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a couple of fundamental questions

morroben
June 28th, 2010, 12:40 AM
In the interest of troubleshooting my amp without driving you folks batty with my problems, a couple of basic questions would help me out.

1. If a cap doesn't have voltage on the ground side (leaking), can it still be bad? Example: If I'm checking voltages on my coupling caps and don't show voltage on the ground side, can I rule them out as a problem?
2. Can a resistor test fine and fail only under load? Example: If a 220K (or anything else) tests at 220K on my multimeter with everything off, can I trust that it's not my problem when the amp is on?

Do my questions make sense?

laird
June 28th, 2010, 12:17 PM
Yes, they can still be bad in either case. I've had both happen, but both were my own fault. One time it was from running a 100v-rated cap at 150v for a few hours, the other was pushing 1.5w through a 0.5w resistor. :) Usually it's a situation where the component is intact but the internal insulation has been compromised just enough to allow arcing at high voltages. Real pains to track down!

Ronsonic
June 28th, 2010, 01:02 PM
In the interest of troubleshooting my amp without driving you folks batty with my problems, a couple of basic questions would help me out.

1. If a cap doesn't have voltage on the ground side (leaking), can it still be bad? Example: If I'm checking voltages on my coupling caps and don't show voltage on the ground side, can I rule them out as a problem?

Generally, yes. Generally. There may still be some sort of fault, but leaky is the most common for those.

2. Can a resistor test fine and fail only under load? Example: If a 220K (or anything else) tests at 220K on my multimeter with everything off, can I trust that it's not my problem when the amp is on?

Usually if a resistor is going to try and trick you like that it will go noisy and do the bacon imitation. You can trust that it isn't going open or short on you when you're not looking.

Do my questions make sense?

Yes they do. You can have some confidence that there's no weird science involved. While it is true that when amp parts go bad they become devious and conniving, they aren't very smart and only rarely come up with strange failure modes.

So what are you chasing? Might be easier than dogging it component by component.

morroben
June 28th, 2010, 01:10 PM
So what are you chasing? Might be easier than dogging it component by component.

Thanks for the input guys! Here's a link to the troubleshooting thread if you're interested.
the source of my staring and swearing (http://www.tdpri.com/forum/shock-brothers-diy-amps/217384-5e3-buzz-hiss-surprise-surprise.html#post2596625)