Broken Amp? NAD a problem! - 'Fixing' A Mid 1980's Amplifier
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- Опубликовано: 29 окт 2022
- May have bit off more than I can chew with this one, it has a lot more talking than any of my prior videos and a lot of electronic troubleshooting, so if that's not your thing feel free to click away.
Otherwise, I learned a great deal about receivers and amplifiers taking this apart and getting it play music again; so, I hope you enjoy and maybe learn something as well. 
Хобби
Thanks for all of the great suggestions! I took your advice and measured the output offset voltage; the right channel I was able to adjust with some pots to be .5mV, while the left channel was measuring 1.5V, so that explains why the relay was tripping and means there is certainly something wrong with the left channel, now to just try and find out what....
Update: Did some more troubleshooting and traced the issue to one of the power transistors that had shorted, I thought that I had checked it but either I forgot or I didn't test it correctly haha. I have ordered a replacement for that transistor, and I have also switched the resistors back to the original 56Kohm reading. Thanks for all the great advice and comments!
Although in idle mode it shouldn't make much difference,
Remove the jumbers from both channels and check again the voltage there.
Then switch it off let it cool and check immediately after powering.
If it starts climbing check with your hand what component is getting warm
Usually a resistor which can drag a transistor by affecting it's bias.
The opposite could happen also.
Lastly, a scope would be really handy now.
Good luck!
Check those distortion trimmers. You will never get offset right if they are oxidized.
R618 should be clearly visible on the left channel side of the amp board. R668 is pretty well hidden under the input selector (silver) extension arm. If these are truly absent and not replaced with 100 ohm resistors, you have a gap in the circuitry. My 7250pe has a build date of 1986 for reference. Someone may have been in your amp. My protection relay was fully sealed and did not have a pop off top like yours. I replaced mine too. But the sealed one I took out matched the listed part number from the service manual omron makes an exact drop in for that relay, although it is not environmentally sealed. Pretty sure I can see the edge of r668 when I pause your video. You seem to be able to get close on the right adjustment, but are way off on the left. I bet they pulled r618 and could not find r668
Thanks for the video, interesting stuff and admitting when you made a simple error, just the sort of mistake I would make. Regards Mike🇬🇧
those relays can go bad as well, i've had to replace two or three omron relays in amps. they get dirty after awhile because of all of the arcing going on inside and they build up carbon and then fail. sometimes parts of them can fuse together. if i'm doing a complete refurb, i would always replace them, and also the voltage offset pots with sealed units
The reason there are so many power transistors is because of the Power Envelope technology. You've got 2 separate output rails (Hi/Low), 2 sets of filter capacitors and commutating diodes that switch into high power (Power Envelope) mode for burst current. Those amps are beasts.
Thanks for the info, it stood out to me because the only other receiver I've opened up had only 4 of them in it haha
Also the higher the operating voltage, the less current the device can supply - SOA. Bigger amps could employ 10 or even more pairs of output transistors. Take a look at Accuphase, or any real high current Hi-End amp capable of driving 2 ohm complex load, which isn't that unusual with 4-6ohm nominal impedance rating. For 100W/8ohm high current A/B class amp is a rule that they need at least 2pairs of 15A/200V, 150W min transistors.
As with many amps from the past century, yeah, there's the U jumper trick in the back - you idiots. Been there done that ;)
I like how you call the thing with a "this is not a handle" sticker on it a handle.
That thing that is labeled "This is not a handle" is the AM rod antenna. Too much pressure/tension on it could break the ferrite core, making the antenna not tune the entire AM band properly.
It picked up edge of seventeen 😊
That receiver look familiar, I was dropping off some donations at Goodwill and spotted a NAD receiver in the electronics department. It was a very dirty and the combo volume/balance knob was stuck. Gave it a good cleaning and TLC and it works great! I left the $12 price tag on it.
I have a NAD receiver that was given to me as broken and the only thing that was wrong was the preamp output was never connected to main input with RCA cables. These are great receivers that have awesome sound and power output.
My favorite repair channel, you sound like a friendly person who likes his work!
