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trouble with a PSAudio p300
trouble with a PSAudio p300
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Old 21st July 2005, 10:13 AM   #1
Joseph0 is offline Joseph0  United States
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Default trouble with a PSAudio p300

I've done some modifications on a P300, which can be seen here:
Please allow me to ask for help.

The unit was working fine, but in listening to differences between op-amps on the MW2 card, I accidently put a module in upside down (there are sockets.. : ^ | ). The unit will power up without blowing fuse, but no output, and the display reads the red light in lower corner.

I'm not an electrical engineer, and this is my first DIY project, so I don't have much knowledge or understanding of circuits. I'm guessing a shorted op-amp, but when I use the diode/transistor test with a multi-meter I get: black at -Vin, red at Vout = .887V; black at +Vin, red at Vout = .886; this with both modules.

Click the image to open in full size.

The other transistors seem okay too, but I will check again.

Are there any suggestions?
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Old 21st July 2005, 12:27 PM   #2
jackinnj is offline jackinnj  United States
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trouble with a PSAudio p300
you might have blown the audiocom chip replacement set -- pin 4 of the AD825 and (whatever dual opamp you were replacing) is usually V- or ground, when you incorrectly inserted the chip this pin was connected to V+. I have had opamps work when the problem was corrected, and I have had them tossed in the dustbin.

PSAudio -- their engineers didn't quite do all the homework on the design of the fingers for insertion of the card -- this should be indexed so that it can be inserted in only one direction -- at least Tektronix, Fluke, HP(Agilent), and Boonton do it this way. Just a little inattention to detail.
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