Hi Everyone,
I have a NAD C320BEE Stereo Amp, it's around 15 years old, sounds great and up until the past few weeks has been rock solid. What is happening is the left speaker output (positive terminal I think based on the wiggle test) will intermittently cut out, or sometime slowly fade until it's out. Sometimes, a wiggle of the left positive connector brings it up, other times it does not. Of course I have swapped speaker cables (banana plugs) and speakers and all that logical troubleshooting, same issue.
I am fairly comfortable trying to troubleshoot along the circuit path, maybe, if someone had some idea of where to start, or what I should be looking for. I have access to a scope and meter and all that stuff. I do have the service manual for the amp with circuit diagrams and can share/post them if that's allowed(?)
Thanks for looking and for any help!
I have a NAD C320BEE Stereo Amp, it's around 15 years old, sounds great and up until the past few weeks has been rock solid. What is happening is the left speaker output (positive terminal I think based on the wiggle test) will intermittently cut out, or sometime slowly fade until it's out. Sometimes, a wiggle of the left positive connector brings it up, other times it does not. Of course I have swapped speaker cables (banana plugs) and speakers and all that logical troubleshooting, same issue.
I am fairly comfortable trying to troubleshoot along the circuit path, maybe, if someone had some idea of where to start, or what I should be looking for. I have access to a scope and meter and all that stuff. I do have the service manual for the amp with circuit diagrams and can share/post them if that's allowed(?)
Thanks for looking and for any help!
If it genuinely fades out (as in like turning down the volume progressively) then that is an unusual problem to say the least.
I would begin by just concentrating on your 'wiggle test'. Take the board out and look over all the soldering particularly in the areas around the sockets and also any parts connected to the heatsinks like output transistors.
Speaker relays are a very common cause of problems typically giving low distorted sound that seems to correct as you turn up the volume. Try tapping it when the problem occurs.
And use the scope of course. Check the signal output direct at the amplifier output and before the relay when the problem occurs.
I would begin by just concentrating on your 'wiggle test'. Take the board out and look over all the soldering particularly in the areas around the sockets and also any parts connected to the heatsinks like output transistors.
Speaker relays are a very common cause of problems typically giving low distorted sound that seems to correct as you turn up the volume. Try tapping it when the problem occurs.
And use the scope of course. Check the signal output direct at the amplifier output and before the relay when the problem occurs.
It does seem to point to the relay contacts. If tapping the relay doesn't obviously affect the problem, 'easiest way to check without dismantling the relay, is to identify the corresponding amplifier channel output trace or lead to the relay and its correct red (+) Right or Left speaker terminal.
Bridge them with a decent, insulated clip lead or similar, ensuring you have the correct speaker for the relay terminal and make no other accidental shorts or use dodgy, oversized clips that may slip off and contact other circuits. That channel will probably "thump" when you power-on because of the direct connection but it won't hurt a respectable loudspeaker.
There is a service manual for more clarity and details here:
Bridge them with a decent, insulated clip lead or similar, ensuring you have the correct speaker for the relay terminal and make no other accidental shorts or use dodgy, oversized clips that may slip off and contact other circuits. That channel will probably "thump" when you power-on because of the direct connection but it won't hurt a respectable loudspeaker.
There is a service manual for more clarity and details here:
thanks for the replies, with more troubleshooting, it absolutely does fade out and back in sometimes alongside just cutting out. Interesting, just shifting or lifting the amp slightly from the front will bring the sound back. I think my initial wiggle test of the connector may be suspect as lifting the amp more reliably brings the sound back than jiggling connectors...
Unusual but that does sound like a dry somewhere. Look for any low voltage auxiliary rails that apply to just the faulty channel (maybe a zener and resistor that runs hot) and check the joints.
It is often more satisfactory to reflow the whole board if you can't see anything obvious.
Look for cracking around joints as in the last pictures in post #1 here:
Sony CDP790 and KSS240 Restoration Project
It is often more satisfactory to reflow the whole board if you can't see anything obvious.
Look for cracking around joints as in the last pictures in post #1 here:
Sony CDP790 and KSS240 Restoration Project
going to tentatively say it's fixed, cleaned the relay, and re-soldered some of the joints around that part of the path (not sure if they really needed it but oh well). Hasn't cut out or faded in a couple hours of playing.
Thanks everyone for your help!
Thanks everyone for your help!
well done.