Thanks! Glad you enjoyed
The fact that you can make use of whatever you have learned so far,
proves that you're definetely a technician.
Btw those bridges between preamp and amp always make troubleshooting so much easier.
Also on a later stage when the unit is fixed, you can improvise like, driving this amp with another pre-amp
and vise versa.
I had a similar experience on an amp I recently acquired. There are several small value resistors in the amp power rails (the ones marked with the triangles on the schematic). They act as safety "fuses" in the amp power rails. On the amp I was working on, they were supposed to be 120 ohms, but they weren't. Some were outright open, and others had changed values to much higher resistance. Check those really low resistors (I think here they are are like 68 ohms) and see if any have drifted. This will not allow the protect IC to do it's thing. The amp might still run if the protect is defeated, but it's not right.
If anyone considers my fix to be 'spooky', do know this will be a part of my Halloween decorations.
The in/out jumpers are for installing external amps or an equalizer. I noticed as soon as you showed the back panels that yours were missing. I always use these, modern receivers dont have them anymore. From what I can see manufacturers stopped installing them around 1993 (?). And I dont think your fix is spooky.
As with most things, the manufacturer's threshold is probably set lower than needed for liability purposes anyway... Thanks for your videos I really enjoy them! Please keep making them!!
The pre-out/main-in is for use with outboard equalizers. Now a days its probably used more for powered subwoofers. Nice unit. NAD makes quality gear. Thanks btw. I learn a lot from watching you.
Thanks! I certainly learned a lot from this project haha
It is a preamp and amp separation, so you can also pair it with another equipment.
Usually the methodology is collecting information about the fault, reading the schematics, probe the pcb then decide where to go deeper. This one is a wow process.
This is called "method of scientific butting"
Mokslinio badymo metodas :)
You should try to set the bias and bring your millivolts that are coming out on your speaker terminals down as low as possible the Safeguard your speakers it measure your DC offset if you have your service manual there it'll tell you exactly how to do it and you should be able to do it very easily it will instruct you on how to do it and using your multimeter and some of them you have to use a certain resistor in line with it sometimes you do sometimes you don't but you just do one side at a time if you have two meters you can do them both at the same time set your DC offset and your bias and you shouldn't have any problems and it should recommend it should be right there in the service manual what they recommend you set your bias and your DC offset at and you shouldn't have any problems with it as long as everything is set properly
soon as i saw the back panel lol,i waited patiently for you notice the links were missing ...
haha this fix was certainly a learning experience.
You can put external DC protection module outside of amplifier and bypass the internal DC protection, since you have UPC 1337 IC. Avoid stacking, those amps get toasty pretty quick
Just an fyi, but it's not adviseable to use computer thermal paste on transistors because most of those types of thermal oaste are electrically conductive due to containing silver. That can cause the transistors to short out. There are specific non conductive types of thermal compound specifically for use with transistors. Also the hfe value is the gain of the transistor, as in how much amplification multiplication it will give for a given input.
Theyre ditching silver these days, too many crying computer geeks. Most of the pc stuff is non conductive atm. Although they have started using diamond powder 🤦 (if they have it theyll find a way to sell it).
The white paste is mostly always not conductive.
Instead of MICA Insulators (when collector is hot, +V), I use NTE Thermal Pads - Better.
This was enjoyable to watch.. very engaging.
Funnily enough I picked up an amplifier that was dumped outside a house in a street nearby; but the left side of any output doesn't work (I haven't tried speakers yet though, just headphones). I have no experience so it won't be getting fixed; but it was interesting seeing you go through this process.
Regarding the higher value resistors to change the threshold, first of all, nice bit of investigation in determining what the issue is and how to change it. However, I would strongly suggest that you keep working on it, because there is definitely something out of spec that is causing the measured values to pass the original threshold. Given that must be the case, over time that will likely drift further and if you're lucky it will just start tripping the relay, if not it could damage your speakers, as you're already aware, but it could also damage other components. You probably know this too, but many components can test fine but still be bad, which can make it a roysl pain to find the culprit. Capacitors for example can measure as being fine in terms of capacitance, but have really high esr, which you won't see unless they're tested on an esr meter. It may be worth replacing the caps in the protection circuit even if they test good and then check if the original threshold is still being passed. Anyway, just my 2 pence worth of free advice. That's what I'd do, but you must do what you feel is right, of course. :-)
Thanks, I'll definitely be taking it apart again to look at it some more; I've gotten some great advice in these comments, so I don't feel too lost anymore haha.
