Am servicing a Goldmund Nemesis 3. Only have the amplifier schematic, but not the schematic showing the relays.
The unit powers on, but when taking it out of standby, a relay behind the front panel chatters at 60Hz. I suspect a bad cap somewhere that drives the relay coil, but can't see anything due to the way the PCB is sandwiched as part of front panel. Does anyone know physically which capacitor is responsible for filtering the power to the relay coil?
The unit powers on, but when taking it out of standby, a relay behind the front panel chatters at 60Hz. I suspect a bad cap somewhere that drives the relay coil, but can't see anything due to the way the PCB is sandwiched as part of front panel. Does anyone know physically which capacitor is responsible for filtering the power to the relay coil?
I successfully repaired the initial problem, which was that the amp itself makes a buzzing sound when taken out of standby. That was a relay field coil chattering and the source of the problem was an open electrolytic (one of the 15kuF main capacitors) which I replaced.
Having been able to start the amplifier, I was greeted by a second problem: the amp would shut down whenever I connected anything to the left channel input. Even a shorting plug. I found that the left channel would go into oscillation at 91KHz when anything was connected to its input. I starting thinking bad ground somewhere, so I pulled the left channel module apart and discovered that the coax shield had broken off at the PCB. Repaired that and the amplifier started to work normally. Called it a done repair, set it up with speakers and listened to it for two whole days. Wonderful.
Then on Day 3, I turned on the amplifier and the right channel went into protection. Put amp back on bench, disassembled and measured all the resistors and compared to good channel. All same. Measured the small signal transistors with curve tracing meter. All same as left. Powered the amp on some hours later and it worked normally again. Let run all day into dummy load. Great. Shut it off and contacted customer.
Then this evening I decided to do one last quick check. It gets even stranger. Now NEITHER channel comes out of protection when brought out of standby. The left channel is oscillating again. But ground continuity to jack is good this time. Right channel has no signal on it. Shut down power. Apply power again, wait 5 minutes for the amp's ready signal standby to come on, power on the amp. Left channel works again, but right channel has a -200mV DC offset and some minute positive peaks from test signal come through. Put amp back in standby, but left channel stays on!
This amplifier is full of gremlins. And it's living up to its name: NEMESIS. I have no schematics or documentation and this is rapidly becoming a quagmire. I'm tempted to tell customer it's not economically realistic to try to repair.
Having been able to start the amplifier, I was greeted by a second problem: the amp would shut down whenever I connected anything to the left channel input. Even a shorting plug. I found that the left channel would go into oscillation at 91KHz when anything was connected to its input. I starting thinking bad ground somewhere, so I pulled the left channel module apart and discovered that the coax shield had broken off at the PCB. Repaired that and the amplifier started to work normally. Called it a done repair, set it up with speakers and listened to it for two whole days. Wonderful.
Then on Day 3, I turned on the amplifier and the right channel went into protection. Put amp back on bench, disassembled and measured all the resistors and compared to good channel. All same. Measured the small signal transistors with curve tracing meter. All same as left. Powered the amp on some hours later and it worked normally again. Let run all day into dummy load. Great. Shut it off and contacted customer.
Then this evening I decided to do one last quick check. It gets even stranger. Now NEITHER channel comes out of protection when brought out of standby. The left channel is oscillating again. But ground continuity to jack is good this time. Right channel has no signal on it. Shut down power. Apply power again, wait 5 minutes for the amp's ready signal standby to come on, power on the amp. Left channel works again, but right channel has a -200mV DC offset and some minute positive peaks from test signal come through. Put amp back in standby, but left channel stays on!
This amplifier is full of gremlins. And it's living up to its name: NEMESIS. I have no schematics or documentation and this is rapidly becoming a quagmire. I'm tempted to tell customer it's not economically realistic to try to repair.
Cut your losses, it's not worth the aggravation. And how do you know it won't act up
again after the owner takes it home? Bad for your reputation.
again after the owner takes it home? Bad for your reputation.
Yeah, I'm of the same mind. I hate these types of repairs. I have bills to pay and wasting many hours on what started as a successful repair only to have something else go wrong, nullifies all the work I've done in those several hours. And people wonder why there are fewer and fewer repair shops still in business...