Trace Elliot clip light problem

[Axtman]

I have Trace Elliot bass preamps in for repair. The problem is no matter how much signal you put on the input, it does not light up the red LED clip light. It does light up the green and yellow LED just fine.

Here is a service manual for GP12SMX: SMX PRE-AMP.pdf

I have two other Trace Elliot bass preamps/amps that have the same problem.

[nosaj]

Ok on the schematic i don't see green yellow red LED i do see low Ok High. The doc says tr21 and tr22 develop the DC voltage to turn those on.
Have you verified the RED is good before you go too far into it?
nosaj

[Axtman]

Here is the indicator circuit. Low = green. Ok = yellow. High = red. I have verified that the red LED is okay.

[nosaj]

Whats your voltage at c116 and r78? Is tr28 good?
nosaj

[Axtman]

The voltage between C118 and R78 is 30 volts. So half of that is +/-15 volts. I could not measure the voltage to ground.

TR28 was removed and tested. I checks out good.

[g1]

The voltage between C118 and R78 is 30 volts. So half of that is +/-15 volts. I could not measure the voltage to ground.

I guess you mean top of R78 to bottom of C118 as shown on schematic? Why can't you measure to ground?

[Axtman]

I am not sure but it will not measure to ground.

And of course the indicator lights appear to be working! Heck if I know what I did!

[nosaj]

Well since you have 2 others same issue. Did you pull the transistor out of circuit? if so maybe you had some cold solder joints?
nosaj

[nosaj]

Since its working now see if you can measure c18 to ground and r78 to ground. A broken ground is sure to cause some craziness. Is the pcb mounted or out of the chassis, if out of chassis you may need a jumper from one of the jacks to chassis.
nosaj

[Axtman]

It turns out to be bad solder joints. I resoldered and the amps work!