Amplifier problem, need some troubleshooting help.

J

J.T. Pickering

Freshman
Jun 12, 2014
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Toronto, ON
I have a Yorkville AP4020 amp that has an issue, and I don't have enough knowledge of amp internals to know what to look for. Here's the problem:

Channel A works great. Channel B is not so happy. Sending it a very low level results in distorted sound. Sending it a reasonable level results in it immediately going into protect and stopping all output.

I opened it up to check for any obvious/visible problems but I couldn't see anything; although the way the amp is built makes it hard to see most of the internals without taking apart more than I really wanted to at the time I was working on it.

I'm reasonably handy with soldering and replacing components, I just don't know where to start looking for the cause of this problem.

Any advice is appreciated, thanks for looking!
 
Re: Amplifier problem, need some troubleshooting help.

The symptom sounds like the problem could also be a shorted output. Confirm that the problem stays with the same output when you swap speakers.

Of course be careful because a faulty amp could also damage speakers (but probably won't).

Unless you are knowledgeable about electronics, and by asking this question you probably aren't, look for a service facility.

JR
 
Re: Amplifier problem, need some troubleshooting help.

I did indeed test each channel individually with the same speaker and cable (and for what it's worth, I tested all of my cables separately with a tester as well). I'll do some quick tests with a multimeter to see if the output is shorted or something is shorted to ground.
 
Re: Amplifier problem, need some troubleshooting help.

J.T. Pickering said:
I did indeed test each channel individually with the same speaker and cable (and for what it's worth, I tested all of my cables separately with a tester as well). I'll do some quick tests with a multimeter to see if the output is shorted or something is shorted to ground.
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John is suggesting one or more output stage transistors is shorted; you will need to test each output device individually to find the culprit. When you or your technician find them, I suggest you replace all the output transistors for that channel, not just the 1 or 2 that are defective.
 
Re: Amplifier problem, need some troubleshooting help.

J.T. Pickering said:
I have a Yorkville AP4020 amp that has an issue, and I don't have enough knowledge of amp internals to know what to look for. Here's the problem:

Channel A works great. Channel B is not so happy. Sending it a very low level results in distorted sound. Sending it a reasonable level results in it immediately going into protect and stopping all output.

I opened it up to check for any obvious/visible problems but I couldn't see anything; although the way the amp is built makes it hard to see most of the internals without taking apart more than I really wanted to at the time I was working on it.

I'm reasonably handy with soldering and replacing components, I just don't know where to start looking for the cause of this problem.

Any advice is appreciated, thanks for looking!
Click to expand...

I believe this is a common problem for this amp. friends of mine did the same thing, the shop that repaired said it happens to that amp. What the problem was I don't remember, It cost just over $100 for repair.

Edit:

I got hold of my buddy this is what he said,

"
Lots of bad components bad traces
$115.00"

If this helps or not, it needs a visit to a shop.
 
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Re: Amplifier problem, need some troubleshooting help.

Yes shorted output devices is a common problem (it's how they fail) but no I was not suggesting the poster repair it himself. Often you need to replace more than just the failed output devices so an incomplete DIY repair that didn't fix all the problems could get expensive and blow up the new replacement transistors too.

Unless you know what you are doing, get some professional help that does. Since you said you have a VOM, measure the DC voltage of the output. If it is pegged to one DC rail or the other that is another sign one or more output devices are shorted, and will also eat your woofer in a NY minute (less than 60 seconds).

JR
 
Re: Amplifier problem, need some troubleshooting help.

Since I was a bench tech for most of my career-I will add this.

Even when you find a defective component-DON'T STOP THERE!!!!!!!!!!!!!!!!!!

I would always check every "active" component in a device (transistors-diodes etc).

Very often something ELSE caused the failure.

Look VERY carefully at the resistors-some of them burn with just a tiny band of burn.

Be sure to check all the emitter resistors.

If there are any ICs that are in sockets-swap them between channels.

i will admit that I did not do this every time-but only on amps that I had fixed the same problem many times before.
 
Re: Amplifier problem, need some troubleshooting help.

Ivan and JR are correct. This isn't like changing a spark plug. I've bench repaired at a hi end audio store in Reading PA. Fixed my own Phase Linear's, Audio Research, CJ, SAE, and there are bias and driver stages that all need looked into. This isn't something a look under the hood will find. Sometimes it is even the protection circuit.

Friends don't let friends fix amps.
 
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Re: Amplifier problem, need some troubleshooting help.

Ok, thanks for the replies everyone - and, point taken. I agree that this repair is beyond my capabilities. I'm asking around locally for the best place to take it now.
 
Re: Amplifier problem, need some troubleshooting help.

I would suggest that it might be better to send it in to the manufacturer. If a local shop has a good reputation and is experienced with this unit you might do ok but if they aren’t it make take them a long time to find and fix the problem and if they are charging by the hour it could get expensive. Some manufacturers have set pricing to fix their stuff so I would suggest that you talk to them. They are usually better equipped to do the work properly on their own products. And if you don’t have a box they will usually ship you the proper box to ship it to them in.

I was dealing with a client that had a problem with a Roland drum machine someone plugged the output of an amp into the output of the unit. I told them to send it in to Roland, they sent it to an “authorized service center” they had it for months and they never could fix it. When it came back they sent it to Roland and it was fixed and returned in a rather short amount of time. They never reincorporated it in to the band and at some point gave away all of the pads, I now have the drum machine because it was of no use to them anymore.
 
Re: Amplifier problem, need some troubleshooting help.

J.T. Pickering said:
They're actually much closer than that - in Pickering, just outside Toronto. (No, no relation to my last name...)
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Nice, The fall's yorkville is 20 miles from me in the Us, so never looked up the Canada location, You don't have to deal with the bridges either!!!!! One day 5 min to get across, the next 1 hour,,,,,,. Let us know what parts were bad!
 
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