
19:43 No, the DC is not applied to motor coils! The TR2 just shorting the "+" and "-" of bridge rectifier (and act as variable resistor) and bridge rectifier is actually in series with motor coils, this in turn makes variable amplitude AC seen by motor coils, so the speed is adjusted by varying AC voltage applied to motor > by varying rotor slippage. Same principle is used in Revox machines with asynchronous direct drive capstan motor.
I believe I covered that in the deep dive video of the servo. I was looking only at the dc, thinking back to old vcrs that had a magnetic brake on the drum. Once I redrew the schematic it became very clear and I did a follow up.
@@12voltvids Now I have seen follow up video, yes you explained it very well and exactly what I wrote here. Very nice that you did separate video about it, because most people don't understand this control circuit.
Gee the factory realy stuffed up with no transistor insulator ,Not even the factory inspector picked this up. Well spotted by you in ur searching of fault finding.
This was an adventure! I'd be happy too knowing I succeeded. Go celebrate! By the way, I found one of those gold leaf things inside of a new box of tape, the brand was Irish.
commented on the motor 'breakout' video, but I've seen this many times on revox A77 decks, where the transistor that shunts the motor current goes leaky or short.
page 41/53 of the manual (as on HFE) shows the mounting of that TIP-47 with no insulation, not even the mica sheet, & far less anything to keep the bolt-hole of the collector insulated from the chassis. possible they originally fitted an all-plastic device there, or else that part of the chassis wasn't grounded, & someone's grounded the chassis somewhere else, inadvertently introducing the leakage?
As seems from the schematic even is not the right one the two upper in the right corner transistor form a darlington transistor that probably act as on/off power supply switch for the speed controller board.The four diodes form a bridge rectifier with the transistor in the heat sink form a pwm controller for the ac motor.If the power supply that comes from the darlington output is stable then the fault is inside the control that translates the magnetic pulses to voltage,maybe a small electrolytic capacitor around the transistors or all the small signal transistors replaced for a test.
Its not pwm. It is a FG averaging comparator. The fg pickup is rectified and compared to the reference voltage set by the speed controls. This generates the error voltage that drives the output transistor. The bridge rectifies the ac that has already passed through the motor coil. After shooting the video I looked closer. Yes the DC will rise on the collector but that actually reduces the field current through the coil. I actually do go over this on the extra footage I shot for the future patreon release.
At page 39 of the ServiceManual you can actually se the mounting hardware for the transistor. Without any insulating plate (Mica or whatever you call it) or insulation of the screw and nut. But was the QC at the factory so bad that they didn't catch this fault there? Cause this "runaway capstan" must have been common to all units. Amazing.
Dear Sir. Pls kindly to support about my case: AKAI 270D is running too fast , switch 7 1/2 and 3 3/4 no effect , just the same fast speed. If something happen with transistor TIP 48 control speed I wondered, thanks alot
Hola qué alguien me saque de la duda o me aclare cuál es la falla es normal que se calienten tanto los motores de los reels de la akai 630 no se pueden tocar de lo tanto que se calientan saludos de antemano y espero me puedan ayudar
I recently acquired one of these GX-270D and it powers on with the VU meters lit up the capstan spindle starts spinning. Is that spindle supposed to spin when powered o? Also, none of the function buttons (Play, FF, REW etc.) work when pressed. Any ideas on what the issue/s could be? Thanks!
@@pianissimo3577 Partially. I posted to the Tapeheads Forum and someone responded and said that capstan roller is supposed to spin like that. Haven't resolved the controls yet though.
