Amplifier Akai am-u33, powers on, but no sound

No just the 3042's.
You could replace just the one, but from experience the other one is probably ready to go noisy also.
No real need to replace all the electros.
Other types of caps will be fine.

Dan.

Well, there is just one! No STK3042 pair in here.:)
The electrolytic were just a 5euro cost in total (didn't replace the 2 10000uf caps, perhaps another day). It was easy, quick, fun and cheap to replace them all.
 
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Hi Dan,
It would appear that standard procedures are different between our countries. We have had a spate of under rated resistors opening up in surge events that were normal in the equipment. Now, in the primary (AC mains) circuits we never install anything different than what is in the manual, including those chemical fuses in the power transformer primaries.

You could have just asked you know ...

I am very, very familiar with the characteristics of all the components I use, even when there are no legal ramifications. When the factory or distributor advises me to replace one component for another when it does not involve primary circuits, I follow that advice.
The OP has established that the module is noisy, experienced techs have said that this is normal failure mode.
Yes, and I stated the reason why I delayed and also after further information recommended that dlamprou replace the voltage amp. The output STK pak generally distorts during signal, typically they do not crackle. The voltage amp does.

Testing these STK packs while referring to the internal schematic is done by every good technician I have ever met before they condemn a part. I guess the customer really gets nailed in Oz, isn't that what you are objecting to? Being certain before committing the customer's funds on a guess?

Your attitude is getting a bit out of line in this thread, member to member. Downright insulting actually.

-Chris
 
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Hi dlamprou,
You only need to replace the voltage amplifier from the information we have so far. There is zero reason to replace both channels.

Leave the capacitors alone for now. Get it running before anything else. Once the receiver is running normally we can address your concerns or desires. You can increase the performance of this set a little bit, but it will not give much return in performance if you go replacing everything in the way of capacitors.

-Chris
 
My error....I had it in memory that the 3042 are mono, my apologies to OP for any confusion caused.
When the factory or distributor advises me to replace one component for another when it does not involve primary circuits, I follow that advice.
Fair enough, but replacing fusibles with non fusibles is not good practice imo.
It could be a legal minefield if the finger was pointed at substitution of components.....unlikely but just saying.


I guess the customer really gets nailed in Oz, isn't that what you are objecting to? Being certain before committing the customer's funds on a guess?
Now that is being intentionally insulting.
Of course, any good tech proves the fault before spending the customers money.
When presented with an amp with noisey symptom using 3042 and resoldering as required has been done, then it's a no brainer to replace the 3042, and no need to meter probe the device.

As an aside, after moving across the country, I worked for a Sony repair center.
I opened a job, and upon looking inside the particular unit, I remarked to myself that previous repairs were very well done.
I looked on the back panel and there was a sticker from another repair shop that I had worked for 12 years earlier...with my initials !.
The original work had held up perfectly fine, and the new fault was due to belts...as is expected.

Dan.
 
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Hi Dan,
Yes, I agree. My tone was to get your attention, and it worked. :)

I trained all my techs to check STK packs with a diode function before condemning the part. Too many were getting lazy, then back to me when the new STK did not fix the problem. There are a few key things to check, shorts and opens. Easy to do.

I have the same nice surprises. Looking at a previous job that was done years ago, telling the customer that it was a nice neat job. Then being told I did it. This happens more now after I sold my shop and old customers hunt you down to get more work done. This wouldn't happen if the average technician did good work.

I was taught to make it look factory, like you were never there (that has backfired - thank goodness for date codes!). That way its easy to see when someone else has been there. Once the distributors and other good techs get used to that kind of work, they would back me up over customers with false claims. I used to tag and sign my work a long time ago. Eventually my work became my signature.

I'm really glad you are a good technician Dan. There needs to be more of us than there is now.

-Chris
 
I trained all my techs to check STK packs with a diode function before condemning the part. Too many were getting lazy, then back to me when the new STK did not fix the problem. There are a few key things to check, shorts and opens. Easy to do.
Yes, lazy techs need re-educating/kick in the butt.

I have the same nice surprises. Looking at a previous job that was done years ago, telling the customer that it was a nice neat job. Then being told I did it. This happens more now after I sold my shop and old customers hunt you down to get more work done. This wouldn't happen if the average technician did good work.
The same has happened for me.