@@HifiJelly that's excellent to hear. I hope you manage to get it back to spec. As you said in the video though, you're using it for learning purposes, so regardless of the final result, no doubt you'll enjoy the learning experience.
@@juddery I would recap it while it's tore apart anyway. Wouldn't take too long. What do you think about the idle current maybe being too high? I'm just spit balling here since I don't know what he's measured so far.
@@3dsmaxrocks699 in all honesty, I'm not sure what value the idle current should be on that model, or what the procedure is to adjust it. However, most that I've worked on have adjustment pots to set this. Normally a low amount of millivolts is perfectly fine although what is considered low on one model, may be considered high on another. Ideally it should be set to as close to the value specified in the service manual as possible, using the recommended procedure. It could also be that ageing components are causing it to run just a little over spec due to a drift in their original values. Without knowing the unit though, it's hard to say for sure.
@@juddery that's why I wish I was there with schematic LOL. I'm a locksmith by trade for 25 years.....and a electronics hobbyist.... and still learning.
Wow you've got more patience than me 😊
Ive got a NAD 7020e and if it stops working ill be sending it to the bin before i do what you did.
Hilarious. My favorite part was when he says "This handle on the back was probably the filthiest part of it" (while he's cleaning the part that is labeled "THIS IS NOT A HANDLE") LOL. I really appreciate you showing all of your screwups along the way...and shaving your hands before filming. Upvoted and Subscribed 😄
"New Acoustic Design" ... They've been going a few years now! ... A bit like myself! 👍🤣
Thanks for the experiment! The in and output that you had to bridge is for plugging a graphic equalizer in between the circuit.
I have a 7100X receiver with some troublesome speaker relais, now i use it more on a regular basis this problem solved itself and does fine now but you have to give these receiver some decent speakers to feed ,NAD,s tend to fall "away" on low volumes at one channel and mine has this low output switch on it that i need to switch off every single time i switch the receiver on.
This function when "on" makes you to turn up the volume a bit more so it,s solves low volume listening problems.
Great tuner function, very precise, and great ,very musical sound, these NAD,s do get quite warm when in use, so i do not stack anything on top of it .
I realy liked the video, seeing that the wiring mess inside is a normal thing with NAD, mine is the same,keep up the good work!
At 19:30 I noticed an unsoldered pin on the left hand side of the board. IMHO it's always a good idea to check out all the soldering. Cheers!
That's the speaker selector. It's an old alps switch. Some of the pins are unused. I had mine out and disassembled it to clean the internal slide contacts.
@@ctrlzyx2 Ah good to know, thank you
My Cambridge Audio Amp went into the highest protection mode for no reason. It hadn't been thrashed, mishandled or misconnected in any way. I took it to a local hifi repair shop and they couldn't find what had caused the circuit to kick in, but they said the only way to resolve it was to bypass the circuit, which they could do, but wouldn't guarantee any other components or my speakers would be protected. I decided to scrap it. I've since got rid of all my Cambridge Audio kit, (two cd players stopped working as well!) I now run Onkyo and Marantz kit which is a damn site more reliable, all bought cheap second hand. I plan to upgrade with new in the not too distant future so until then it's all working great!
Love those old nad amps, nice video👍
Thanks! Glad you enjoyed!
