voltage problems

[ct]

Hi all,

I have had success with both an a12 and n72, but have run into voltage problems on final test of the j99.

measuring pin 4 to pin 3 on the opamp socket I am getting +23.1v
bettween pin 4 to pin 5 = -24.0v. (At first it was 13.1 and 14 before adjusting the r28 etc)

This is the same for both.

Additionally, at U3 pin 4 I am reading +14.7v and at pin 8 +38.6v (??!!).

I have tried swithching U6 and U7 just in case these were backwards, also visually inspected each resistor for correct placement and diodes and the polarized caps. Everything looks fine.

So I'm about to have to start pulling parts. Any ideas of what to do first? I can read schematics ok but am a little at a loss for troubleshooting.

Thanks, ct

[tele_player]

First, when taking measurements, make sure you're using the correct ground reference. The numbers on your op amp sockets look OK to me, you just need to adjust the pots. Try setting them at +20, -20; there's a pot for the positive and negative supply.

On your U3 readings, you don't say what you're using as ground reference, but the difference between the two (38.6 - 14.7 = 23.9) is is appropriate if they're at +/-12. Where was your ground reference?

[ct]

Thanks tele - I had been confused- pin 1 of J7 is on the right end. So the ground reference is pin 4 from the right. R28 and R32 were easy to adjust after I stopped adjusting both with an equal number of turns.

Everything is sounding good now.