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Old 05-21-2019, 08:02 AM   #8
budwich
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Join Date: Jul 2015
City & State: Kanata Ontario
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Default Re: Crown Amp DC300A - One channel distirted, other good.

Quote:
Originally Posted by Agent24 View Post
Could be a transistor problem, leaky, shorted, missing power rail. Might be better to do symmetrical voltage measurements across channels.

Check for DC offset at outputs first I'm thinking. Shouldn't be more than a few milivolts.
Well... I didn't electrocute myself yet... :-)

Anyway, was able to power the unit up with the main board demounted so the access to the other boards is possible. Measured the two "rails" for each side. Basically, they were each about 61.75 / -61.75v (with some "drift"... up to .8) "unloaded" (ie. nothing connected to the input or output terminals). The nominal voltage for the rails is 60/-60v.

It would appear that the rails are good.

Doing some diode mode testing on the output boards didn't find any differences between the sides although without demounting the output transistors, it would not be possible to find an open circuit since they are connected in parallel. There were no shorts per se.

I haven't done any testing on the main board yet. Looks like maybe the problem lies in the "pre section" of the main board for that side possibly although still wondering why such a big difference in the resistance measurement of the capacitor across the output for each side.

Last edited by budwich; 05-21-2019 at 08:05 AM..
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