Help with Mackie Big Knob Repair

Just following John Cleese

So I got the transformer this morning and soldered it to the board as it is now (disconnected from the rest of the PSU and no fuses blow and voltages seem to read fine.

I will replace diodes and caps this afternoon and report back. I'm pretty sure everything will be fine.

Cheers!
Sono

Hi again,

I've replaced all the damaged components but didn't have 130R resistors, so I used 120R ones. I get +16.5/-16.5 volts at the PSU output instead of 15V.
Is that related to the resistor I subbed? Is it safe to connect the rest of the circuit and use it? I'd rather be safe than sorry...

This is the Main Circuit:

This is the schem of the PSU:


Thanks a lot for your time and help
Cheers
Sono

Hi!

The viltage difference is probably linked with the resistor swap.

But i don't think it would do much harm, we're talking 3v difference. Mackie are known for reliability, i think their design should take a 3v difference in the teeth.

I can't see which opamps are used (image blurry here, bad internet tonight) but the best way to be sure is to look at their schematic.

Cheers,

Thomas

Thanks for your reply Thomas

totoxraymond said:

But i don't think it would do much harm, we're talking 3v difference. Mackie are known for reliability, i think their design should take a 3v difference in the teeth.

Click to expand...

Actually the difference is 1.6vdc. The regulated output of the PSU is now 16.5 and the circuit is supposed to be fed +/-15.

totoxraymond said:

I can't see which opamps are used (image blurry here, bad internet tonight) but the best way to be sure is to look at their schematic.

Click to expand...

As far as I can see and read a schematic the opamps used are NJM4565G, LT1115CN8, NJM2068, NJM4560, and LM339. I checked their datasheet and they all seem to work up to 18v so I guess I can fire it up?

Cheers
Sono

That's barely a 10% difference, and they wouldn't design such devices to run on the ragged edge of their ratings, so I'd be confident to reconnect everything and get the thing back into active service

Excellent Khron! Just what I needed to hear

Thanks a lot for your help!!
Cheers
Sono

sonolink said:

Thanks for your reply Thomas Actually the difference is 1.6vdc. The regulated output of the PSU is now 16.5 and the circuit is supposed to be fed +/-15.

Click to expand...

Yeah but the opamps are powered between both rails, so 16.5+16.5=33v against 30v originaly.

Cheers,

Thomas

Oh I see what you mean now
Cheers
Sono

Ok guys, it WORKS!  8)
Thanks again to all for taking the time to help me out 

Cheers
Sono