SWR Workingman's Twelve

[xtian]

I replaced shorted output transistors and supporting resistors (marked in yellow), but there's still an issue. The +HV side is drawing current, as you can see by my voltage survey, and R23 gets very hot (dropping 48v). All of the transistors pass the test for shorts. Components marked in green measure OK. What can I test next to find the malfunction?

[g1]

The +HV side is drawing current, as you can see by my voltage survey

Not sure what you mean by this.
Is the 0.25V at Q3/Q4 collector a typo? Q4 is shorted?

[xtian]

Not sure what you mean by this.
Is the 0.25V at Q3/Q4 collector a typo? Q4 is shorted?

Not a typo. The -ve rail looks OK at -56v. But the +ve rail is only 0.25v, meaning something is shorting that voltage to ground. I'm trying to figure a strategty for finding the fault.

[Helmholtz]

Why doesn't this blow the fuse?
Q3 might be shorted.
Please post the schematic of the power supply.

[x-pro]

If Q3 is good, see Q5, Q8 and the whole circuit along this line to -HV. R38, R39, R39A

[x-pro]

Why doesn't this blow the fuse?
Q3 might be shorted.
Please post the schematic of the power supply.

Power supply circuit at the top of the schematic
F1 or in the field of power supply?

[Helmholtz]

Power supply circuit at the top of the schematic
F1 or in the field of power supply?

Where is F1?
Missing the schematic part with the mains input and PT.

[x-pro]

Where is F1?
Missing the schematic part with the mains input and PT.

F1 on the output.
With this bridge design, the low pass diodes and filter at 6800*63 are 2pcs. there is probably a simple 60Hz transformer in there.
Especially since the bridge diodes are not shunted by RC circuits.

[xtian]

Power supply is shown at upper left of first schematic. Here's another:

[Helmholtz]

F1 on the output.
With this bridge design, the low pass diodes and filter at 6800*63 are 2pcs. there is probably a simple 60Hz transformer in there.
Especially since the bridge diodes are not shunted by RC circuits.

Oh I see.
But I was looking for fuses either in the power supply or at the mains input.

[xtian]

Why doesn't this blow the fuse?
Q3 might be shorted.

Q3 base to emitter shows 820R. Fault?

[Helmholtz]

Power supply is shown at upper left of first schematic. Here's another:

Now here's another "F1".
Did you have a load connected when measuring voltages?
Did you use a bulb limiter?

[xtian]

No load connected. I stopped using my bulb limiter after observing no runaway. Device is drawing 10-12 watts from wall.

[x-pro]

Q3 base to emitter shows 820R.

What mode on the tester did you measure in? May be 820mV ?

[xtian]

OK, please rest your brains, and thank you for the help. I know I'm doing something boneheaded, here, so give me time to work it out.