Hey from Australia. In my opinion, printed circuit boards are no ones friend. Yeah they're great in low power units like separate Tape Decks and Tuners that don't pull a lot of current etc BUT in amplifiers, especially vacuum tube amplifiers like I own (Primaluna HP Integrated Amplifier running 6 12AU7s on the preamp side and 8 KT120s on the output side) ventilation is essential. Primaluna valve amps run point to point wiring and any PCBs are low power that run their adaptive auto bias which is not in the signal path. All of the valve sockets are attached to the chassis with pencil sized holes around each socket to keep the amp cool. As soon as I saw a Primaluna HP Integrated Amplifier, I had to have it. $7,000 later and nearly 8 years later, it still sings and no more multi meters to check the bias of each of the 8 tubes. NAD have a strange setting on the back labelled (soft clipping). I've forgotten the logic behind it. I'm 63 and have been around electronics all my life. I'm an analog studio/visual enigineer and I was a club DJ over a 30 year period. Cheers for now Andrew Collins, Melbourne Victoria Australia.
You're asking for blown speakers hooking them immediately knowing it has "blown output transistors". Best to always measure the DC offset (DC at the speaker terminals) when first hooking up a broken amplifier.
The coupling links are there so that you can either use the pre out into another power amp or vice versa, or for adding an equaliser.
The handle is a am antenna
The PRE OUT and MAIN IN allows you to insert an equalizer between the preamplifier and the power amplifier.
Always loved the look of NAD's from that era
I do too, it really stood out to me when I first saw it. It has a very utilitarian look to it.
Those are pre out/ amp in jacks. The idea is to use that for an equalizer or bi-amping by sending the pre out to an electronic crossover and send the highs back to amp and use a separate amp for the lows.
It seems very similar to a guitar amp effects loop, where it sends the signal after the amplifiers preamp section then returning signal goes to the power amp. I also imagine you can also run it through some effects like of course EQ but also reverb and stuff.
@@SleepingLionsProductions yes, same concept. But the idea here is to split the signal with a crossover where the highs go back to the amp section and the lows go to a separate amp powering the woofer. It gets rid of the big time slurring capacitors used in a passive crossover.
With DC at the output you are going to either kill your speakers or bias the drivers and experience distortion. Since the DC at the output of one channel is not a zero (within a threshold) I would check every transistor in this channel, followed by the caps that impact ths DC bias. This amp has a fancy 2-stage power supply to ensure soft clipping so it could be something in this department as well.
hi those two connectors in the back that are not connected can be used if you want to connect one amp to another and use the amp as a pre amp and vise versa.
Interesting, thanks for the info!
Thank you for this interesting video. I own exact the same amplifier and I'm still happy with...😊😊
I repaired a NAD 3030 in about 1985 (!) and made the rookie mistake of hooking up my good hifi speakers which of course exploded. Best to use power resistors if you can. I did get it mended though, original fault was an earth wire under a screw which was slightly loose leading to voltage transients which took out the power stages. Didn't help the owner used it on Phono which gives the highest amplification. Soldered a new earth wire after repairing the power stages to prevent it happening again.
Check the service manual for the DC offset ( centering DC ) procedure. You can probably dial the DC voltage at the speaker outs to under 50mv optimal..
👆This right here
Yep.
This is correct and is outlined in the service manual. This amp is rather unique among Nad's in that it has distortion trim pots on each channel. You cannot get the offset adjusted if these trimmers are out of spec. With age these trimmers go to 100 to 1000 times their rated value. It is a known problem with the 7250pe (which I own and have repaired). These are 200 ohm trimmers. Mine measured about 500,000 ohm when I replaced them.
I'm going to have a go at my NAD C740 which sat unused for a decade and now has a similar protection cutoff issue. Also a neophyte at repair in logic circuits, but know enough to know that the caps will all need a close inspection. I have cheap DVM, ESR and LCR meters and hope to spend the idle winter hours trying not to let out the magic smoke. Nothing to lose and I might learn something. Schematics in hand!
Good luck!
I also had a C720BEE with protection circuit issues. Had it professionally repaired and recapped, full bias adjustment etc. Was worth every penny. Runs two sets of speakers and a sub in my shed. I also have a NAD 3225PE in the living room that I bought new in 1992. Always loved the sound of NAD amps.
Wow our thrift stores just slap $39+ sticker on electronics and put them on the shelf, ZERO testing. So that’s interesting, where are you? Subscribed:)
The pre-out/main in allows you to use a different external amplifier and then use the system just as a tuner/preamp.
