NAD 502 cd player spinning in reverse at high speed - diyAudio
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Old 6th June 2012, 02:10 PM   #1
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Default NAD 502 cd player spinning in reverse at high speed

Hi guys, is anyone here familiar with the NAD 502? I recently acquired one that was faulty, no backlight (easily fixed) but it wouldn't load discs.
A quick look inside revealed the disc would not spin. After a quick tap on the board the motor gave a quick spin then quit, so gave all the solder joints in the vicinity a quick re-do, and went to power the unit on again to find it completely dead

Turned out it had blown the two rail fuses, so I replaced the 500 mA with some more and they blew again. I put some larger ones in there (not good practise I know, but they were all I had ) and upon startup, the motor gave a quick spin before reversing and then spinning at full speed.
I got the service manual and saw the spindle motor is controlled by half of a high current dual OP amp, a toshiba ta7256p. The other half powered the tracking motor. The opamp runs at unity gain, with a control signal from the servo control IC. I cut the track to isolate the IC to see where the problem was coming from and it gave the same behaviour as before, and the opamp IC would get hot.

The opamp motor driver is connected direct to the ps rails, and the motor is wired across the output and ground, so would explain its ability to spin either way, and I have thus concluded that the opamp IC is toast.

Hopefully I can just order a new one (only $10 or so, so worth the punt for an otherwise free cd player) and put it in, or is there a possibility it could have been caused by something else? Has anyone encountered similar problems in a CD player? I can send a copy of the schematics or complete service manual to anyone, but its too large to post here and still be legible. Any help is appreciated!

Last edited by flyingtele; 6th June 2012 at 02:14 PM.
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Old 6th June 2012, 07:11 PM   #2
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Join Date: Nov 2004
Location: Germany
Dead motor drivers aren't that uncommon. Usually a result of poor heatsinking.
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