They were in the dumping phase to put the big players, fisher, Marantz, mcintosh ect out of business. This was Japan's way of retaliation for Hiroshima and Nagasaki. Hit the americans back where it hurts. Look at what Panasonic did to Motorola and quasar. What Sony and Hitachi did to curtis Mathis, rca and zenith. There is a good documentary film about panasonjc and their early history. About how they were initially selling TVs in the USA cheaper than in Japan and actually at a loss. The US government placed an embargo so what did they do? The same thing mitsubishi did in Canada. Bought a struggling domestic company (motorola) and started making quasar branded sets in the USA and then Canada using a domestic picture tube, made in USA or Canada, using local workers and shipped the completed chassis over from Japan. They eventually put the panasonic brand on them too. Mitsubishi did that here with electrohome. On canada they had to keep the electrohome name going for 10 years. Gradually they moved the local production to just putting the cabinet together. This was to satisfy the governments. All a master plan to force the big companies into financial insolvency and they them snapped them up for the name and shut the domestic factories and laid off all the workers. People are fast to blame the Chinese for dumping cheap electronics but those of us over 50 remember the exact same thing happening with stuff coming from japan. And yes I do like Japanese electronics. They made some very good products. Not that I didn't like the Canadian and American products, but they were stuck in a rut for many years turning out the same old stuff. 10 models of TV, all the exact same set with slight styling changes, where as the Japanese when you got a new model it was totally new and better then the old one.
Yeah, diagnosing any sort of closed (feedback) loop circuit is huge PITA. Combine that with the wrong schematic, that’s an instant migraine headache there! 🤯
If the transistor had been bad I would have found it quickly as it was literally the first part I tested. You don't expect leakage through the insulator. Had it also shorted it would have been an easy find but it didn't, and only faulted under high voltage presence. Thats what made this one so much of a challenge.
Nah, AKAI would Never have used a TIP47 Texas Instruments transistor in that age equipment. That would have been fitted by some bone head tech in the past, subbing the original JEDEC Japanese transistor, and forgetting the insulating plastic grommet/washer....
Who would have thought it would be a factory induced fault? Dummies. I have found Akai to be helpful in the past, but expensive if you wanted a part! 1 special bulb around $8 back in 1970 something, around '73/74, that was a lot of money back them, but then only Akai had the bulb. If I knew it was going to cost that I wouldn't have asked them to just invoice it. I would have fitted something else, though it was a long very thin bulb for a cassette deck! It was like asking $25 for a bulb now! Plus they had the nerve to charge P&P :-((
I had only 1 experience with Akai service. This was before I got into the service business, and was probably one of the driving factors to learn it. I would have been perhaps 16. Had tinkered in electronics but no formal training at that time. Had built a few heathkits. I was doing volunteer at the local cable TV station, and really wanted a portable VCR and camera. One of the other volunteers on the crew had this Akai 1/4" reel to reel black and white VTR with a camera. Offered to sell it to me for 600.00. Assured me that it worked fine, I just needed to buy a battery. Even brought it to the station, and played a tape, but didn't offer to make a recording. I spent every penny I had to buy that thing. Then ordered the battery for it from Akai for about 100.00. When I got the battery I found that the portable VTR would not work on battery, only plugged into the base unit (that had a 3" TV monitor built in to view the tapes on) Off to Akai it went. Abother 350.00 later they handed me the unit. It worked, for about 2 weeks and then went dead. Back to Akai it went and this time they refused to service it, even though that were happy to take my money 2 weeks earlier. Said they no longer supported it. I left mad, I was out of pocket about 1000 after buying the thing, and the battery and spending all that money. I went back to the guy that sold it to me and he basically said, it worked when I sold it to you, f*&k off. The only time in my life I ever did anything vindictive against anyone was that prick. One day when he was out volunteering with the crew I took the sugar container from the coffee room and emptied it into his gas tank! Justice was served! He never did figure out who did it but I am sure he had a few suspects. (I wasn't the only one at the community station he f*&ked over. In fact one of the other guys warned me about buying it because he bought something from him before and it was junk) Anyway I tore that machine apart and studied it and spent much time and effort trying to get it running, turned out to be one of those composite modules that were encased in epoxy (early attempt to stop competition from seeing what they were doing) had failed and the part was no longer available, so the unit was scrapped. I kept the little TV monitor and camera and used it as a security camera untill it burned out.
