At about 1.30am, the fan slid out enough to access the mosfet pins.?? A little tweaking and in next power up I see way more sane voltages on the transistors.?? 23.5v is gone. 1.5v to the driver base etc.???
Going to run through past messages and check it over agaaaaain.??
Still wondering what diodes I could sub, as well as q11.?
One thought...
Do you have a reliable bench PSU?
If so, you could temporally use it for the -12.6V rail, and see if the
rest of the instrument power's up, with the internal regulator disabled
and disconnected from the rest of the instrument.
Pull F4 (the 12.6V rail fuse) and connect to the downstream side of that
from the external PSU -ve, and it's +ve to chassis ground.
You'd have to make sure that both PSU's are switched on (and off) at the
same time, and that the bench PSU? has a working current limit/foldback,
set for at most 4A.? (Disconnect the flood gun filaments too perhaps,
"just in case"!...)
The only other "dependency" on the -12.6V rail, on the PSU schematic I
can see, is a resistor to the base of Q12 in the Calibrator circuit.? I
don't think that's going to worry about anything...
If nothing smokes, you could also vary the voltage slightly +- of the
set-point to check that the "Sensor Amplifier" (Q11) in the 141T's PSU
circuit is behaving correctly.
If the external PSU is stuck at it's current limit, or folds back, then
the root cause of all the trouble is deeper in the instrument.
As above.? Just an idea..
Cheers.
Dave B.
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