Princeton Chorus overdrive shuts off??

[turk05]

Ok.  I have re-started my efforts to find the issues with this amp.  Symptoms are the amp will not switch to the overdrive channel at times after switching to the clean channel.  I started the testing all over again, carefully.  I'm getting +7.74 volts at U12 pin 16, -8.03 volts at pin 7 and 8, no changes for any of the three pins when the overdrive switch is pushed on or off.   Pins 9 and 10 switch from +7.77 volts to -7.59 volts when overdrive switch is pushed.  Pin 4 to pin 3 is reading 63.0 kohms, pin 4 to pin 5 is 61.5 kohms, neither changes when overdrive switch is pushed.  Pin 15 to pin 1 is 76.9 kohms, pin 15 to pin 2 is 78.5 kohms, neither changes when overdrive switch is pushed.  U12 is a new chip (4053) if you remember. 

I know the amp failed to switch to the overdrive channel again last night when I was playing it, but with the board out of the amp, and no speakers connected, I am not wise enough to figure out how to tell if the amp is actually misbehaving or not when I test.  I had the board plugged in and turned on for 20 plus minutes when I took the above numbers today, and I retested each several times to confirm they were accurate.  This is more than the time it typically takes for the amp to fail to switch.  Last night it started to malfunction in under 5 minutes.

I also tested TP16 at U11, (pin 7) and for one test I got -15.18 volts when overdrive is off, +15.56 volts when overdrive is switched on.  Upon a later re-test, the voltage stayed at -15.18 when the overdrive switch was repeatedly switched on and off.   After I got the unchanging TP16 test, I powered the amp off and back on, and retested TP16.   The voltage repeated the first test. that is, it changed when the overdrive switch was pushed on or off. 

TP17 at U11 (pin1)  read +15.50 volts when Chorus is off, -15.21 when chorus is on, and tested the same at either time of the different TP16 tests. 

Does any of this help at all?  Is U11 bad?

I would really like to hang onto to this amp.  Any ideas based on the above numbers?

Thank you all.

[Jazz P Bass]

You have measured the U11 outputs but not the inputs?

Please post the input/ output voltages to U11.

In working mode & non working.

[turk05]

Here are the U11 pin voltages excluding pins 1 and 7.  Hopefully this is what you need?

Clean on: 2: -16.46
              3: -.346
              4: -16.48
              5:  +.352
              6:  +1.656
              8:  +16.06

Overdrive on:  2:  -1.659
                    3:  -.344
                    4:  -16.63
                    5:  +.656
                    6:  +.085
                    8:  +16.35