ZPA0.5 techy question

[gfunk_nz]

I've just been replacing some driver boards on a friends 0.5 after the repair shop had been in there. The boards I've put in are rev D whereas the ones out where rev A, will that make a difference to anything,about all that was different immediately was the bias pots where wound further round. It did seem though that one channel had more output than the other, that was just by ear and without having it on a good meter with a set tone it's pointless guessing.

The thing that did concern me though once it was running was I could hear a very high pitched sound almost like a cap that's not happy. when I was keeping an eye on it I also noticed the vertical board that fans plug in to had signs of excessive heat, sure enough the 3 big resistors at the top where friggen hot. I was wondering if one of the tiny caps on that was making the noise and possible shorted causing the excess heat through the resistors. I can possibly salvage that same board out of the burnt up amp the rev D driver pcb's came out of if needed. Can I get some input on that little story.

[stipud]

High pitched sound from the amp itself? Thats usually the torroids.

Or do you mean out of the speakers?

[gfunk_nz]

no the amp itself, infact with the fans running I can't hear it, so it's quiet

[ttocs]

the fans in my octane make a high pitch squeel. Try putting your finger on them and slow them down a little and see if it changes pitch or stops.

[stipud]

the fans in my octane make a high pitch squeel. Try putting your finger on them and slow them down a little and see if it changes pitch or stops.

Or press against the torroids. If the humming stops all you need is some epoxy to keep it from vibrating.

[gfunk_nz]

ah I'll give that a go, I first noticed it without the fans even connected so not them.
Now I've just got the other issues of the board that the fans plug into getting mainly just the one big resistor at the top getting really hot and then whether or not the rev D boards are ok to use and if so how to check the bias is set right.

[gfunk_nz]

I made a mistake in saying the bias pots on the upright boards, just read the bit about DC offset, it's the DC offset pots, I just measured each channel, hopefully did it right, no input just amp powered up, left channel was pretty ugly at a bit over 100mv, right channel for a start I had to swap the leads round so negative meter lead to positive speaker terminal unless I was mistaken, but holy crap, 645mv!!!
Guess I might be needing to get that sorted before looking at the other heating issue, may well be the cause of the problem lol

[shawn k]

The resistors you are referring to can and will get hot. They are 2w (maybe 3watt I can't remember exactly) wire wound and can handle the heat just fine. I have a zpa 0.5 here where that same resistor has actually discolored the board from it getting so hot (because the resistor is literally touching the board), but the resistor still works and meters just fine. For the same resistor of the other zpa's I have, they are soldered to the board with a little more lead so they have breathing room, and won't discolor the board. I'm sure this is something PG picked up on and rectified with newer revisions.

So basically don't worry about the heat. They will get hot, but it won't cause a fire or anything of the such.