On Wed, Mar 23, 2022 at 09:02 AM, James55 wrote:
This morning, I tested the +65v adj screw and it was working. Once CR1732
replaced with a 1N4148 however, the adj screw no longer has any effect and the
voltage remains at +61.8v.
There are really only two possibilities: The diode is bad (did it check 0.7V forward bias and open circuit reverse direction?) or it is inserted backwards (does the cathode really go to base of Q1732)?. This component is out of the picture in normal operation.
With CR1751 and the +15v rail re-connected, the voltage on the 65v TP drops to
about +39 volts. I don't have time now, but shall carefully go through all the
This one is most likely because +15V is in short circuit protection. Q1754 turns on steals base current of Q1752 by pulling U1724B, yanking its supply at pin 8 below 22V.
However, VR1724 should still keep base of Q1732 above +56V so +39V is not expected even in this condition. Perhaps VR1724 is bad, or if you replaced it before is it really a 56V zener?
I recommend checking diode CR1732 for proper orientation, and checking that you didn't get a faulty batch first. Then if you report voltages at pins 8 and 1 of the opamp, voltage across VR1724, voltage across R1724, and base voltage of Q1732 there may be clues.
Ozan
