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sx-950 power supply help

S

supergilson

Active Member
Well, I screwed up. I rebuilt my power supply with new caps and transistors. I even had it working.

I went to test the voltages and damn if I didn't short out pins 13 and 14. Stupid, stupid mistake.

It immediately blew fuses 2 and 3. Upon replacing them, the voltages on pins 13, 14, and 15 are practically dead.

I'm no electrical engineer, but I looked at the schematic and figured Q2 Q4 and Q6 are nearby, so I replaced them.

I currently have -0.3 volts at pin 15, -3.3 volts at pin 14, and -0.008 volts at pin 13. I do have my -62 volts at the collector at Q2. The rest of the board is outputting the correct voltages.

What else do you think I fried? I suppose I'll start testing resistors and caps in that area. Maybe zeners? Anybody know what zeners those get replaced with?

thanks in advance
 
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That did the trick, but now it's clicking in and out of protection. Do you think sending 50 volts to the protection board hurt something?

Keep in mind, it's coming off a major rebuild of the power amp.
 
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On the DBT
Make sure your PS voltages are correct.
On both amps.
Check and set the BC Balance and then set the idles to about half the spec.
 
yes protect circuit might have taken a hit ..q3 q4 jumps out to me .maybe not though if all all else good :idea:
 
The 13 volt zener was the problem. Until I could order a new one, I swapped in a 13 volt zener from a sx-1050 parts unit.

I am getting -46.8 volts at pun 15, but +49.7 at pin 7. Those run to the power amp boards, which are giving me some bad numbers on DC offset. (18 volts)


Would those voltages mess up the power amp, or should I look elsewhere?
 
Both sides acting the same.

I need to check to see if I made the same mistake on both sides. Outputs are new also. I used mj21195g and mj21196g.
 
What trimmers did you use?
Trimmer for the DC Balance?
Trimmer for the Idles?
There has been some confusion on the values.
The wrong resistance trimmer for the DC Balance will cause a rail like condition.
I can't remember exactly the deal. 500 ohm instead of a 5000 ohm? Or the other way.
Tsd71 knows.
The mismatch you see in the regulated is not causing the 18 volts balance issue.
But:
One other thing I've done is add in series a 1N4148 to the lower voltage rails zener. This evens the regulated. For some reason the 950 is off slightly. Not sure what the difference if any is. It's just more better.
Actually the plus side is part of the +13 volt supply. I think it has some influence and why the regulated is off by 4 or 5 volts. It's normal.
 
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VR1 and VR2 are both 10K trimmers, VR3 and VR4 are both 100ohm trimmers

652-3296W-1-103LF (10K)

652-3386H-1-101LF (100ohm)


I hope you are using a dim bulb tester before you blow something else up.
 
The trimmers are correct. I made that mistake once.

Considering the voltages wouldn't cause the problem, and it is on both boards, I just need to find what is likely my mistake. For that, I probably don't need to power it up.

Thanks for the help!
 
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