I was taught to make it look factory, like you were never there (that has backfired - thank goodness for date codes!). That way its easy to see when someone else has been there. Once the distributors and other good techs get used to that kind of work, they would back me up over customers with false claims. I used to tag and sign my work a long time ago. Eventually my work became my signature.
Ditto for me also.
I always flux cleaned resoldering work, and dressed cables back to factory condition.
Funny thing is, wherever I worked for other shops I got through 50%-90% more work than the other techs, and with close to zero returns.
We did some 12 month stats once...my completed audio jobs were averaging 52 per week and add to that diagnose/quote/order parts jobs.
My returns were less than 0.5%, and most of those were faulty customer.

I'm really glad you are a good technician Dan. There needs to be more of us than there is now.
-Chris
Likewise, thank you.
Our level of skills have become essentially obsolete.

Dan.
 
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Hi Dan,
Agreed.

I just got a call from a customer today who hunted me down. It looks like I will have to start doing service again. It is a new customer who just wants his equipment serviced. Nothing special, he just wants good work done.

My wife will not be a happy camper I don't think. I retired some years ago.
 
Hi Dan,
Agreed.
I just got a call from a customer today who hunted me down. It looks like I will have to start doing service again. It is a new customer who just wants his equipment serviced. Nothing special, he just wants good work done.
Lol.....your reputation precedes you.
If you are like my now retired electronics designer/manufacturer father you have far too much time on your hands.
You need some deep mental activity to keep dementia at abeyance.
My wife will not be a happy camper I don't think. I retired some years ago.
If some of that income gets turned into restaurant dinners or new wardrobe items she might reconsider. ;)

Dan.
 
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Hi Dan,
Reputations are a two edged knife. You can't live up to a mental image. After all, I just follow the service manual. Nothing spectacular going on.

We will see about a return to doing service. I have too many things to do, free time? What's that? There are a million things I want to do for myself. Things to design and build. A curious mind will make you a very busy fella Dan, and that is a good thing. In electronics, you never stop learning. You probably already know that.

-Chris
 
Hi dlamprou,
Have a look at TR12, 2SC313, +15 V regulator. Make certain it is working. TR1 and TR2 are your +/- roughly 20 V regulators - check-em.

You also have a bunch of fuse resistors - measure them because they normally look fine when burnt. You do have a speaker protection relay with power delay turn on via IC3, a TA7317P. If the relay doesn't go click after turn on, you might have a DC offset (measure the output of the STK2145 at the inductors (L1)) that would keep the relay from closing. There has been enough disturbed in there to cause a problem almost anywhere in your travels.

-Chris
TR1 and TR1B are a pair. Are you referring to this these. Any help trouble shooting much appreciated. I am getting voltages on the first TR1 but zero on TR1b.
I have checked the resistors between the two TRs. My problem is one channel is deal. THe relay works fine but I will still jump it to see if it solves the problem.
 
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Hi chinoy,
Okay, you need to focus us on the circuit you are working on, and your specific issue. It wastes a lot of time for us to try and figure out where you are and what you are doing.
if i join the right and left channel either at the input of the relay or at the output of the relay. i.e. short left and right channel. I get sound from both speakers.
You are kidding me - right??? You shorted the channels together! I'm sorry, but that tells me you haven't a clue as to what you are doing. What you did could instantly destroy both output stages.

Look, with respect I have to say this. You do not have enough of an understanding to attempt to fix any audio equipment of any kind. You have some understanding but not nearly enough. So you can get your back up and be determined to mess with this yourself, or you can take a moment and think about what you did and realise that the odds of you repairing this are remote, and even if you followed someone's instructions you would not learn anything. You are basically going to destroy this equipment and anything else you touch until you get more training.

I do encourage you to continue learning. However if you only want to fix something for yourself or a friend cheap, stop now.

-Chris
 
Hi chinoy,
Okay, you need to focus us on the circuit you are working on, and your specific issue. It wastes a lot of time for us to try and figure out where you are and what you are doing.

You are kidding me - right??? You shorted the channels together! I'm sorry, but that tells me you haven't a clue as to what you are doing. What you did could instantly destroy both output stages.

