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Question about the function of a capacitor in a circuit

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fedaalis84:
So I think I'm going to wait until I get the right-channel transistors in before worrying too much.

The leads on the emitter resistor on the left channel read at about -20V, whereas on the right they read -4V (because the transistors are out, and not pumping any voltage).

The busted emitter resistor from before was reading a few mega ohms between the left and center pins. Now it's a functional resistor there. So those -4 volts are getting over to Q762. Could be what's leading to the protect, and explain why a random cap, and desoldering the jumper did nothing. But that protect did not start until I put in the new emitter resistor...

fedaalis84:
Definitely the protector circuit causing the shutdown. JW463 runs to the protect pin on IC702 and should be reading 3.3V, but instead is giving -150mV. Slowly rises back to 3.3V once in protect due to a big cap in the area

fedaalis84:

--- Quote from: xavier60 on March 02, 2019, 04:29:34 pm ---An overload protect detection will cause a voltage across R326, about 0.6V.
A DC protect detection will cause a voltage across R323, about 0.6V.

--- End quote ---

So, xavier60, if you're talking about only a 0.6V drop across R323/R326, and I'm looking at -150mV on JW463/Pin 87 on IC702 (Protect pin), should I be suspecting a short in one of Q323/Q324/Q325?

fedaalis84:
So I'm still seeing something strange with the main power rails.

On R545, the resistor for the positive power rail, I'm reading about -20VDC. On R546, the negative power rail, I'm reading -62VDC.

R545 should be giving me positive 62VDC, correct?

Also, something weird... The positive leg of the bridge rectifier diode reads a steady 62VDC even after the AC is turned off by the relay in protect mode. It doesn't drop, it just sticks at 62VDC... Weird, no?

xavier60:

--- Quote from: fedaalis84 on March 03, 2019, 04:00:09 pm ---So I'm still seeing something strange with the main power rails.

On R545, the resistor for the positive power rail, I'm reading about -20VDC. On R546, the negative power rail, I'm reading -62VDC.

R545 should be giving me positive 62VDC, correct?

Also, something weird... The positive leg of the bridge rectifier diode reads a steady 62VDC even after the AC is turned off by the relay in protect mode. It doesn't drop, it just sticks at 62VDC... Weird, no?

--- End quote ---
R545 must be open. The positive rail capacitor is staying charged because no current is being drawn from the rail. R545 and R546 function as fuses.
Don't bridge out R545. replace it with the same value or something close and hope that there is no permanent overload present.

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