I got a good laugh out of this, as a nad owner. cheers!
I'm kind of thinking he was using a graphic equaliser and disconnected it without replacing the links
I had a 3240PE, it was amazing! A lot of power to run my Dali 909 speakers.
I have this exact amp. Check r618 and r668. These are the distortion adjustment trimmers. Should be 200 ohm max and they are usually adjusted about half way (~100 ohm). These original trimmers develop surface oxidation and will ohm out in the kilo or megaohm range, i.e. way off. Replace them with 100 ohm resistors or new 200 ohm trimmers set to the same approximate position as the old ones. One of these is kind of hidden under a switch extension arm. These are 200 ohm trimmers with 5 mm pin spacing. I bought a bag of 25 on Amazon for about $5. the other trimmers don't seem to develop this problem, just the 5 mm ones. Once you replace these you can precisely set DC centering and idle. It will be impossible to get these settings correct if these trimmers are bad, as I suspect they are, because yours look original.
Weirdly my amp doesn’t have those distortion trimmers, it has the trimmers for idle current and dc offset, but the two for the distortion are just not on the board. The service manual I downloaded has them in the pictures for the amp adjustments, and I don’t even see a blank space where they would go. So I don’t know if I have a later (or older) revision that doesn’t have them, so yeah pretty weird.
I have the same amp that developed the same problem as the one in the video only after I adjusted the dc offset. Now no matter what I do it trips the protection unless I bypass the channel which is causing the issue. I read your comment and while it sounds plausible I struggle to find the relation between distortion and dc at the speaker terminals. Would you mind explaining why the distortion adjustment potentiometers would cause this issue ? Also would that fix still be possible for my amp or do you think that mine might have a different problem?
@@trevor245 I don't know why they call it a distortion adjustment. But it definitely has an impact on offset. In the schematic r618 and r621 are complemented by r626 which has a value of 680. R621 has a value of 560. R618 is variable between 0 and 200, or at least should be in that range. That puts it at a total resistance equal to r626 or at least close to it. If the resistance of the distortion adjustment trimmer (r618 ) goes sky high then there is no longer an equal ( or close) compliment to r626. It is way off. There's your offset. You can see why some people just replace r618 with 100 ohm resistor. Then the different sides of the differential stage have resistances of 680 and 660 (560+100), which is close enough.
@@ctrlzyx2 you ended up being completely correct. It was measuring 8Mohm. After cleaning it went down to the proper measurement again and the amplifier booted and played normally. I did spend like 5 hours yesterday fucking around in the circuitry but atleast it's working now. I will order some replacement pots. Thank you so much for your comment telling me what to do.
I wish there was someone like you local to me. I was given a Cambridge Audio One. It has a cd and DAB radio and of course speakers, which I thought would be perfect for my bedroom.... but after turning it on no sound came out🤔 Seemed like everything was operating. Then I decided to plug in my headphones, sure enough they worked perfectly🤷♂️
Now I don’t have access to any repairers anywhere near me and I don’t have the skills.....( I could have replaced a fuse😬)
So it’s sitting out in my back room.... I did connect up the little bookshelf speakers and they had a good full sound for their size.
I need to find a hifi / electronics enthusiast on my travels.....🤔 hopefully she’s single too😬😂
Bob Cordell wrote a very good book about audio amps. Find PDF on the web, the rest you would have to learn by experience, building some diy kits (beware of some of the Chinese kits). Also some the parts are harder to find as the technology turned into class-D amplifiers and chips. The easiest good modern amp would be something based on LM3886 50W chip. Really very nice sounding device, way better than some of the old '80s amps or cheap class-D junk.
I have the exact same amp., which I bought new in 1987.. It still works like new. BTW, if you ever do fix that amp, buy lots of replacement transistors. When you sqeeze out thermal compound the same as you do toothpaste, those transistors will be blowing out like cheap light bulbs.
I have seen on other electronics channels that computer processor compound is not the same as audio transistor compound. Apparently they should not be swapped.
