C84 Having some fluctuating problems

[jgriep]

Hello,

So I am finally getting around to trouble shooting a C84 that I never got working. The problem I am having is it is when I have all the opamps in, and mic plugged It starts fluctuating. The signal goes in and out, at about 2 second intervals. I am also getting an odd voltage across L3 and L4 that fluctuates at the same interval. It goes from about .5mv to 4volts. When I listen to the out sounds great for a bout 2 seconds when the voltage at L3,L4 drops to .5 but totally disappears when it bumps up to 4v. Any Ideas?

- Josh

[tpryan]

What rev of the board do you have?

[jgriep]

REV 1.9

[tpryan]

Are you sure you have the correct resistors installed at R31 and R32? Does it happen at all gain settings?

[jgriep]

I have 2.2M at R31 and a 100K at R32 which according to the schematic is correct. It happens at all the gain settings. The lower I go on the gain the slower the cycle of going on and off happens. There are loud clicks when I change the gain.

Thanks for your help Tim!

[tpryan]

What voltage are the regulators set to? What voltage do you measure at the junction of R29 and R30? Are you absolutely sure you have the correct resistors installed at R22, R23, R25 and R28?

[jgriep]

The regulators are set at 18v, All the opamps are getting a nice solid 18v at both positive and negative.

Measured the voltage at the R29 R30 junction. This seems really odd. It swings from +32v to -12v at the same rate the signal is going in and out. I also measured R29 and R30 to common from the power supply and it swings from +15v to -7v.

All the resistors are correct at R22,R23,R25,R28. 1Ks at R22 R23 and 1K58s at R25 R28.