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Old 9th December 2013, 10:54 AM   #1
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Join Date: Jun 2012
Default CD Player; Negative dc at ac rails;


I'm struggling with my old Akai CD-62. After simple cap&opamp replacement at the signal paths, transport stopped responding. Sometimes it reads cd's for few minutes, sound is heavily distorted. After a while it does not respond at all. I checked my replacement parts orientation & compatibility. I also checked solder pads and traces. Couldn't find anything. I removed power supply feed from the main board and checked psu readings. Pin readings are correct, except Pin 7&8. There should be 4v AC voltage, but readings shows 2.4V ac & -15V DC! In the meantime STA341M gets really hot in few minutes. At the schematic STA341M feeds by +/-12V DC, I checked STA341M Pin 1&Pin 5;both reads ~6,5V. Final note; If I connect power supply to main pcb, all dc voltages at the pins goes down.

At first; how is it possible to have -15V dc at S5&S4?
Am I missing something?

I attached PS schematic.

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File Type: jpg PSupply.jpg (216.4 KB, 33 views)
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Old 9th December 2013, 11:39 AM   #2
DF96 is offline DF96  England
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Join Date: May 2007
The circuit diagram appears to say that the centre-tap on the AC winding is attached to a -20V rail via a 6.2V zener. I assume this is a heater supply for the display. I would expect to see something like -14V DC here, so -15V is probably fine.

You need to carefully check your "simple cap&opamp replacement at the signal paths". This sort of change, regarded as an upgrade, is often unnecessary and often leads to problems unless it is done one or two items at a time with careful checks in between.
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Old 9th December 2013, 11:53 AM   #3
Mooly is offline Mooly  United Kingdom
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As DF96 says, the PSU readings appear fine. You have to accept your problem is a man made issue and so you need to go over all the work you have done previously. Are the opamps correct (not fitted a single for a dual or vice versa). The STA getting hot may or may not be normal, I wouldn't just rely on that as a symptom though.
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Old 9th December 2013, 12:34 PM   #4
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DF96 & Mooly, thanks for the replies. In stock form it has M5532 opamps. I replaced them with OPA2134 and surrounding ecaps. Both opamps are dual channel. Anyway, I'll dig deeper tonight. Let's hope I didn't destroyed something!
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