@@12voltvids Yeah, buying things like that second hand is always a chance. Should have headed the warning. However, look at the fun you had trying to fix a lost cause.
Dave, you saved another GX270 !!! Mine!!! The same speed problem so I went directly to the TIP48 and found out the same situation. Used an isolation kit from another tranzistor so in 5 minutes it was fixed. Thank you for sharing your knowledge and experience with us. Thumbs UP !!!
Realmente fué la mejor película que he visto en años! Gracias por compartir
Nothing can beat "the Dave" :) Really awesome. Well done! Big thumbs UP! :)
Then what is with all the thumbs down. I swear to God I am going to have a heart attack the first video I see with 0 thumbs down.
And someone said that they were easy machines to work on. I see that everything is jammed packed in there!
Superb impossible fault (almost) finding, well done AKAI, Wow! how many left the factory like this? you deserve a medal for this one!
I literally breathed a sigh of relief when that motor turned at the right speed after you found the insulator was missing.
Good Job Man. I have the exact same problem and now I will take a lot less time to fix it. and my customer will be very happy.
I will never trust that the insulator was put in or replaced again!! Great JoB!
Used to repair copy machines for a while. Discovered Japanese design philosophy: if two screws work, 6 screws better.
Nice find Dave!🎯👍👏👏👏
I definitely enjoy your videos if I lived a lot closer to you I would have some work for you I live in Marion Illinois and there is nobody that works on stereo equipment in this area and I hate it I have such a passion for vintage audio
You're kidding?
I live in Herrin Illinois! Lol
Wow you are only 7 miles away from me!
I'm learning how to work on equipment but, I'm no Dave at all!
What a legend you are A+ repair again no wonder I like to watch your vids
There is a reason people come to me from a long way out to get stuff fixed. The guy that owned this is over 50 miles away. That is 100 miles round trip and he brings me a few things. I have several regular customers, most are in the buying and reselling business that have me look at their stuff and get it working. Most want just the minimum done so they can maximize their profits which is fine by me. Some buy stuff for themselves and keep it till a better piece is found and then sell it. That is what I need to do, sell off the excess inventory I own, that I have fixed but will never use like all those cassette decks and turntables I have collected.
@@12voltvids I love watching you cos you explain as you go along with it, how they work how they can go wrong I've managed to repair two of my own TVs from you, caps on one cos they was swollen and back light LEDs and you told us to turn the back light down to help them from blowing again, just had new TV first thing I did thank to you no other tell you like you do thanks
Great detective work and perseverance!!
I had something like this happen with a 24V 6A switching power supply back in college. I can't remember if it was Phihong or Meanwell, but they forgot to put an insulating bushing on the Schottky rectifier. This connected the secondary of the switching transformer to directly to ground. It made the bench GFCI trip in the breaker room across the hall due to all the EMI. (The PSU itself didn't fault since the output floats unless you intentionally ground it).
great job I always admire your reparations with ful craftmenship
Hilarious at approximately 49 minutes 15 seconds ... "I'll bore you guys with the reassembly of this ...." that's the 2nd job you do Dave (comedian) 🤪😁😃 LOL great videos as always
I like at the beginning when he said this was the shortened version. I took a look at the time and saw it was an hour long!
@@nsummy I do hope Dave got a chuckle out of my comment as that is the way I intended LOL. ANYBODY who has done trouble shooting can tell you real quick that can easily take hours, but once the problem is found (especially something as simple as the discovered of manufacturing flaw like that one, the repair happens VERY QUICK. Not to say all trouble shooting takes that long by any means, basic sometimes will reveal a missing voltage 90% of the time that is the exact place Dave checks first (such as the dead display on that VCR think it was a Sony, (is it getting power?)