The pre out is to allow for a different power amp to be used and the main in is to use a different preamp. Yes, the jumpers are necessary to use it as a single unit.
Check your dc voltage at your speakers terminals should be below 50 MV.
That's what I'm thinking too. Maybe out of spec and overheating one of the transistors
Usually when power transistors fail, they will be totally shorted from C to E (the semiconductor turns into a “full conductor”) so checking that in circuit is usually enough, there will be nothing in an amp circuit shorting them together anyways - but you can also lift just the base to check the diode drop of the B-E junction just to be sure. Other types of failure like leakage, low Hfe, noise etc. are more of a concern with small signal or germanium transistors.
Can it be that you swapped one of the output transistors from L to R when you resoldered them? That would explain the DC offset because those transistors need to be carefully matched. Also there might be pots to dial the output stage in.
The thing with the 'EQ LOOP' happened to me, as well. But in my case there was a CD direct button which bypassed the preamp tone control for the CD input so I figured the fault must be at the tone control or input selector. Signal traced it out just to find out it worked perfectly - and to notice in the schematic that it wasn't connected internally. Yikes!
The IC you replaced senses if the power amp output is bad, eg. if there is DC output to the speakers which can be caused by the DC offset adjusted badly, or sometimes the components around that IC for the RMS detector have gone bad, then the IC will trip the relay. This is quite common on other amplifiers such as my Marantz PM7200/6000.
you should be able to adjust the DC offset in the amp (ie the trigger point) probably a couple of variceal resistors. If you can get a manual it should say how to adjust the offset, so you don't need the extra resistors
Great Videos, I hope he comes back!
Any idea what small bench amplifier he uses??
NAD=Nearly Always Defective
Did you check the speaker outputs for DC voltage ? That is the firtst thing i do before i connect it to any speaker . But great video's and great repair work , keep them comming !
13:15 it's for an Equalizer and/or Power Amp
I have always pulled the bridges and put a 15-30 band per ch Eq from pre out to main in.
Im at 15ish minutes some of those nad amps require you to have both left and right channels connected. XD
You know there is a sping on the pin where you put the reel on? You must pull it and spin it a little to fasten you reel😂👍
You could test the pre out with the additional amp you have over there and you could have tested the amp stage sending signal directly to the input.
13:15 They are for connecting a graphic equaliser to the unit.
Can shorted filter caps cause these transistors to fail like this?
As for those transistors. The β, that's the difference between the base-emitter current and the collector-emitter current, or amplification level to use a simple term. If the transistor has a β=200 and you're giving it a 1mA current B-E, the current C-E will be 200mA. If it's really far off., like it seemed with at least one of those you measured, you should probably replace the transistor.
You can adjust the 0 point and the idle current with R 618 and R624
And your speaker wire connections are totally in-correct.
I took my NAD 7400 receiver for repair and the guy is having a hard time finding the correct transistors/capacitors to complete the work. Can anyone suggest a good place to get those parts?
Good video.Wondering where you picked up the new multimeter?
Thanks, I had to order it through Aliexpress as I couldn’t find it anywhere else. It’s the Uni-t UT8803E
Did you remove the mica insulators from the output transistors and just mount them right to the heat sink? If so, they are going to short...
I removed then to clean the old thermal paste off them, but I put them back where they were originally located. I was curious what those were for, figured it was insulating them from the heatsink but wasn't sure why.
Do you have a digital microscope? I use them to check all the solder joints and for cracked traces.
I had a cursory inspection of the solder joints and nothing too obvious stood out to me. I do have a digital microscope, but with the stand it came with it wouldn't work very well on such a big device haha.
@@HifiJelly I've seen old radios that were DOA come back to life just by taking a heat gun and gently going over the PCB.
Main.
In issues with NAD are cold soldering.
Could be differential pair on that channel
this two bridges are for the external equalizer😂 measure the middle points between the amp for a DC Value. if a DC is there the secure switcher protect the speaker and switch off the relay.
hFE is the current gain, meaning that a hFE of 84 has a gain of 84. It's the simplest of the 'h' parameters, and likely the most important.