Look, with respect I have to say this. You do not have enough of an understanding to attempt to fix any audio equipment of any kind. You have some understanding but not nearly enough. So you can get your back up and be determined to mess with this yourself, or you can take a moment and think about what you did and realise that the odds of you repairing this are remote, and even if you followed someone's instructions you would not learn anything. You are basically going to destroy this equipment and anything else you touch until you get more training.

I do encourage you to continue learning. However if you only want to fix something for yourself or a friend cheap, stop now.

-Chris
Its cool I am self taught will figure this out also. With what has been done to this amp it cant get worse. In fact it was thrown in a dustbin (I got it for free). because everybody else had given up on it. Transistors have been swapped. Parts have been swapped. Tracks have been burnt.
This is a hobby and learning exp. Its not rocket science. Its a simple circuit and I have started by replacing all the caps and mismatched transistors. Im not afraid of blowing anything. It cant get worse than it is.
So far I have traced it down to a defective stk3042 which I will pull then swap left and right channels to the stk 2250 if the stk2250 works then its worth replacing the 3042 if both the STKs are blown it probably going back into the bin. Ill probably save the transformer. For my next diy amp.
I have spent the last 20 years building automotive circuits agreed this is my first audio circuit. And i have never worked with differential inputs and outputs. But thats the fun of learning new things.
20 years ago i got into the automotive scene out of frustration. And Ive done ok for myself. This on the other end at the fag end of my life is just for fun and something new to do.
This started out as a joke on my automotive forum. That I want to try and build an amp for my workshop. And people said na get something good not working and fix it and they have donated amsp / speakers / and some other gear for me to try and salvage.
The situation is one chanell is dead. And one channel works no matter what you do to it. And it works well.
The history is the 10,000 Uf power caps blew taking out a track. New caps were put in and the burnt power track jumpered.
But they never got both channels to work. It went from one repair shop to the next and finally landed up with me.
ps: You should come hang on my forum. And see how we ball rag the new noobs. I call it the entry price to learn.
 
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Forgot to add I have a scope and a function generator. So Im injecting a low voltage 50 hz signal and trying to track it thru the circuit.
You did give a good tip to debug the stk chip using a diode tester.
I did inject the wave on pin 15 and pin 1. But not getting any output signal from the STK one one channel. I will try and pull the STK and test it using your diode testing option.
 
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Hi chinoy,
That reasoning is not acceptable. Sorry.

Learning only has value when you begin taking the right steps and follow them using logic. You are starting off in a destructive, dismissive manner and are justifying your actions in a way that shows me attempting to teach you is fruitless. You have to change your basic attitude. Otherwise there is nothing that can be said by anyone except to take you by the hand and guide you as if you are a robot. No thanks, that is a total waste of everyone's time.

I've worked for over 45 years in automotive, test and measurement, audio, control circuits and more than I can remember to list, designing many. What you did is reckless in any of these disciplines. Because of this I responded as I did. You may have already destroyed that amplifier in fact. However, you don't even see this.

Since you admit that you do understand you are unfamiliar with what you are working on, don't you think it would have been more appropriate to tell us what your issue was, then ask for guidance? That would have saved time and allowed us to help you. But charging ahead the way you did, and doing what would normally destroy two output stages really shows me that you don't appreciate anything about troubleshooting. Your follow-up comments to justify your actions and question mine really illustrates you aren't willing to accept guidance at all.

I help more people for longer than you've been interested in electronics. I've trained technicians right out of school for decades. When I encounter someone with the attitude you are displaying I give them a chance to flush that and reconsider, or I cut them free. Others may try to help you here, and that's fine. But I've been down this road many times. To be frank with you, if you aren't going to adjust your way of thinking you may as well take that equipment to the back yard and soak it in gasoline and light 'er up. That's cheaper with a similar outcome, plus probably more enjoyable.

So this is me grabbing your head and trying to have you see your approach is completely wrong. Yes, it's gruff and I'll apologise for that, but you need a wakeup call. This is it. If you can correct your outlook I have no problem helping you.
 
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Hi chinoy,
That reasoning is not acceptable. Sorry.

