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CR-3020 Amp board problems

Have you double checked Tr717 for shorts between e and c? This kind of thing almost always turns out to be silly issues …
 
I don't have the -H and +H supply wires (leaving the power supply) connected. C734 polarity is ok. I pulled C734 yesterday and tested. Tested ok.
(I do wonder if it is a schematic error.)
Thanks!
 
kcvintage said:
I don't have the -H and +H supply wires (leaving the power supply) connected. C734 polarity is ok. I pulled C734 yesterday and tested. Tested ok.
(I do wonder if it is a schematic error.)
Thanks!
Click to expand...
If +H is 12.6V then -H should be -12.6V so it’s unlikely that schematic is wrong in this case. I’d remove Tr717, measure Tr718bce, do a continuity test between Tr717 solder pads to make sure there aren’t any shorts and re-insert Tr717.

I know it’s a pain but there isn’t a whole lot to look at here, it’s a simple voltage regulator.

If nothing worked, hook up -H to whatever it should drive and measure again, sometimes transistors oscillate when no load is present.
 
Correct measured voltages below. Checked board and no shorts between leads or traces on either TR717 or TR718. I also connected -H lead to the headphone board, and no change in the -H voltage at the power supply.

I believe the problem lies with TR718, as its too high emitter voltage is feeding to the base of TR717, and driving up TR717e to -24.9 and thus the identical -H voltage at the board output connection. The TR717 Ve equals Vb plus -0.6, and it (like TR718) is brand new installed earlier today before the measurements below.

I traced the entire -H circuit, all components test good and all voltages match the schematic until I get to TR718. I am using KSA1015YTA for TR718, in place of the OEM 2SA844D. The identical +H circuit uses 2SC1890 (TR716).

TR717:
Vb: -24.3V
Vc: -24.9V
Ve: -24.9V

TR718:
Vb: -15.0V
Vc: -25.0V
Ve: -24.3V

Thank you for your help!!
 
just found a working, OEM 2SA844D. Am going to swap it in for TR718. I am very judicial with replacing OEM transistors, but had removed TR718 because the leads have "black leg" disease...
 
SOLVED. Connecting the proper grounding wires (E) to this circuit makes a difference. Good lesson. On to the relay section of the power supply. I had the PS board grounded, just not all of the ground wires were connected.
 
kcvintage said:
SOLVED. Connecting the proper grounding wires (E) to this circuit makes a difference. Good lesson. On to the relay section of the power supply. I had the PS board grounded, just not all of the ground wires were connected.
Click to expand...
LOL … something silly as expected. Good work.
 
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