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MA5000VZ Repair Checks

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We've just had to repair the CH1 output module on an elderly MA5000VZ. We've powered up, checked hi/lo bias and ODEP, output offset, (thanks Mr Glass for the diagrams) and run music through it, sounds fine etc.

But, just re-checking the Hi-Bias when it's cold, (no signal), on the repaired side, the bias reading changes as we move the front-panel gain pot! At minimum gain the hi-bias reads 358mV and at maximum gain the hi-bias reads 300mV! The low side bias does not change, and, of course, on the 'good' Ch2 there is no movement at all.

I've studied the diagram, can't see any reason why this should be!!

I've swapped the output modules, the fault follows the module, so obviously a slight fault still on the repaired one.

Any ideas, anyone..?? Cheers

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Its ok, sorted now.

It was R521 risen in value. Thank goodness, these can either be an easy repair or an absolute devil!

Amp back to its glorious self now! Worthy of its crown. :rolleyes:

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