How fudged is my amp?

[barfhorse]

This might be deja vu for some of you here. I just read 9 pages of a thread from 2014 here of a user who had a Peavey Basic 112 combo amp where a couple of you helped diagnose and fix the issue.

So.. I come to you with a Peavey Basic 112 combo amp that my idiot 20 year old self fried years ago. I mismatched the impedance and the amp made a pop and no longer puts out any sound. When I turn it on it just puts out a loud buzzing sound and nothing comes out if I plug my bass in. I managed to open it and I believe I've located one of the parts that looks fried. I have decent soldering skills but not a lot of knowledge in audio circuitry.

I attached a few pictures of the inside. Is my amp fixable? Is this potentially the kind of thing where I could just remove the fried piece and replace?

Thanks y'all

 

[filmtex]

Possibly. But I wouldn't do it without a Variac and the knowledge of how to use it. And I've repaired my share of amps during my 50 years as an audio/video tech.
What likely has happened is the impedance mismatch, probably too little impedance because of parallel loads, caused high current through the final output and fried the resistor in the picture. It his very possible that the output transistor/s are shorted due to this high current situation and replacing the burned resistor is only part of the fix. You could also need final outputs, biasing components and even drivers. IMHO-Time to take this to a tech.
Here's a link on an amplifier forum about this repair FYI.

 

[agedhorse]

It’s time to put it back together (no tech likes to work on something that’s been monkeyed with) and take it to a QUALIFIED tech.

 

[fdeck]

I'd actually be surprised if the resistor was fried. That kind of resistor can get quite hot without self destructing, so the burning might just be the circuit board. On the other hand, the transistor next to it might be the casualty, and the power supply might be toast too.

In this condition, the amp could damage the speaker. A tech could make swift work of telling you if this thing is worth repairing. They could also conduct the diagnosis without doing more damage.

I'm a pretty good general electronics tech myself, and have been fooled by power amp failures, because everything is happening inside a feedback loop, so everything affects everything else.

 

[Al Kraft]

My vote is to take it to a qualified technician as well. IME the "perfectly obvious part that's fried/failed" is most frequently only a piece of the real story of what is actually in need of repair. Poor or inexperienced troubleshooting and/or "jump to the obvious conclusion" fixes can often turn an easily fixable problem into a repair that is no longer economically worthwhile.

 

[barfhorse]

I'd actually be surprised if the resistor was fried. That kind of resistor can get quite hot without self destructing, so the burning might just be the circuit board. On the other hand, the transistor next to it might be the casualty, and the power supply might be toast too.

In this condition, the amp could damage the speaker. A tech could make swift work of telling you if this thing is worth repairing. They could also conduct the diagnosis without doing more damage.

I'm a pretty good general electronics tech myself, and have been fooled by power amp failures, because everything is happening inside a feedback loop, so everything affects everything else.

It’s time to put it back together (no tech likes to work on something that’s been monkeyed with) and take it to a QUALIFIED tech.

Right on, I haven't done any work on it was just seeing if this would be a simple de-solder/re-solder with new part.

 

[fdeck]

Probably not, because of the likelihood of further damage including the power supply.

 

[Wasnex]

Often when a component fails, it takes out surrounding and/or associated components. Really helpful if you know a bit of elecronics theory and have some basic test equipment. Also nice to have a schematic which can probably be requested from Peavey.

It looks like the output devices are still available, so the amp is probably repairable. There may be other semiconductors in the amp that are no longer available, so not 100% certain. I have a couple of old GK amps from the 90s that have lots of obsolete parts that are difficult to source.

The question IMHO: Is it worth repairing? I went on Reverb and the same amp is listed for as low as $85 with local pickup. I would be surprised if you can get the amp repaired for less. Would it be better to put the money towards a new amp?

When you take something to an electronics repair shop they typically charge a flat rate, bench fee just to look at it. This bench fee is no-refundable, but if you go through with the repair it goes toward the total cost. The actual repair cost is based on the total time and parts. So if the repair is super easy/fast, you may not have to pay anymore than the bench fee. Of course that also depends somewhat on how high the bench fee is. If it's $40 then you will probably have to pay more. If it's $100, you might get lucky.

Good luck.

 

[barfhorse]

Often when a component fails, it takes out surrounding and/or associated components. Really helpful if you know a bit of elecronics theory and have some basic test equipment. Also nice to have a schematic which can probably be requested from Peavey.

It looks like the output devices are still available, so the amp is probably repairable. There may be other semiconductors in the amp that are no longer available, so not 100% certain. I have a couple of old GK amps from the 90s that have lots of obsolete parts that are difficult to source.

The question IMHO: Is it worth repairing? I went on Reverb and the same amp is listed for as low as $85 with local pickup. I would be surprised if you can get the amp repaired for less. Would it be better to put the money towards a new amp?