Learning only has value when you begin taking the right steps and follow them using logic. You are starting off in a destructive, dismissive manner and are justifying your actions in a way that shows me attempting to teach you is fruitless. You have to change your basic attitude. Otherwise there is nothing that can be said by anyone except to take you by the hand and guide you as if you are a robot. No thanks, that is a total waste of everyone's time.

I've worked for over 45 years in automotive, test and measurement, audio, control circuits and more than I can remember to list, designing many. What you did is reckless in any of these disciplines. Because of this I responded as I did. You may have already destroyed that amplifier in fact. However, you don't even see this.

Since you admit that you do understand you are unfamiliar with what you are working on, don't you think it would have been more appropriate to tell us what your issue was, then ask for guidance? That would have saved time and allowed us to help you. But charging ahead the way you did, and doing what would normally destroy two output stages really shows me that you don't appreciate anything about troubleshooting. Your follow-up comments to justify your actions and question mine really illustrates you aren't willing to accept guidance at all.

I help more people for longer than you've been interested in electronics. I've trained technicians right out of school for decades. When I encounter someone with the attitude you are displaying I give them a chance to flush that and reconsider, or I cut them free. Others may try to help you here, and that's fine. But I've been down this road many times. To be frank with you, if you aren't going to adjust your way of thinking you may as well take that equipment to the back yard and soak it in gasoline and light 'er up. That's cheaper with a similar outcome, plus probably more enjoyable.

So this is me grabbing your head and trying to have you see your approach is completely wrong. Yes, it's gruff and I'll apologise for that, but you need a wakeup call. This is it. If you can correct your outlook I have no problem helping you.
Its all good. Having run many online communities for decades. I know how much effort and energy it takes So I appreciate the energy you put into this place. And this is your turf. So you get to set the rules. I understand how that works.
I signed up reading the DIY part. My mistake. Most DIY communities are used to dealing with newcomes.
This is a great resource. And i have found a lot of good info here. So thanks.

Its not worth getting too worked up over. Its a simple circuit and having access to the circuit diagram was the only reason I think this can be solved easily.
I dont think anything was damaged. And even if it was I plan to change most parts anyway. 90% of the replaced parts are not even with the right components. There is not one transistor on this board that is original other than the two STKs. And even that I doubt. because both have been re-soldered multiple times. And their pads butchered.
It would seem in my country the objective is to get it working with whatever parts you have lying around. vs ordering or trying to find the right part.
This is how I felt when I opened up my first engine some 40 years back. Same story. Mismatched parts. And utter and total lack of any will to fix it the right way.
When I got it one channel was dead. Only one channel worked. Its still the same. But I get your point. Even if I don't agree with you.
I will document the butchery and the wrong parts used if nothing but to educate people on what to watch out for. And will share it.

I will fix this and if your ok with it will share the story. When I get it working. So what it looks like is that if I can find a replacement STK it will get fixed. If not its going in the bin. Many guys are selling STK boards i.e. the complete STK setup on a PCB may look into that.
Yes I made a mistake I should have started a new thread. Sorry about that.
As to my attitude at this age I dont think its going to change. :)
No point in two grumpy guys going at it. Had this been my forum I normally send the guy a pvt message. But its not so cheers. Over and out.
 
Just came to update. Yesterday I got my amp working.
Had to replace both STK ICs. And a few transistors.
It took me a few weeks to source the original STKs. From the US. And a friend who works on audio dropped in to help me.
Replaced all the caps, both the STKs. and pretty much most of the transistors.
Very happy with the results.
For now I have it hooked up to some bose book shelf speakers.
And the next plan is to build some nice speakers for it.
The hardest part of the fix was figuring out what others had done to it. For example we found one channel audio was being feed to the speaker LEDs that is the original reason why one channel was not working. We had to strip the complete bezel off to access this small PCB and study what the last guy had done. The hint was the signal on one channel was a flat d/c out wave on the scope.
The best and easy way to fix this is to use a cheap function generator output a sine wave 1Khz. Into one of the input ports. And then trace that signal thru the circuit. Its really not that deep or complex.
Fixing this amp also gave me a legit reason to upgrade my 20 year old hand held fluke scope to a brand new Hantek Bench Scope. Man I love these new china made affordable DSOs. 100 Mhz free upgrade to 200 Mhz with some help from eevblog.