At 8:10 in the video, you need to CLEAN the board prior to soldering. All that old dead flux needs to come off. When you weld or solder, the bond area must be CLEAN. As in hospital CLEAN.
The preamp output and input are probably for an equalizer
!!! Some thermal paste has metal content in them which makes the paste conductive. Some transistors have a metal surface at the rear of them and base (?) connected to that. The ones here have a plastic rear so there isnt a problem here but if there is a micca pad and a metal rear surface ALWAYS use either thermal grease or ceramic based thermal paste and NEVER metallic ones (computer thermal pastes usually have metallic content)
set your bias to reduce the offset
Thanks!!!
wtf... how did i only see this video 10 days after it was posted
Transistor or resistor feeding the driver circuit
Pre out is if you want to use it as a pre amp for some other power amp...and main in is if you for some reason want to use it as a poweramp.
classic mistake to forget to check if the bridge is there.. done it many times.
I haven't passed the 45sec mark, and I know the "problem".
I used to own that exact model.
Pre/Main ?
Im not a technician but arent the metal bridges from pre-out to main-in supposed to go from hole to hole only without touching the metal around the port, while you used a cable instead and bridged the full port?!
That's Pre amp main amp, it's the relay driver
Giant transformer yup. Mine got me good right through the case when i got it home from the second hand store. I may have booted it all the way out of my house 🤣. It was pretty, shoulda really held my cool on that one. Teenagerness 🤦
That how it felt fixing a German Automobile
Wow this is hilarious please tell me you did homework sense😂
2:11 "THIS IS NOT A HANDLE" 🥺🙈💀
Jumper couplers.
You finally found it (and you can ignore 90% of the comments) but you had your answer on page 14 of the service manual. Good grief, if the idle currents and/or DC offsets are way out of wack then THAT'S WHERE YOU START. Even if the relay is tripping you can check DC offset at the input pin of the relay. Also you most certainly can check the output transistors in-circuit. Use the low ohms function (not diode check) and measure emitter-collector. Nothing in the circuit will cause a low ohms short circuit except a blown power transistor. The output stages consist of 2 parallel connected NPN and 2 parallel connected PNP transistors in a class AB configuration. If one shorted it's a good bet the other 3 got taken out as well. The biasing transistors could also have gotten damaged. Modifying the protect circuit was absolutely a stupid thing to do especially since you said you measured over 200mV and the optimum setting for DC offset is less than 50mV. You are proving the old adage that a little knowledge can be a dangerous thing. Oh and since this manual covers all model variations, it's a good bet the US version doesn't have the distortion adjustment pots.
I never saw the protection chip gone kaput, it's usually what you mentioned in your post.
@@pliedtka Yea, that's why I said a little knowledge can be dangerous. Imagine what damage you could do to your speakers if you send a high level DC to them....and whoooops!, my protection circuit didn't trip because I modified it because I didn't read the damn service manual.
You were very lucky to have been born with all knowledge, and never having made a “stupid” mistake.
@@ShadowsOnTheScreen You're kidding right? In this line of work, if you don't know what you're doing you get help from someone who does. You risk not only damaging equipment but possibly killing yourself in the process. Even in little amps like this you're still dealing with high voltages and currents. I've been in the aerospace business for 30 years. I drill into all the techs under me....if you don't understand something, get help. No excuse when you've got the documentation in front of you.
@@MrDmbright65 if you don't know how to interpret this information you can't really apply it. All he is risking here is damaging his speakers. You have to learn somehow. And you might be a person who is able to interpret documentation in a way that translates into actual real life application and that is admirable whether you worked for it or were able to do this from day one but most people are not capable of doing this. Atleast not without experience.
ALLOW ME TO 'REPAIR' YOUR NAD AT FIRST GLANCE: Before you even plugged it in or took the cover off .. I looked straight at your problem, which should have been obvious when you determined your pre amp worked but no signal to output amp. SEE BACK PANEL AND OBSERVE THAT YOUR TWO RCA JACK JUMPERS ARE MISSING FROM PRE OUT TO MAIN IN.
