Arfa Daily wrote:
"427Cobraman" wrote in message
ups.com...
Have both a DE845 and DE945 and also have the service manual. Neither
unit will power on. The 845 had chattering power and I found
bad solder joints in the display board. After repairing those, the
unit ran for about a minute and a half then shut down...never to
restart. All fuses are good, and the standby power circuit seems to
be working fine. When pushing power button nothing happens (front
panel or remote). So, I'm assuming there is a problem with the
standby circuit. According to the schematic, the main power
x-former is off until the the standby relay is switched on, so
ruling out that area. Is there a built-in protect that prevents
unit from coming out of standby? I took voltage readings earlier
but will recheck them one I get home and post them. BUT, if memory
serves, I had 5vdc out from some terminals and 10-13V on the
collector of Q901 which supposedly powers the relay (RY901). I'm
looking for guidance on how to approach this problem. I'm
proficient with O-scope, DVOM, ESR meter, and general electronic
repair. Just never messed with audio receiver/amps before. Thanks, Alex

Very first thing is to make sure that no front panel buttons are being
accidentally pushed by slightly wrong assembly of the front panel.
Make sure that all buttons move, and click.

Assuming that there is no attempt by the main power relay to close,
when you try to turn it on, you can try forcing it, by temporarily
shorting the collector to the emitter on the relay driver transistor.
DO NOT have any speakers connected to it at this time. If unit then
appears to come up ok, check all of its display and operation
functions. If anything here seems not to be working correctly,
chances are it's a system control problem, possibly related to the
work you already did on the front pcb. If all is still looking good,
check across ALL speaker outputs for DC. If there is any, then check
power supplies to output stages carefully. Some of these big amps
monitor the power supplies, and if anything is wrong, block
operation, although that's only a potential issue if the main power
relay does close momentarily. If everything is still looking ok, you
can give it some input, and see if the outputs look normal on all
channels, on a 'scope. If this looks good, you can risk some
speakers, and then carefully recheck all functions. If there are any
noted problems, they should give you a clue as to where to look. If
it all appears to be working ok, then the only circuitry that you
then need to concentrate on, is the relay drive, back to the system
control micro, but check the circuit around the system control micro
carefully, for any pins that may have a power up blocking function.
With the standby supply present, and the system control idling, you
should be able to verify that there are no incorrect inputs to the
micro.
Arfa

Could just be the micro isn't getting any power. A regulator might have
died, a crystal might be intermittent, and I'm thinking there were a couple
1 ohm power supply resistors that would go bad on these. I'll check.

Mark Z.