How To Diagnose Faults In Transistor Circuits - A Practical Example Samson TXM16 1000W Powered Mixer
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- Опубликовано: 23 ноя 2022
- LER #328 So this started off as a repair video - and ended up as a kinda MASTERCLASS in Transistor Fault Finding and Diagnosis! Yeah it's 2 hours - BUT if you watch this through, maybe in a few sessions, you will learn a LOT about Transistor Circuits and HOW TO FIX THEM. Skip parts and you are gonna miss important stuff! Enjoy.
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Thank you
Richard
If there were more people like you, we would not have so much e-waste in the world. Your explanations are always great, keep on going. Thank you
And thank you for watching, without viewers this channel would not exist
DONT SHORTEN THE VIDEOS ! I am just starting out with electronics repair and although a lot of your procedures are familliar, I still enjoy the explanations of circuit design and why certain components are "in circuit" to limit noise, feedback, to block d.c. and other situations. Your continuous speaking/thinking out loud while you work gets my brain engaged so I can block out distractions and follow you along. This helps me with my own work. Thanks for the videos and your plain sight honesty in your work.
Hear hear! No such thing as too much information when it is all quality info. I need the details of how and why also..
Don't change a thing it's great that you are willing to go into the nitti gritty and explain your process and explain how the curcit works thanks for being part of the process Big thanks.
I am a repair tech and I watch these both to learn and to relax. So nice to see someone else saying "that just doesn't make SENSE...". Thanks for all your work.
I love seeing you make mistakes because you are not really sure about what reading on the meter mean, because then your figure it out and things start to make sense. This such a remarkably valuable and stimulating video to watch from beginning to end. I have learned more in the last two hours in one video than I have in the last several months of watching other videos. This is just what I was looking for. Practical steps I can follow. Thank you so much.
What a great tutorial, Richard! Learnt more in 2 hrs than all the other tut vids on utube. Gives me motivation to go back to my amp repair I've been at for 6 mths.
In case you have a class AB amplifier all the output transistors need to be biased to a point in the linear working ares of the transistors. This class G amplifier is a kind of class AB amplifier. That's what the potentiometers are for. The transistor that you incorrectly replaced (Q220) is the transistor responsible for giving a bias voltage to the bases of out output transistors. The NPN and PNP output transistors must have an output current running through them even if the input voltage of the amplifier is zero volt, else they are not working in the linear area of the transistors.
In case the potentiometer breaks, the voltage on the BE of the bias regulating transistor will go up, causing CE voltage to go down, causing too little bias voltage and thus causing non-linear amplification, because the output transistor are not in their linear working area (like a class B amplifier, but this is class AB).
You can measure the idle current over the emitter resistor of the output stage. Normally the service manual says what is the best value.
If you can't find the service manual I would set the idle current to 10mA. Your emitter resistor is 0.47 ohm, so that's about 4.7mV.
The perfect way to set the idle current is to use a spectrum analyser, put a sine wave at the input and set the idle current just high enough to make the cross-over distortion disappear.
did he fix anything, i fell asleep
It was a long video....but a long and utterly brilliant video that needs no editing! I've recently discovered this channel and am absolutely loving it. Your commentary, explanations, delivery and overall listenable appeal are the difference and genius of your output. Don't change, this is pure gold 👍
You are giving out probably the best information I've seen on electronics. Cool stuff!
Watched it straight thru. So very helpful. Been working on a NAD2200. I am an auto/boat wrench, an old dawg learning new tricks. Thank you so much.
Aside from obvious employment opps, I have finally embarked on my electronics-learning journey. Also due to my love of music equipment (especially vintage tho). I clicked on this without seeing whole title. Imagine the enhancement in my pelvic region… 😄💪 Thank you so much for the channel
Always learning a lot from you sir, hope you're getting well by Monday, looking forward to seeing this thing working as intended and you healthy again.
Great!
I've bee'n fiddling around with electronics for ages, as a former musician, but never realized to presolder, before unsoldering ... And it nice to have these videos smoldering around, and occasionally you pick up something you've always thought about, but never cared to understand. And the schematics
Get well SOON Rich! I always enjoy your videos so much and get so much out of it - if I wouldn´t have anything other to do (like sleep f.e.) I´d watch each on through in one sitting. I studied communications engineering at a sort of higher technical state school here in Austria - so basically electronics+programming. Start to work as a test engineer in a company that manufactures signaling devices for production plants soon. My first proper engineering job in the field (in my feeling).
