Well, I pulled the E2 op-amp and replaced it with a NOS one of the same
model. Put the supply together and now I am getting -17 volts on pins E2
to ground (E10).
I'm thinking of just replacing the power transistor Q12 with a 7912 -12v
regulator that I have here and bypassing the whole op amp/transistor
mess. That should give me a solid -12v on the E2 line and provide power
for the -5 volt divider circuit.
Thoughts?
C
On 4/22/2020 11:52 AM, Jon Elson via cctalk wrote:
On 04/21/2020 10:09 PM, Brent Hilpert via cctalk wrote:
On 2020-Apr-21, at 5:27 PM, Chris Zach via cctalk wrote:
Meantime reading the manual I found an interesting test: If you short
emitter to base on Q4 (easiest way is to jumper diode D10) the
voltage on the -12v supply goes to .4 volts. They're saying it's E2,
R15,R17,R14.
Is there a way I can test the op-amp in circuit? Maybe it's dead.
Well, if the circuit **IS** regulating, then the voltage on the two
inputs will be identical.
But, since it might not be regulating, then these voltages would not be
equal.
But, if you can see that the + input is more positive than the - input,
yet the output
is pegged negative, for instance, then you know either the op-amp is
bad, or another circuit is overloading
the output and forcing it that way.
Jon
