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Old 19th July 2011, 01:46 PM   #11
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Location: Louisiana
Post the DC voltage on the two op-amps near the RCA jacks.

IC#
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
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Old 21st July 2011, 05:37 AM   #12
m4ick is offline m4ick  United States
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pThe reading change depending on how long I have been testing. When cool it powers up and for a moment you see -15v and +15v, all the rest zeros. After a second or two they read this (all + voltages):

IC# U1
Pin 1: 13.5
Pin 2: 13.5
Pin 3: .4
Pin 4: .8
Pin 5: 15
Pin 6: 13.5
Pin 7: 13.5
Pin 8: 13.5

IC# U4
Pin 1: 13.5
Pin 2: 13.5
Pin 3: .4
Pin 4: .8
Pin 5: 15
Pin 6: 14.1
Pin 7: 13.7
Pin 8: 0

After it warms up it goes back to +15v, -15v, and all others zeros. If I turn it off and back on it stays that way until I let it cool down for a few minutes, then I can get the above readings. Also, it seems that the channel I did not repair now stays cool and the bank I did not replace (tip36c) in the channel I repaired is now getting hot the fastest.
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Old 21st July 2011, 06:27 AM   #13
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You need to determine why pin 4 has no -15v. Confirm that you have negative rail voltage feeding the input of the negative voltage regulator as long as the power supply is operating. Then confirm that you have output from the regulator as long as you have input to the regulator.
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Old 21st July 2011, 04:28 PM   #14
m4ick is offline m4ick  United States
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It does produce -15v at first and again after a few moments. Are you saying to investigate that during the 10 or so seconds it does not produce -15v?
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Old 21st July 2011, 04:53 PM   #15
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Yes
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Old 21st July 2011, 08:13 PM   #16
m4ick is offline m4ick  United States
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Ok, apparently it was my mistake. I had B+, Rem, and GND connected and flipped my power supply on so the primary caps were not charged when Rem was supplied.

If I power the PS on with Rem disconnected and then connect Rem both of the op amps read:
0,0,0,-15,15,0,0,0

One channel has 0v DC, the other has +.4 and rising. The amp attempts to come out of protect and the transformer buzzes and it goes back to protect. That is at the emitter resistors.
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Old 21st July 2011, 08:20 PM   #17
m4ick is offline m4ick  United States
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Ok, nevermind, I take that back. It must have been warmed up again.

I see about +40 and -40v at the regulators while the -15v reg produces .8v. After the "warm up" the rail voltages drop to ~35v+- and the -15v comes up.
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Old 21st July 2011, 08:53 PM   #18
m4ick is offline m4ick  United States
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Sorry for all the re-posts but these symptoms are the strangest I've had to deal with.

I just hooked both oscope probes to the regs. On a cold power up the rail voltage goes above + and - 40v and I see + and - 15v. Suddenly, after a second or two, the rail voltage drops below 40 and -15v goes to +.8v. After another 10 seconds or so I see both rail voltages drop slightly again and a fraction of a second later -15v is back. Both rail voltages drop slowly until some of the outputs are too hot to touch.
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Old 21st July 2011, 09:50 PM   #19
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Reduce the biasing (bias pots fully counter-clockwise) so the outputs don't draw any current and observe the voltages again.

Do the outputs stay cool and do the voltages act differently?

What are they using for the 15v regulators?
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Old 21st July 2011, 10:01 PM   #20
m4ick is offline m4ick  United States
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With the bias' down the outputs stay cool.

The rail voltages are a steady +35, -35. The -15v regulator has +.8v on the output pin and it never goes to -15v like it used to.

The regs are Motorola 7815CT/7915CT. The regs are now heating up but I believe that is normal.
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