I have a corny sense of humor anyway so in some cases I find comments like "I'll spare you guys the agony of reassembly". He faked getting a shock from the mains going to a power transformer in a cassette deck if memory serves. He commented back and say he faked it. That was VERY funny because I've jolted myself I don't know how many times and to see someone else get jolted (and not feel it) strikes my tickle box pretty hard.
WOW!!! This was a HUGE win!!! Great Repair!!!👍🏼😎
WOW ! Bet you felt great when the light bulb went off! Great video.
Hi, I had the same problem on my GX-230D and I just had to put a cold spray on TR2 (TIP47) to remove the failure at startup.
I changed TR2 by a TIP48, (you can put a TIP 49 or TIP50 instead) and it worked very well afterwards. TR2 heats up a lot because it behaves like a resistor and becomes defective. The failure could only come from this transistor, it took me one hour to find the failure and the replacement, I think you have complicated your life. But it's good you fixed your machine :)
Well done :-D, that was a bugger.
I've known mica insulator shorts due to a tiny metal particle, but a missing screw isolator would never be noticed normally.
I wonder if there were different versions of the mistake like a fleck of solder in the mica or missing mica.
A fault could also exist for years, but the two bottom plate screws were not tight enough to earth the heatsink out, then years later one of them made contact.
Time bomb just waiting lol.
You can be very proud on yourself!!
Brilliant! Good work, a very enjoyable video to watch. You at your best. Liked, subscribed and donated. Ray H. UK
As an engineer I had a similar problem on one of my designs. I designed in an MOSFET in TO-220 Fullpack (plastic isolated mounting) but the purchase departement only gets the unisolated TO-220. As they assembled it on a GND heatsink the eloxal layer of the alluminium first provides enough isolation. But sooner or later the MOSFET shortet. As I finally saw what they did I get the problem.
really well thought out and i congratulate you on this more challenging repair
well done,you have done tougher jobs
Years ago yes. Not so much these days.
Greetings from Sydney Australia! Enjoy your videos! i have the Akai GX 230D which my dad bought in Sydney in 1978 still in excellent condition. I think the difference between my deck & the 270 was mine has black rubber rotary controls and piano keys in place of the button solenoid ones & I think yours has peak level meters as well. Will be ordering a new pinch roller/ tyre for it soon as the original rubber is hard as a rock.Thanks for showing the acess to the Monitor/Source button as mine is dusty/playing up so will need some Deoxit as well.I have noticed that when i pulled it out the other day to fire up & lacing up some tape I am getting a slight "tingle" when i touch the right brake lever tension arm? I am wondering after watching your video could it be that transistor that had cause all your angst , is now conducting through the heat sink and hence the causing the "tingle"
Well done mate, what a crazy job.
OMG! When you first played that test tone, it had me proper laughing. lol
Also BASF is a name I haven't seen in a longgg time.
I am a young guy trying to fix my old gpa’s rtr, and will be using this as a disassembly guide;
Probably a little rough for a first project haha
Google info: Gold Leaf is about 0.5 microns in thickness. In comparison human hair is around 60 microns in thickness. Gold leaf is so thin that when it is held up against light it is possible to see through it.
The control part of the servo circuit acts as a ballast load in series with the motor, connected by means of that bridge rectifier so you can control both polarities of the AC current with a single, positive polarity, which is carried out by the "un-insulated" power transistor. There is no DC current going to the motor coil to slow it down, it's just the voltage drop on the ballast (servo control) getting bigger, hence smaller on the motor.
Yes I explained it wrong in this one. I did a deep dive of the control circuit in a follow up after I re drew the circuit. The dc voltage only shows on the + side of the bridge. The DC voltage change on the collector creates an ac voktage change on the motor winding. I wasn't in an analytical mind set as I was shooting and repairing. Once the video was done I was looking at the schematic and analyzed it. It was the ground referenced emitter and the - side of the bridge that creates the confusion because the motor winding is not grounded. It operates off a separate winding. Had the bridge and emitter been directly connected without the ground connection it would have been much clearer. The only reason they grounded it was for a reference, as if it wasn't grounded then the voltage measurement would have been made across e-c.
