incorrect voltages

[jimi]

i just finished putting together my second A12 and when measuring the voltage at pins 3,4 and 4,5 of U1 they are incorrect. I did set the variable resistors to their maximum CCW position. The voltages I measure are +/- 28 volts. I also checked the resistance at pins 1,2 and 2,3 of J7 and 1,2 is different than that of my first A12 (which works correctly). The resistance at pins 1,2 of J7 is about 9 M ohms, whereas my working A12 measures about 10 M ohms. Pins 2,3 of J7 measure about 8.5 M ohms on both A12s. I double and triple checked every diode and capacitor, as well as reviewed all the resistors. everything matches my working A12. Any ideas what is wrong?

[tele_player]

Have you tried turning R25 and R29 to see if they affect the voltages? I wouldn't expect the resistances measured at J7 to be critical - that's really done just to check for blatant short circuits.

It's been a while since I adjusted the A12 - are you certain that full CCW should yield the lowest voltage? Are you certain that you have the regulators (U2, U3) in the correct locations, not reversed?

[jimi]

ah ha! sure enough, i mixed up the voltage regulators. i guess i was going too fast this time and didn't pay close enough attention. so far getting them off isn't too easy...

[tele_player]

It's safest to cut them off, remove the leads separately, and (obviously) install new parts. Regulators are among the parts which can be damaged by heat, then you'd need to remove them again.