I have a curious problem with a 30+ year old NAD 3140 integrated amp.
Power switch on and panel lights glow, speakers give a thump, normal signs of life. But no signal. can hear very faint input source with volume cranked up but no amplification until the power switch is turned off..and then, normal amplified signal is heard but dies away as capacitors drain.
Any ideas? Power switch?
Thanks in advance !
Dave Rettew
Power switch on and panel lights glow, speakers give a thump, normal signs of life. But no signal. can hear very faint input source with volume cranked up but no amplification until the power switch is turned off..and then, normal amplified signal is heard but dies away as capacitors drain.
Any ideas? Power switch?
Thanks in advance !
Dave Rettew
Wouldn't be my first suspect if the power lights are on.
Check the rails (and to the preamp). It sounds more like a common derived bias voltage for the two channels is incorrect and passes through a working point as the rails collapse. Interesting fault... shouldn't be to hard to pin down but it needs measurements.
Check the rails (and to the preamp). It sounds more like a common derived bias voltage for the two channels is incorrect and passes through a working point as the rails collapse. Interesting fault... shouldn't be to hard to pin down but it needs measurements.
There is no amplified signal on turn on, just on shut down. The protection circuit kicked in a few times intially but does not kick in anymore.
Un amplified signal can be heard faintly in both channels with the volume control at 100%.
I have rebilt a few tube amps and can work safely but am learning as I go, seeing most things for the first time....I appreciate simple troubleshooting advice and probably won't follow more complex ideas just so you know where I am.
Dave
Un amplified signal can be heard faintly in both channels with the volume control at 100%.
I have rebilt a few tube amps and can work safely but am learning as I go, seeing most things for the first time....I appreciate simple troubleshooting advice and probably won't follow more complex ideas just so you know where I am.
Dave
I tend to not think both channels have the same problem, so I look to something they share.
Sorry, but you don;t have the mute button on do you? My first thought is a mute circuit hanging up.
Isolate the problem. The block diagram seems to say there is a preamp out jack and a couple power amp in jacks. So with the amp running and showing the silent symptom, plug a signal into the power amp in jack, anything come out the speakers? Likewise put a signal into one of the source jacks, and set the controls as you would, then monitor what comes out the preamp out jack. Those two tests should tell usw which half of the amp has the problem.
Elektrotanya has the schematic, though some of the scan is poor. When you get to their page, look just under the cover image and it says "processing". Wait 30 seconds until it changes to "Get Manual" and then click there. All those big green DOWNLOAD buttons are for other stuff.
NAD 3140 Service Manual free download, schematics, eeprom, repair info for electronics
Sorry, but you don;t have the mute button on do you? My first thought is a mute circuit hanging up.
Isolate the problem. The block diagram seems to say there is a preamp out jack and a couple power amp in jacks. So with the amp running and showing the silent symptom, plug a signal into the power amp in jack, anything come out the speakers? Likewise put a signal into one of the source jacks, and set the controls as you would, then monitor what comes out the preamp out jack. Those two tests should tell usw which half of the amp has the problem.
Elektrotanya has the schematic, though some of the scan is poor. When you get to their page, look just under the cover image and it says "processing". Wait 30 seconds until it changes to "Get Manual" and then click there. All those big green DOWNLOAD buttons are for other stuff.
NAD 3140 Service Manual free download, schematics, eeprom, repair info for electronics
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