@@12voltvids Exactly, and you explained it very well in your other dedicated video. Basically (or ideally), the servo control is an electronically controlled variable resistor, in series with the motor. The bridge rectifier is used to interface a "one-way" load to an AC supply, symmetrically loading both the + and - sides of the waveform. But on the downside it causes a departure from the ideal linear behavior due to the voltage drop on the diodes, potentially inducing extra hum and less constant torque on the motor (flutter). That's why on some professional gear they are using a clean, synthesized sinewave which is power amplified to supply the motor, with the servo controlling the amplitude directly.
@@mihaischitcu1917
That is a frequency drive which uses a 3, phase motor with the servo generating the 3 phase drive signal. Used on all vcrs.
Nice to hear Big Wreck towards the end :) Great video.
Big wreck lead singer Ian Thornley sounds exactly like Chris Cornell from audio slave \ Soundgarden.
A lot of Thank´s it´s a great video
I think it would have been better to make the board a plug-in.Solid telephone wires are prone to breakage.I don't think it can be helped if the vinyl is hard and hard.I feel sorry for the manufacturer, but it can be said that it was a cost failure.
Congrats.. Very good.
That is a bit weird how when it was built at the factory,,,not to properly insulate that transistor in the end. I guess those diodes u had replaced back earlier in the video made no difference. But great how you have it working well as it should,,in the end after fixing that faulty audio record/playback switch.
I had found an insulator on the back of a transistor when I was repairing an old car radio unit,,,that had sound and reception troubles caused by years of abuse,,,of dust and cracked dry circuit joints,,,,,from an old farm ford xy falcon work ute going on so many rough roads. As I had found the screws had come loose and it was shorting out the transistor to earth,,,cutting out the sound.
Once I had repaired it and cleaned the dust out,,,realigned the slide tuning capacitor circuit to get better station reception on a mechanical push button tuning radio,,,,it worked so well as it should,,,altogether.
It was over 20 years ago when I had repaired it for one of my farmer friends,,,b4 he had retired and sold that vehicle to another local farmer friend we know,,,who may still have that vehicle 2day restored as a vintage on club permit scheme.
I'm an old consumer electronics technician that used to struggle with simular type audio. In fact nobody wanted to work on audio equipment in those days. I must have busted a gut laughing when he started to swear at approximately 29 minutes.
Yeah akai made some really bomb proof machines. I still have to start on my 4000D.
A little reluctant to start though.
But my guess is I better start soon cause parts are getting hard to find.
Akai also used a multi stage servo control circuit in their VTRs in the 1970s. dutchflyingpilot has videos on servicing Akai VTRs, one covers the servo control circuit.
All vcrs used servo controls for drum and capstan motors
I feel your pain. Have been a technician for over 25 years, always hated Akai. They can be a nightmare to service.
Coming up on 40 years and still not feeling love for akai.
It may have been a wild dog, but you are the Whisperer. In the end, you've tamed it.
Lovely troubleshooting.... Just one question What is the purpose of those 2 small black screws that are at the bottom front of the VU meters? What is their purpose?
Slow down the video and watch closely at 35:53. You can see the insulating washer falling on the chassis and hiding under the motor. So the insulating washer was there, it was probably cracked and that caused the short. I've seen a lot of those cracked because of overtightened screws and/or aging due to heat.
And there it is! Good spotting that as I didn't see that at normal speed. Yes it must have cracked over the 50 years and caused leakage. OK I take that back about their engineer being incompetent.
@@12voltvids I've watched this with headphones on, and actually heard the washer dropping, then I came back and slowed it down. It might be a good idea to replace the mica sheet as well. If you can find the original insulating washer, and it's not cracked, there might be a hole in the mica, or a tiny metal shaving that punched through it, and now only the heatsink compound covering it insulates the transistor from the heatsink.
This unit must've been made on a Monday / Friday. That's one hell of a frick up, once again, nice detective work!