When you take something to an electronics repair shop they typically charge a flat rate, bench fee just to look at it. This bench fee is no-refundable, but if you go through with the repair it goes toward the total cost. The actual repair cost is based on the total time and parts. So if the repair is super easy/fast, you may not have to pay anymore than the bench fee. Of course that also depends somewhat on how high the bench fee is. If it's $40 then you will probably have to pay more. If it's $100, you might get lucky.

Good luck.

Thats a good point, I'd like to get it repaired at some point mostly for sentimental value. It was my first amp, bought by my dad when I was 13. I have other amps, Just hoping its not beyond repair. I have a good local shop I'll take it to soon for an estimate.

 

[agedhorse]

Right on, I haven't done any work on it was just seeing if this would be a simple de-solder/re-solder with new part.

Somebody has messed with it, the Kep-nuts on the output device are missing. What else has been messed with?

 

[agedhorse]

Thats a good point, I'd like to get it repaired at some point mostly for sentimental value. It was my first amp, bought by my dad when I was 13. I have other amps, Just hoping its not beyond repair. I have a good local shop I'll take it to soon for an estimate.

Any qualified tech should be able to repair this.

 

[arbiterusa]

Somebody has messed with it, the Kep-nuts on the output device are missing. What else has been messed with?

off on the first pic, on in the second.

 

[agedhorse]

Right device on the top picture and the second picture.

this raises a whole lot more questions, and why techs are wary of these kinds of jobs. Who knows what else is wrong.

 

[NOVAX]

I defer to aged horse.

 

[fdeck]

When you take something to an electronics repair shop they typically charge a flat rate, bench fee just to look at it. This bench fee is no-refundable, but if you go through with the repair it goes toward the total cost.

Where I grew up, the TV repairmen referred to this fee as the "bench press." It was the fee for lifting your TV onto the workbench.

I remember this because I worked at an Apple Computer repair center that was part of a governmental agency serving the public schools, and we did not charge a bench press. And the customer was allowed to watch. If it took 5 minutes, we charged for 5 minutes. Many repairs consisted of "the laying on of hands," which was just pressing all of the IC's back into their sockets with the palms of your hands.

 

[BassAndCigars]

I can't believe I'm the first one to mention this but, in guitar amps anyway one needs to be careful poking around inside an opened up amp. I'm NOT an expert nor do I work on amps myself but from what I've read some fairly high / possibly lethal voltages *can* be present even when unplugged due to charges stored in the caps etc. At least that's what I remember reading. Maybe somebody else who knows more can chime in here. I'm just saying............be careful if you don't know exactly what you're doing. See if you can read up on it somewhere. There are ways to safely drain the voltages but you need to know how. At least that is the case with tube guitar amps.

 

[mmon77]

Many repairs consisted of "the laying on of hands," which was just pressing all of the IC's back into their sockets with the palms of your hands.

I cannot even tell you how many times I've been asked to look at at random piece of electronic equipment I know nothing about for someone because they know I have an electronics tech background. I open it up, take it apart, look at it, scratch my head, unplug all the connectors, plug them back in, press on stuff, put it back together and, voila, it works.

At some point, I actually started doing that before even looking to see if I could find a schematic, board layout, or any kind of service manual.

Of course, this is just favors for friends. I could never work in a shop and charge someone for that kind of a "fix". Even if the problem was just an IC that walked partially out of a socket.

These days, those kinds of fixes are less likely with SMT components, which I think is a good thing, even though they are more difficult for the average person to (attempt to) repair. Sometimes, that also, is a good thing.

 

[Hand slap]

This might be deja vu for some of you here. I just read 9 pages of a thread from 2014 here of a user who had a Peavey Basic 112 combo amp where a couple of you helped diagnose and fix the issue.

So.. I come to you with a Peavey Basic 112 combo amp that my idiot 20 year old self fried years ago. I mismatched the impedance and the amp made a pop and no longer puts out any sound. When I turn it on it just puts out a loud buzzing sound and nothing comes out if I plug my bass in. I managed to open it and I believe I've located one of the parts that looks fried. I have decent soldering skills but not a lot of knowledge in audio circuitry.

I attached a few pictures of the inside. Is my amp fixable? Is this potentially the kind of thing where I could just remove the fried piece and replace?

Thanks y'allView attachment 4324801 View attachment 4324802 View attachment 4324803 View attachment 4324804

I was a PV service Cntr. Ironically that part might be ok,.33 ohm, but it’s been stressed, replace it. Pull and check 6 transistor, and all current limiting resistors associated with them. The 2 outputs, drivers, and pre-drivers, I have repaired Hundreds of PV amps, PM if you wish. The issue with PV, I would actually use PV parts, and not sub, especially the outputs. You probably have to order anyways, don’t cross, order from PV.

 

[dalkowski]

The question IMHO: Is it worth repairing?

First thing that came to mind when I read "Peavey Basic 112."

 

[barfhorse]

Somebody has messed with it, the Kep-nuts on the output device are missing. What else has been messed with?

That someone was myself tinkering, I put them right back on. Nothing else has been really messed with.