The jumpers are removed if using an equalizer in place of the jumpers. If you remove the EQ, the jumpers have to go back in otherwise there's no connection between preamp and amp section. If you can't locate replacement shorting shunts, simply use a stereo RCA plug patch cord to hook the pre out jacks L&R to the main amp in L&R.
'Fixed'
But now, what damage was caused doing unnecessary circuit work?
Don't worry .. many people, techs included, have overlooked this simple issue.
SOOO THE GOOD AND THE FRICKEN BAD. THE GOOD IS. IS THOSE JUMPERS HAVE TO BE IN. ITS SO YOU CAN HOOK UP 2 OR 3 OR 4 , 5 AMPS. THE BAD IS TONS OF PEOPLE SELL AMPS WITH THOSE MISSING AND THEY LIST THEM AS BAD AND WE GET EM CHEAP. THEY WILL WATCH THIS AND NO MORE CHEAP AMPS. THANKS ALOT. THINK BEFORE YOU SPEAK. YOU JUST ENDED OUR CHEAP AMPS. Oh they can click On then off if open because you take away shielding and feedback will make it overload and click off. And I seen the ending and its kicking off because of feedback from cover off or the transistors are leaky. I'd buy another one off eBay and compare. The if difference in trannys replace all they are in parallel. NEVER SELL THIS ULESS YOU TELL THEM ITS DEFINITELY BEEN HACKED UP. You Will learn Everything you touch will break later so try not to remove things you don't need to. You'll learn. I.did.
THE HANDLE. DUUUUDE THATS THE AM ANTENNA
Noooo !
He said 'acrossed' ...
There's no such word as acrossed or acrost...
Just like there's no such thing as calvery men, it's cavalry...
𝐩𝓻Ỗ𝓂Ø𝓈Ｍ 😏
Sorry but this is not a fix. I know, you put the fix word in quote, admitting that it's not fixed, but still, these kind of "repairs" are an eyesore for me. Soldering that IC in backwards was stupid but hey, we all making mistakes. But altering the DC detection circuit is not a good thing to do. You had the high DC on the output because one of the transistors (probably one of driving the pover transistors at the end) was partially bad. The high DC triggered the protection. Altering or disabling the protection circuit isn't a fix. And yes, 0.2V DC on the output won't kill the speakers but it is high, usually you should have only a few millivolts there. 200 mV DC will be already audible on some speakers, which has negative effect on the sound. The initial problem is still there, that transistor is still failing, and eventually it will fail entirely. Than you have to fiddle with it again.
I have been shouting to the rooftops where are the preamp amplifier Bridge couplers because you only remove them if you're going to hook up noise reduction or a equalizer and since you were not hooking up either one of those devices the bridge should be in there and that's why you were not getting any audio and that's not the only receiver that has that Marantz some Macintosh and several other receivers are set up that way and a lot of people have made that same mistake that you have and I'm surprised that the technician that looked at this did not realize it themselves but there are also some of those units have a switch on the back of the unit that will close that circuit so you don't have to have the Jumpers in there but NAD does not have that switch the I have worked on those many a Time I have bought many of them on eBay where they said that the finals were burnt out and comes to find that the bridges were not on the back of the unit they bought them at a garage sale they bought them out of storage units and they sold them for parts and many a time it's because the bridge is not with the unit simple mistakes but I guess you learned something after you did all that work you should pay attention to the back of the unit or you should read more about the unit before you start taking things apart
You mentioned handle that is not a handle that is your a.m. antenna do not use that as a handle it should State on the back of that thing do not use as a handle because if you do you will Snap It Off and then you won't receive any a.m. out of your receiver you know how many times I've had to replace those on customers and it states on there do not use his handle and my customers have used it as a handle and I pointed it out to them do you see what that says it says in plain English do not use as handle and guess what they did they used it as a handle and it stopped receiving AM radio because they snapped It Off and broke the connections Lessons Learned From mistakes are sometimes the hardest
I hope you put the correct value resistors back in. Check out xraytonyb he has a wealth of trouble shooting tips and videos. Great find on the NAD.