There probably was an insulator on the nut side that crumbled away. I thought initially that it was just the paint that was sealing it falling away, but it was probably the remnants of an insulator that melted over the years and shorted. Funny though as the manual doesn't show it.
@@12voltvids Ah that would make sense I can imagine how hot that transistor must get in operation, strange how the manual doesn't list it.
@@KHzSineWave
You have no idea. All the current for the motor goes through it. It is a series shunt . When I fired it up with no heat sink it went into thermal runaway in about 5 seconds and I cut power before it blew up. Was so hot it couldn't be touched.
@@12voltvids Yikes, that's a lotta current. I had a 5v regulator go into thermal runaway due to a bad IC chip in a CD player once, that sucker got hot enough to leave a perfect TO-220 shaped blister on my finger...
@@12voltvids NICE FIND! So, a possibility to keep it from happening again would be to isolate the heat sink from the main chassis? That way when the plastic insulator decided to crumble away it would still be isolated. Might involve drilling either the heat sink, or the main chassis to accommodate a plastic insulator between the two. That would be another option I suppose? NICE FIND!
Wow great troubleshooting and my Akai GX-265d just started doing the same thing! You said something about the TIP48 being able to be replaced with a TIP31 (easier to find). Even though your TIP48 was good can the TIP31 function in the gx-270, 230, 265 as a sub for a TIP48? Wow -thanks again I feel better about fixing mine!
i got a akai gx265d the guy i bought it from said it had intermittent issues i solved that by cleaning the connectors that plug into the boards i figure loose connections or oxidation
Hello first I really enjoy your channel and discover a great deal I however am stumped with an issue I have with my teac a-4010sl reel to reel deck . After a few minutes of being on it will automatically reverse on it's own I am clueless and I am a visual learner if you can show the process to correct the issue and what parts if any I would need I would really appreciate it thank you in advance all the best always
Thumbs down people are your neighbors, they can not mow the lawn or play loud music outside since the weather is too hot so they need another way to annoy you! Love to see your cat roaming around.
You know when you were talking about the VR102101103X cetera. I kept looking at that transistor and asking myself is it missing an insulator. Nah couldn't be.
19:43 No, the DC is not applied to motor coils! The TR2 just shorting the "+" and "-" of bridge rectifier (and act as variable resistor) and bridge rectifier is actually in series with motor coils, this in turn makes variable amplitude AC seen by motor coils, so the speed is adjusted by varying AC voltage applied to motor > by varying rotor slippage. Same principle is used in Revox machines with asynchronous direct drive capstan motor.
I believe I covered that in the deep dive video of the servo. I was looking only at the dc, thinking back to old vcrs that had a magnetic brake on the drum. Once I redrew the schematic it became very clear and I did a follow up.
@@12voltvids Now I have seen follow up video, yes you explained it very well and exactly what I wrote here. Very nice that you did separate video about it, because most people don't understand this control circuit.
Gee the factory realy stuffed up with no transistor insulator ,Not even the factory inspector picked this up. Well spotted by you in ur searching of fault finding.
This was an adventure! I'd be happy too knowing I succeeded. Go celebrate! By the way, I found one of those gold leaf things inside of a new box of tape, the brand was Irish.
commented on the motor 'breakout' video, but I've seen this many times on revox A77 decks, where the transistor that shunts the motor current goes leaky or short.
page 41/53 of the manual (as on HFE) shows the mounting of that TIP-47 with no insulation, not even the mica sheet, & far less anything to keep the bolt-hole of the collector insulated from the chassis. possible they originally fitted an all-plastic device there, or else that part of the chassis wasn't grounded, & someone's grounded the chassis somewhere else, inadvertently introducing the leakage?
