fixing broken audio equipment

[cowanrg]

hello everyone.

i was checking out ebay and there are a few items on there that look to be in great condition but are not working. given a good multimeter and a basic understanding of electronics (what's what, how it works, etc...) is it fairly easy to fix things? many of them that i am looking at power on, but dont work beyond that.

i guess, it this typically due to a component failure, that could be traced and then replaced?

[mrfeedback]

"given a good multimeter and a basic understanding of electronics ".
Who is going to give you that ?

Takes time, knowledge and experience, and only one way to get that.

"i guess, it this typically due to a component failure, that could be traced and then replaced?"

Doh !. You get to guess which one.

Eric the Electronics Fixit.

[MRehorst]

It depends entirely on the type of equipment. Power amplifiers are generally easy to work on, but anything more complex can be a problem, especially if it uses ICs. Many ICs are either unmarked or proprietary or contain custom firmware or all three and will be nearly impossible to replace.

Another problem is that component failures can and often do cascade- one takes out another takes out another, etc. You must replace them all, especially the first one or the problem will repeat itself the first time you power up after repair.

Then there's the problem of obtaining service data. You'll find service manuals for equipment often cost more than the new equipment, when you can find them.

Then there's the problem of lousy designs. Some brands are just crap, and even if you fix them, you'll have to fix them again in a few months because the designers cut too many corners (Carver amplifiers, for example).

If you want equipment to fix, just ask your friends, neighbors and relatives what kind of busted stuff they have laying around. I'll bet you'll get more than you can handle and it won't cost you anything.

MR

[cowanrg]

great thanks guys.

yeah, i figured as much, but there are a few on there that seem pretty simple. of course, they could turn out to be hell too...

i was just curious because i can get dvd players and stuff for around $1. its worth a shot. worst comes to worst, i gut parts, or resell it on ebay.

what's the percentage that if it doesnt power up the transformer is bad, and that's all that's wrong?

[sam9]

On simpler equipment you can take a mindless low-tech approach -- simply desolder everthing and replace it. Considering what a repair shop charges by the hour this is fairly cheap if inellegant. Of course, this assumes the transformer is OK, that there are replacements for all the parts and that there are no bias adjustments to be made.

I'd bet that 1/3 to 1/2 of the non-functioning e-bay "prizes" simply need switches, connectors and pots either cleaned or replaced.

[cowanrg]

ok, thanks a lot. i figured that 2 out of 3 times it would be something simple. especially if its just and amp (not a fancy mp3 receiver or something...) plus, if it turns on, light up, and "appears to work" but just no sound, its maybe something simple. well, cool, thanks.

Originally posted by sam9
On simpler equipment you can take a mindless low-tech approach -- simply desolder everthing and replace it. Considering what a repair shop charges by the hour this is fairly cheap if inellegant. Of course, this assumes the transformer is OK, that there are replacements for all the parts and that there are no bias adjustments to be made.

I'd bet that 1/3 to 1/2 of the non-functioning e-bay "prizes" simply need switches, connectors and pots either cleaned or replaced.

[FrankDIY]

Originally posted by MRehorst
It depends entirely on the type of equipment. Power amplifiers are generally easy to work on, but anything more complex can be a problem, especially if it uses ICs. Many ICs are either unmarked or proprietary or contain custom firmware or all three and will be nearly impossible to replace.

Another problem is that component failures can and often do cascade- one takes out another takes out another, etc. You must replace them all, especially the first one or the problem will repeat itself the first time you power up after repair.

Then there's the problem of obtaining service data. You'll find service manuals for equipment often cost more than the new equipment, when you can find them.

Then there's the problem of lousy designs. Some brands are just crap, and even if you fix them, you'll have to fix them again in a few months because the designers cut too many corners (Carver amplifiers, for example).

If you want equipment to fix, just ask your friends, neighbors and relatives what kind of busted stuff they have laying around. I'll bet you'll get more than you can handle and it won't cost you anything.

MR

loosy design, this is the key. I have fixed a few technic amplifier of some friends and this almost always the same problem: the thing is heating to much that the solder melt or become really bad. Digital equipment are a lot more hard to debug.

[sam9]

Having said that a lot of problems are simply bad switches and connectors, I have to also relate that on some sufficiently old and peculiar items finding a exact drop-in replacement for a proprietary switch can be a quest suitable for Indiana Jones!

[annex666]

Originally posted by cowanrg
i guess, it this typically due to a component failure, that could be traced and then replaced?

I don't claim to be a genius, but in my experience just replacing a component that has mysteriously gone wrong may not help at all - for example if an output transistor has blown and you just replace it the new one may also blow due to the same (possibly unknown) reason as the first.

Generally speaking replacing components only works if the failure is due to the life of the component being reached or misuse/accidental shorting, etc.

[MRehorst]

Originally posted by cowanrg
i was just curious because i can get dvd players and stuff for around $1. its worth a shot. worst comes to worst, i gut parts, or resell it on ebay.

what's the percentage that if it doesnt power up the transformer is bad, and that's all that's wrong?

DVD players are going to be the most difficult to repair- full of ICs that you will not be able to diagnose or replace, and service manuals that cost $100+ each. These are exactly the sort of things to avoid. Don't forget you'll have to pay shipping on ebay...

Transformers are among the most reliable components in existence and most equipment has fuses that will protect the transformer from even a catastrophic failure in the circuits. It is a rare unit indeed that requires only a new transformer. If you do find such a unit, you have to ask why the transformer died- think about it- it is wire wrapped around steel- what can go wrong? The only way to destroy a transformer is to suck way too much current out of it. And what happened in the circuit to suck way too much current out of the transformer?

Avoid anything with moving parts (especially tape transports) and ICs other than basic digital or op-amps. That leaves you with some preamps and most power amps as candidates for self repair.

MR