I thank you for everything you do here. You´re awesome Rich!
Hey, awesome video. Don't change a thing. You're a great guy and a great teacher. When I found your channel about a year ago(?) I was very very pleased and happy.
Dont know how i stumbled on your channel but.... I LOVE IT.. something about you keeps me coming back "yeah" lol. Thank you from Ontario Canada !! Im a licensed auto tech who is learning how to repair modules and keys instead of always replacing!
I have just come across our channel and I have to say that it is truly enjoyable. I particularly liked the down-to-earth explanation of a G class ampm. Thank you. You now have a new subscriber and a Thumbs Up!
Great video. You are very knowledgeable in electronics field. I don't have a clue about any of this but great to watch and listen to.
Well hopefully after watching the video you will just be bewildered instead of being totally bewildered 🤣
These types of faults always are always a great learning and teaching moment!
These are such amazing videos. Thanks so much for taking the time - much appreciated!!!
Yes it was long, but I couldn’t stop watching it. Great video really enjoy the trouble shooting process and the circuit functions as they related. Hope your feeling better soon
Thanks so much for this! I did learn a lot. My main interest is RF as a radio ham but your teaching applies to a lot of that. So, I've subscribed.
Great video, worth every minute of watching. Thank you Richard!
I for one don't mind the longer video's, nor the mistakes . and I'm learning a lot so thank you.
ron
Really enjoyed and learned a tonne in this one.
Wonderful explanations as always and attention to detail.
Cheers again!
Great video, love in depth theory and diagrams, Im an electronics engineer, work mainly in tv at moment now, but love audio stuff especially vintage, i have a dynacord powermate 1000 mk2 powered mixer a bit higher end than samson i know, thants class ab with class h topolgy with the supply rails that switch from low level 52v to 104v when needed using a couple of mosfets on each channel, love the sound of the dynacord, seems unique, but great videos, always enjoy watching, keep em comming , looking forward to part 2 im sure you'll get it working, andy uk
Definitely ignore anyone who tells you how to edit your videos, suggest (nicely) that they get their own channel! Great video - guts, feathers and all - it's why we like them. Get well soon. Regards, David.
Thanks, I learned a small but significant function of the meter in DIODE test mode. I did not realize that touching the leads together would give a steady beep as a SHORT and on a good diode the beep would be brief and stop in the forward direction then no beep in reverse direction. This test mode will help me immensely in the future.
Heya your video's are not a waist of time I have already learned so much and still learning so I think I'm on the right path
Nice that you do a repair on audio. Something different than mobo and gives me a good idea what you do will have to face when dealing with audio. I saw this mixer in the car boot sail and was thinking: that would be interesting! And you ended up buying and repairing it! Cheers!!!
Thanks for sharing very informative and helps a lot specially those who starts in repairing .
Great tutorial, wonderful channel!
Good explanation at the start of the video on how the transistors are biased to just slightly be on and then the incoming audio signal turns then more positive or more negative...otherwise you could have saved time by starting by measuring each component individually...which u eventually did...
Sou do Brasil continue ensinando dessa forma pois assim eu posso aprender, estou começando agora e seus vídeos estão me ajudando.
Keep the videos the full length Richard!
Great video and as usual a very good explanation. (Also forget the exact numbers ... it's the concept that is important).
excellent video - thanks for sharing!
Love your method of training.
Better then a movie triller , can't wait second part.
hi Rich good time spent i hope you feel better soon best regards n4jrs 73
Legend!!! Thank you for these videos.
New video from Richard! Awesome!
I'd be interested in how you find the correct position of the trim potentiometers.
Thank you for your detailed videos! Don't shorten it! It's essential to follow your thoughts to understand what you're doing. If anyone thinks it's too long, no one is forced to watch!
best explanation of an audio amp, ever.
12.06 The minus almost nothing brought tears to my eyes , a classic 😂
@@mark-ec3ck I have a way with words 🤣
Thoroughly enjoyed it, even if I missed the live stream. Will make an effort to join the next live stream.
love your videos, learning a lot, much appreciated !