Crap that lasted 50 years! : )
As seems from the schematic even is not the right one the two upper in the right corner transistor form a darlington transistor that probably act as on/off power supply switch for the speed controller board.The four diodes form a bridge rectifier with the transistor in the heat sink form a pwm controller for the ac motor.If the power supply that comes from the darlington output is stable then the fault is inside the control that translates the magnetic pulses to voltage,maybe a small electrolytic capacitor around the transistors or all the small signal transistors replaced for a test.
Its not pwm. It is a FG averaging comparator. The fg pickup is rectified and compared to the reference voltage set by the speed controls. This generates the error voltage that drives the output transistor. The bridge rectifies the ac that has already passed through the motor coil. After shooting the video I looked closer. Yes the DC will rise on the collector but that actually reduces the field current through the coil. I actually do go over this on the extra footage I shot for the future patreon release.
Sir, based on your experience what is the best way to get more ideas in troubleshooting, in home service or in the shop?
At page 39 of the ServiceManual you can actually se the mounting hardware for the transistor.
Without any insulating plate (Mica or whatever you call it) or insulation of the screw and nut.
But was the QC at the factory so bad that they didn't catch this fault there?
Cause this "runaway capstan" must have been common to all units. Amazing.
I am sure there are a bunch of people digging their old akai units out if the closet now trading into them to fix the fault the last tech gave up on.
"Monstrosity"......"They on Drugs." lol ..Wow Bizzare link to Ground...
Dear Sir.
Pls kindly to support about my case: AKAI 270D is running too fast , switch 7 1/2 and 3 3/4 no effect , just the same fast speed. If something happen with transistor TIP 48 control speed I wondered, thanks alot
amazing video.bravo......
Was it Friday or Monday morning when that was built and shipped. Great find with schematic and insulator.
Service manual shows no insulator! What? Was the engineer smoking crack?
Hello, can I find out from which site to get the maps of the devices that you are repairing? Follow the beautiful Watts video from Iraq
the schematic says GX-270D on it... not 370
min 34:23. There seems to be an insulator between the transistor and the heatsink
... but there was none for the screw :(
Hola qué alguien me saque de la duda o me aclare cuál es la falla es normal que se calienten tanto los motores de los reels de la akai 630 no se pueden tocar de lo tanto que se calientan saludos de antemano y espero me puedan ayudar
Good job!
I recently acquired one of these GX-270D and it powers on with the VU meters lit up the capstan spindle starts spinning. Is that spindle supposed to spin when powered o? Also, none of the function buttons (Play, FF, REW etc.) work when pressed. Any ideas on what the issue/s could be? Thanks!
I'm in the exact same boat - ever figure anything out?
@@pianissimo3577 Partially. I posted to the Tapeheads Forum and someone responded and said that capstan roller is supposed to spin like that. Haven't resolved the controls yet though.
Come on 100,000
F... dd! Belts are always better, no matter if it's on tape-recorders or turntables. Albeit for different reasons though.😎😎
To add insult to injury that was built back in the day when the Japanese stereo market dominated the world.
They were in the dumping phase to put the big players, fisher, Marantz, mcintosh ect out of business. This was Japan's way of retaliation for Hiroshima and Nagasaki. Hit the americans back where it hurts. Look at what Panasonic did to Motorola and quasar. What Sony and Hitachi did to curtis Mathis, rca and zenith. There is a good documentary film about panasonjc and their early history. About how they were initially selling TVs in the USA cheaper than in Japan and actually at a loss. The US government placed an embargo so what did they do? The same thing mitsubishi did in Canada. Bought a struggling domestic company (motorola) and started making quasar branded sets in the USA and then Canada using a domestic picture tube, made in USA or Canada, using local workers and shipped the completed chassis over from Japan. They eventually put the panasonic brand on them too. Mitsubishi did that here with electrohome. On canada they had to keep the electrohome name going for 10 years. Gradually they moved the local production to just putting the cabinet together. This was to satisfy the governments. All a master plan to force the big companies into financial insolvency and they them snapped them up for the name and shut the domestic factories and laid off all the workers. People are fast to blame the Chinese for dumping cheap electronics but those of us over 50 remember the exact same thing happening with stuff coming from japan. And yes I do like Japanese electronics. They made some very good products. Not that I didn't like the Canadian and American products, but they were stuck in a rut for many years turning out the same old stuff. 10 models of TV, all the exact same set with slight styling changes, where as the Japanese when you got a new model it was totally new and better then the old one.
