Joined: 13 Mar 2009
|Posted: Tue Apr 06, 2010 8:10 am Post subject: YAMAHA RX-V2500 PA Problem
I hope someone can help with this:
I have a RX-V2500 on the bench with what I believe to be a strange bias problem on the SL channel output stage. DIAG mode displays DC Protect fault.
So here's the scoop -
Upon power up I read about -1.5V on the speaker output, which climbs to about -3.1V volts after about 20 seconds, then of course the DC protect kicks in and shuts it down.
I see this same -1.5V ~ -3.0V on the input to the PA (this is the "VSL" signal). It also too slowly climbs up to about -3.0.
The same voltages (-1.5V ~ -3.5V) show up on both emitters of the complementary transistor pair prior to the finals.
I replaced almost every component in the bias and output stage including the finals and .22Ohm pair. I checked for any possible floating grounds.
I also checked and rechecked components on the preamp/driver board.
The other channels are all fine.
By now I'm pulling my hair out!