Hi there!
Short background:
I'm new on this forum and also quite new to vintage audio. A year ago I bought a NAD 319 in fairly good condition. More recently I have also bought a cheap NAD C370. Both are experiencing some issue at the moment and I would like to try and repair it myself. Hopefully you can help me!
NAD 319 - Partial power on after re-cap
After one year of happy listening, my NAD 319 starting fading on the right channel. This happened over the course of two weeks until almost no sound was coming from it. I figured it had to do with the caps on the PSU board so I replaced all of them. Now it turns on, but no power comes on the tone control and volume control board. I can hear the relay clicking though.
NAD C370 - Loud turn-on thump / pop
My other amp has all of a sudden the amp started to produce a loud pop on the left channel when I turn it on or off. Some pop was already there, but it was very soft and seemed normal.
The pop stays when I plug in a headphone jack.
If you can help me troubleshoot it would be great! Happy to provide more answers or photo's if necessary.
Thanks in advance.
Cheers,
Shiftie
Short background:
I'm new on this forum and also quite new to vintage audio. A year ago I bought a NAD 319 in fairly good condition. More recently I have also bought a cheap NAD C370. Both are experiencing some issue at the moment and I would like to try and repair it myself. Hopefully you can help me!
NAD 319 - Partial power on after re-cap
After one year of happy listening, my NAD 319 starting fading on the right channel. This happened over the course of two weeks until almost no sound was coming from it. I figured it had to do with the caps on the PSU board so I replaced all of them. Now it turns on, but no power comes on the tone control and volume control board. I can hear the relay clicking though.
NAD C370 - Loud turn-on thump / pop
My other amp has all of a sudden the amp started to produce a loud pop on the left channel when I turn it on or off. Some pop was already there, but it was very soft and seemed normal.
The pop stays when I plug in a headphone jack.
If you can help me troubleshoot it would be great! Happy to provide more answers or photo's if necessary.
Thanks in advance.
Cheers,
Shiftie
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First download the service manuals.
NAD 319
If you have signal generator (or sound card with signal generating SW) and oscilloscope, you can follow the input signal until it disappears. The fault is in the section where the signal is gone. If you don't have at least a signal generator and oscilloscope, then it can be difficult to repair.
Double check the solder joints you made. Check that all connectors that you may have disconnected are properly connected, e.g. no connector pins were bent accidentally. Check the supply voltages going to the small signal sections.
NAD C320
we should see the service manual for the schematic.
NAD 319
If you have signal generator (or sound card with signal generating SW) and oscilloscope, you can follow the input signal until it disappears. The fault is in the section where the signal is gone. If you don't have at least a signal generator and oscilloscope, then it can be difficult to repair.
Double check the solder joints you made. Check that all connectors that you may have disconnected are properly connected, e.g. no connector pins were bent accidentally. Check the supply voltages going to the small signal sections.
NAD C320
we should see the service manual for the schematic.
Hi Gerenis,
Full service manuals:
NAD319
NADC370
I don't own a signal generator nor an oscilloscope. Can I do something with my Multimeter?
I will check all the connectors and verify that there is indeed no power on the volume control, front panel and led boards. Both amplifier sections are powered, so the problem must be somewhere else.
Thanks for your suggestions
Full service manuals:
NAD319
NADC370
I don't own a signal generator nor an oscilloscope. Can I do something with my Multimeter?
I will check all the connectors and verify that there is indeed no power on the volume control, front panel and led boards. Both amplifier sections are powered, so the problem must be somewhere else.
Thanks for your suggestions
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Sorry, turns out it's a NAD C370 and not C320. I've updated my posts.
Regarding the thump / pop at turn on i've noticed the following:
- Plugging in a headphone jack won't help
- The thump is there even with the main and pre-amp disconnected
- It seems that the protection relay switches on very fast (~0.5s after turning on).
I remember from my 319 that this should take around 2s to prevent this thump. Could it be that a cap is old? Which one should i check?
Regarding the thump / pop at turn on i've noticed the following:
- Plugging in a headphone jack won't help
- The thump is there even with the main and pre-amp disconnected
- It seems that the protection relay switches on very fast (~0.5s after turning on).
I remember from my 319 that this should take around 2s to prevent this thump. Could it be that a cap is old? Which one should i check?
