Think whether the elevated filament circuit could have had one of its nodes (either input or output) shorted to ground, or elsewhere.
That would put excessive DC voltage across the regulators, and pop them.
That would put excessive DC voltage across the regulators, and pop them.
This is important. We previously reasoned that if all three regs are bad, it most probably is that the common input voltage is missing.
But now they really are proven dead. You could think that they were all at the same time shorted out, but these chips normally all have internal current and dissipation safety limiting.
What about the possibility that they were overloaded at their input? That the nominal 22VDC was for some reason, some short somewhere, accidentally too high?
Jan
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@jan.didden I never touched power supply until I started having trouble. If something affected the input voltage, it would have to come from the preamp unit.
@rayma What do you mean by “elevated” filament circuit?
I was able to source three replacement voltage regulators from ARC, so I can change them out once I sort out the umbilical connector
@rayma What do you mean by “elevated” filament circuit?
I was able to source three replacement voltage regulators from ARC, so I can change them out once I sort out the umbilical connector
The entire (lower) filament circuit is floating (not connected to ground), and is raised above ground potential by a resistor voltage divider (R43/R44)
that is set at around +122VDC.
that is set at around +122VDC.
Oooh, yes, I noticed that. Wasn't sure what the deal with that was. It's possible I connected the two circuits, which would have done a number on the grounded one I imagine. What's the purpose of floating and elevating the second circuit?