Great explanations. Thank you. Subscribed.
Great video - and class, in fact!
Thank you!
This is a very good explanation!
Wonderfully explained.
You are a legend Richard, teaching me so much 'Yeah...' haha :)
Wish you were on discord or something so I could pick your brains as I design circuits sometine
thank you for your dedication.
thanks for posting these
Really appreciated that - great explanation of Class G amps in the real world. Subscribing to see more :)
The base resistors are fusible types... ie they fail open circuit and dont burn......used in yamaha amps... great tutorial !!!!!
you're a very good tutor. i got my microscope btw and it's awesome. i can see stuff now.
and the first thing i noticed when using my new microscope is how horrible my soldering is.
@@frankbaron1608 Hahaha well there is a cloud to every silver lining LOL 🤣
awesome!!!!! thank you for these videos!
thanks for that. learnt loads.
Great video tutorial
Great work
Thank u sir...
I learn in ur chanel... 🇵🇭
Solder ratio of 37% Pb/ 63% Sn is the eutectic alloy and therefore optimal, in my humble opinion. It melts and freezes at a single temperature, which is ideal for 'iron' work since it tends to 'wet out' and flow easily leaving a smooth, shiny surface when it freezes. If you can get it easily, it is by far the best option. Incidentally, it also explains why the melting temperature of lead-free crap is lowered when this is added to existing joints.
That's my two-penneth, for what it's worth! 😁
I have a samson power amp thats failed. Powers on and the protection clicks off but can get a sound out of the bloody thing. Wasted about 4hr and cant find where the fault is. Great stuff btw, thanks for sharing all your knowlage mate.
thanks for the video Rich :) sorry to hear you're unwell bro during filming :) get well soon :)
Yeah been ill for about a week - seems like almost everyone here has had it - it's not enough to stop me, just enough to slow me down a bit 😆 but hopefully next week I'll be back on form
Another great video! I think the power dissipated when the transistor is fully on might be significantly more than 0W? Vce might be 1V for a BJT kind of power transistor? Even low power devices it might be 0.2V, so you'd still be dissipating 2.2W at 11A.
1:30:18 a big LOL that happenes more often than not, actually, HAHAHHAHA big salutes to you my friend, thanks for sharing this experience
Thanks!
Brilliant !
1:19:50 I think the name you are thinking of is called a long tailed pair. It forms the input of an Op Amp.
Awesome ! this should be 'required reading'.....cheers
16:00 - I like using the capital ‘R’ for ohms because it’s easier to write quickly. Also, it saves me the hassle of opening the Operating System’s character map, searching for the uppercase Ohm symbol and doing a copy/paste into the document or comment (e.g., 10R, 4R7, etc.).
Just keep going, like you are. No need to edit😀
1:53:41 Q214 cracked? Not sure if you've already identified as faulty.
The resistors are frequently metal film type and often flame proof in the audio output circuitry. I see in the comments you and the viewers have identified some resistors as fuse resistors. Possibly a good area for additional research and discussion.
Thanks for sharing your knowledge and experienced.
Get well soon .
Epic , schematic essential.
On the power supply there is a heat sink next to the 2 heat sinks for bridges
What is that for ? Obviously nothing to do with the problem though!
Trimmer pot vr201. If it's faulty and you replace it how do you know which resistance to set it to when you replace it. Is the value written on the schematic or is it to achieve a specific voltage somewhere in the circuit. Thanks Richard.
Briana for what’s it worth I also worked on valve gear way back in 60’s, I still do odd jobs on guitar/p.a.systems amps but the rest is solid state usually with FET output amps. The main difference are valve emission deterioration where transistors FETS etc do not suffer with age as far as I know! Transistor junctions can break down and cause a short and also go open circuit sometimes for no apparent reason? Poor thermal heat sinks can cause thermal runaway and clogged up fans in PC’s are a common cause. Another failure in solid state is spikes/static junctions short or go open circuit! Bias drift over a long period can cause clipping on valve circuits - I haven’t experienced this on solid state yet? Noisy transistors like resistors used to be a pain in the (a--) but a tin of freezer or hot solder iron soon weeded them out! Hope this is of some help! Fraser
What about the capacitors you mentioned in the beginning of the video? Cool Video, I finally learned how amplifiers work! And I understand now why I should have a signal generator...