I repair most problems with a DVM (for DC) plus an analog VOM to trace music through the signal paths. Cheap DVM produce random number on music with the AC scale, as this is designed for power line frequency only. $160 RMS dvm ignore problems like ultrasonic oscillation over 7 khz. I view these devices as useless because of this blind spot. VOM will show high steady value on oscillation, which looks nothing like the bobbing pointer of rock music or announcer speech.
My VOM has 2 vac and 20 vac scales and 5000 ohms/volt sensitivity. The advantage of the VOM is that is doesn't have 150 electrolytic caps in it, and has lasted 34 years without repair. Scopes 15 years newer have become useless due to the e-cap problem. Also if I step on the VOM probe it costs $6, not $50.
The AC scale of the VOM requires a .047 uf cap series the ground probe (with clip leads) to avoid showing AC readings on DC voltages. Max voltage cap higher than max voltage of the product under repair. I use 400 v.
For a signal generator I use a pocket radio I salvaged from the trash at work and replaced the volume pot on. Most of these also have a dirty battery clip. A earphone jack to dual RCA plug cable is required, also some times 2 RCA jack to 1/4 phone plug adapters. Turn the earphone volume down, most radios will put out 7 vac max and line level inputs go full volume at 1.6 vac or 2 vac.
Sounds as if you have a DC problem on the popping unit, detectable with the DVM. The protect circuit has 4 electrolytic caps, down in the lower right of your schematic. I'm not familiar enough with the UPC1237 to determine which is the cause of your too-quick turn on of the relay. Because it is directly connected to the power supply, I'd guess C764.
Note when replacing e-caps is is advantagous to test the unit after the cap is replaced, to see if you made the problem better, or worse. Amateurs make a lot of bad solder joints, sometimes put e-caps in backwards, and sometimes put the wrong value in. If the unit gets worse after changing one cap, you know right where the problem it - what you just did.
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What is the meaning of VOM?
Volt-Ohm-Milliammeter
VOM or Vom may refer to: VOM = Volt-Ohm-Milliammeter, another name for a multimeter.
Volt-Ohm-Milliammeter
VOM or Vom may refer to: VOM = Volt-Ohm-Milliammeter, another name for a multimeter.
VOM in the US applies to both digital and analog devices.
As noted in post 5, I've found $30 Sears & Farnell DVM produce random numbers on sine waves other than 50 or 60 hz. Analog meters with 20 vac scale that are quite useful for tracing VAS & later go as low as $30 on ebay. The DVM averages over 2 to 4 seconds also, whereas an analog meter pointer will dance to the beats of rock music. My Simpson 266 analog VOM with 2 vac scale was about $200 in 1986, but used ones are cheaper.
I put about 10 e-caps in a b&K 2120 scope to make the sweep work, but I still don't have room on my coffee table for it plus the device under test. Nor do I have $100 of hhsmith probes since the burglar carried off nearly everything electronic 9/14/20. The Simpson 266 & the 2120 were beneath his dignity to load up, but the working DVM's are gone. The advantage of DVM's, they will show both plus and minus DC voltages without changing scales or moving the return alligator clip to the other probe.
As noted in post 5, I've found $30 Sears & Farnell DVM produce random numbers on sine waves other than 50 or 60 hz. Analog meters with 20 vac scale that are quite useful for tracing VAS & later go as low as $30 on ebay. The DVM averages over 2 to 4 seconds also, whereas an analog meter pointer will dance to the beats of rock music. My Simpson 266 analog VOM with 2 vac scale was about $200 in 1986, but used ones are cheaper.
I put about 10 e-caps in a b&K 2120 scope to make the sweep work, but I still don't have room on my coffee table for it plus the device under test. Nor do I have $100 of hhsmith probes since the burglar carried off nearly everything electronic 9/14/20. The Simpson 266 & the 2120 were beneath his dignity to load up, but the working DVM's are gone. The advantage of DVM's, they will show both plus and minus DC voltages without changing scales or moving the return alligator clip to the other probe.
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Thanks Idianajo for your replies. I will try and follow the signal until it dissapears and let you know.
The popping unit I think might have something to do with a worn E-cap in the protection circuit. I will see if I can replace those units to solve the issue.
Keep you posted!
The popping unit I think might have something to do with a worn E-cap in the protection circuit. I will see if I can replace those units to solve the issue.
Keep you posted!