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MA500X Help?


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#1 JonRat

JonRat
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Posted 21 August 2005 - 10:26 PM

I have a common failure on 5000 and 5002...On powerup, signal/IOC remains on and CH does not pass audio. None of the internal LED's remain lit. It appears to be psu related as the Power supply for the bad channel does not appear to have the same +v and -v as the good channel. The good channel reads +-44v, the bad +80/-0.
The voltage off the 4 large bridge rectifiers all measure the same, so it seems isolated to the small board with the diodes, mosfets, and caps attached.

Is this caused by a psu problem? Or is this a sign of a bad output module?
Swapping Output modules did not seem to effect it.
Can I measure the +-V with the output module removed without damage?

Thanks for any help.

#2 KWhitehead

KWhitehead

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Posted 23 August 2005 - 07:58 AM

With a rail voltage shift as you described as have +80/-0, is normally due to a low side of bridge failure. SInce you swapped output module from side to side and it stayed in that channel I would say the problem is main board related. The Control board handles the switching of the power supply in and out of VZ mode. The low side swings the reference point +/- of VCC. So having the rail shift tells me the low side is hung up. You may want to check the low side on the main board to make sure there no shorted pre-driver transistors. If you need schematics you can get the MA5000VZ schematics off of the web site under Discontinued products. You should be able to use those schematics for the MA5002VZ.

Thanks,

Kip Whitehead
Crown Technical Support