Nu e musai, un generator profesional e suficient si un injector de semnal in jur de 1Kz care da destula excitatie sin cazul de fata daca AAF e bun si cuplat la dif pe masura sa la putere maxima i-ti vor tiui urechile cel putin o saptamina ha, ha, ha ca sa va saturati de 1000 W = 1Kw ati inebunit la ceva trebuie asa putere
As always, excellent video and tutorial. Can you provide info on the Thermal camera you are using please ? Regards
Cuan Hogan Richard made a video recently reviewing the thermal camera. Check out the video for an in depth look. I am thinking about buying one myself. There is a link for the camera where the video is.
Dont change a thing great video
+1 for a callout to Stargate. I miss those shows!!
Thank you soo much!
A little question please....
Can you help me with a Search term for your meter probes ?
Best regards from Bavaria:)
PS:
Looking how you try is never a waste of Time !
it remembers me to soo many things i knew....i could Not remember it without you .
it you have some Religion....your god will bless you for saving people from forget.
....
english Bad...i know:)
Would brute forcing the repair by testing individual components on the board with a multimeter be a viable option if we don't have the schematics available?
51:16 - I know you said you’re not firing on all cylinders; but, can a solder be ‘lead-free’ if it contains 37% lead?
Dickie, is that leakage from C21(?) (prob. C210, but can't read last digit - brown gunk, could be glue??)? It's the elec. cap. between VR201 and the ribbon connector WA102.
at 53:40, the transistor at Q213 on the right middle looks blown away... and those 2 caps look bubbled on top.. u seen those tho
great basic trouble shooting and just shows not to leave any stone (wires) unturned. Would you say using a curve tracer would have been efficient in this repair?
Nu
If a faulty pnp we're to be the case, would it cause clipping in the negative side of the signal? Please excuse me if it sounds like a stupid question, but my experience with amps are almost exclusively tube type but there are some similarities in their operations. Such as your npn-pnp circuit acting as an inverter in a push pull valve circuit. Again, please pardon me if it sounds like a stupid question as I don't know much about solid state low voltage amps. Thanks in advance if anyone cares to respond.
I think the resistors are simply Fusible Resistor types hence the FR in the schematic. Also in view of the fact that they have gone open without obviously burning out. Not sure of wattage sadly.
Ahh OK thanks for the info
Indeed, they likely are 0.6 W Fusible Resistors.
@@pavelvashev1893 Thanks
Low value carbon resistors are like to go open cct if too much current drawn
Why not try cold testing with E.R.S. meter, may reveal low impedance path in fault area? I have seen u use this method in laptop VRM’s before? Fraser/Elsa
Struggling to work out how to can add 90vdc to 45vdc without a big bang, surely the 45vdc rail has to be switched off?
Hello sorry on my english...I repair my txm mixer and I need that schematic diagram,I dont know te values of some resistors...can you write comment here..thanks
A lot certainly went wrong in that amplifier. A cascade of events of course. Quite involved.
This will be a different comment...Thanks to the World Wide Web, RUclips, all the search engines, browsers, Chinese technology to help share and fascilitate your magnificiant knowledge among all over the world community freely. Oneday you gonna be a legend. I hope you missed to explain why the higher power loss dissipated 45v using power transistors replaced instead of 90v supplied power FETs at once.
sometimes you can short with a 10 ohms resistor between the base to the E sometimes it works the problems is found
I don’t know how you can probe around on live circuits with these bare probes! I used to have a rock steady hands and had no problems but I am 78 now so probes are all insulated right up to sharp points for my own safety and for short risks! The joys of getting old! ha ha. Fraser
Cool...
man i hope you charged a good amount for that fix. thats quite a bit of time and effort. I watched in its entirety and yeah there is nothing you could remove from it.
those "minus almost nothing" voltage rails always cause me trouble :)
1:15:37 - Time for oscilloscope?
1:30:05 - Eh... Importance of proper visual inspection with LED light and board cleaning before attempt to fix...
1:52:33 - Its not resistor, its "choke" component.
1:53:23 - Those can be cleaned with contact cleaner, but be careful to know how to adjust them.