Yeah, diagnosing any sort of closed (feedback) loop circuit is huge PITA. Combine that with the wrong schematic, that’s an instant migraine headache there! 🤯
My head still hurts.
If the transistor had been bad I would have found it quickly as it was literally the first part I tested. You don't expect leakage through the insulator. Had it also shorted it would have been an easy find but it didn't, and only faulted under high voltage presence. Thats what made this one so much of a challenge.
Nah, AKAI would Never have used a TIP47 Texas Instruments transistor in that age equipment.
That would have been fitted by some bone head tech in the past, subbing the original JEDEC Japanese transistor, and forgetting the insulating plastic grommet/washer....
Who would have thought it would be a factory induced fault? Dummies. I have found Akai to be helpful in the past, but expensive if you wanted a part! 1 special bulb around $8 back in 1970 something, around '73/74, that was a lot of money back them, but then only Akai had the bulb. If I knew it was going to cost that I wouldn't have asked them to just invoice it. I would have fitted something else, though it was a long very thin bulb for a cassette deck! It was like asking $25 for a bulb now! Plus they had the nerve to charge P&P :-((
I had only 1 experience with Akai service. This was before I got into the service business, and was probably one of the driving factors to learn it. I would have been perhaps 16. Had tinkered in electronics but no formal training at that time. Had built a few heathkits. I was doing volunteer at the local cable TV station, and really wanted a portable VCR and camera. One of the other volunteers on the crew had this Akai 1/4" reel to reel black and white VTR with a camera. Offered to sell it to me for 600.00. Assured me that it worked fine, I just needed to buy a battery. Even brought it to the station, and played a tape, but didn't offer to make a recording. I spent every penny I had to buy that thing. Then ordered the battery for it from Akai for about 100.00. When I got the battery I found that the portable VTR would not work on battery, only plugged into the base unit (that had a 3" TV monitor built in to view the tapes on)
Off to Akai it went. Abother 350.00 later they handed me the unit. It worked, for about 2 weeks and then went dead. Back to Akai it went and this time they refused to service it, even though that were happy to take my money 2 weeks earlier. Said they no longer supported it.
I left mad, I was out of pocket about 1000 after buying the thing, and the battery and spending all that money. I went back to the guy that sold it to me and he basically said, it worked when I sold it to you, f*&k off.
The only time in my life I ever did anything vindictive against anyone was that prick. One day when he was out volunteering with the crew I took the sugar container from the coffee room and emptied it into his gas tank! Justice was served! He never did figure out who did it but I am sure he had a few suspects. (I wasn't the only one at the community station he f*&ked over. In fact one of the other guys warned me about buying it because he bought something from him before and it was junk)
Anyway I tore that machine apart and studied it and spent much time and effort trying to get it running, turned out to be one of those composite modules that were encased in epoxy (early attempt to stop competition from seeing what they were doing) had failed and the part was no longer available, so the unit was scrapped. I kept the little TV monitor and camera and used it as a security camera untill it burned out.
@@12voltvids Yeah, buying things like that second hand is always a chance. Should have headed the warning. However, look at the fun you had trying to fix a lost cause.
You think this is hard to understand the svc manual, try a Revox where 1/2 of the references are incorrect !
Sorry, JISC not JEDEC....
I will stick with my Teac's , What a mess you got there
Wow...just....WOW.....smh!!!!
Akai equipment was always regarded as cheap rubbish in Australia. No serious music lover would have been seen dead buying Akai.
Remember the pot metal came that just crumbled on the mechanical controls.
I ahve had pretty good luck with the 3 AKAI R-R decks I have.