So i just bought this NAD 710 amplifier for 2 bucks. It has no sound in the right channel, the left channel works fine. It also seems to have some issues in the mono mode but that's not my biggest concern since i dont plan to use it. It also produces a loud thump and hum when i turn it on. I also found two components that i cant identify that are possibly either burnt or rusted.
To summarize these are the issues:
Here are some videos of the issues:
Here are some pictures:
NAD 710 - Album on Imgur
Heres the link to the service manual.
nad_710_sm.pdf | DocDroid
I have a multimeter but no scope. Any ideas where to start?
To summarize these are the issues:
- No sound in right channel
- When mono mode is on, there is noise when adjusting the volume knob or pressing the mono mode button
- Temporary thump and humming when powering up on the amplifier
Here are some videos of the issues:
Here are some pictures:
NAD 710 - Album on Imgur
Heres the link to the service manual.
nad_710_sm.pdf | DocDroid
I have a multimeter but no scope. Any ideas where to start?
I fix amps all the time with a DVM and an analog VOM with a 20 VAC and 2 VAC scales. The analog vom is for tracing music from a pocket radio in the input. put a .047 uf >200 vdc capacitor in series with the negative probe on the VOM to keep it from reading DC on the AC scales. Use an alligator clip lead to the speaker ground.
You could check DC on the big capacitors, the rail capacitors. Use the DVM for DC voltages. Capacitors should be +- 2/3 of the rated voltage printed on the capacitor. these are voltages over 24 that could kill you, so use only one hand at a time so current doesn't cross your heart. Use a clip lead on meter negative, not your hand. Use no jewelry on hands wrists or neck, 1 v @ 30 amps can burn your flesh to charcoal. Wear safety glasses, parts can explode or solder can splash in your eye.
Typical analog VOM are on the electronic sites for about $15. Cheap DVM lie on music on the AC scale, they are only for 50-60 hz wall power. Expensive RMS DVM ($180) won't pick up ultrasonic oscillation above 7 khz, total waste of money in my opinion.
If the rail voltages are okay, put some music in the input and see how far it goes. Input jack, blocking capacitor, volume pot, connector to input board, base of input transistor (a small one, TO92 package or TO18).
I'll bet music stops somewhere up in there.
Other possible common faults, output transistors shorted by some field wiring problem. With power off, check b-e and c-e of the big transistors on the heat sink, with diode scale of DVM. On the dead channel. Should be .480 to .750 v fowards, 9999 or ---- backwards. Another likely suspect, music goes into the protection relay (if it has one) near the output and doesn't come out.
Have fun, better than crossword puzzles I think.
You could check DC on the big capacitors, the rail capacitors. Use the DVM for DC voltages. Capacitors should be +- 2/3 of the rated voltage printed on the capacitor. these are voltages over 24 that could kill you, so use only one hand at a time so current doesn't cross your heart. Use a clip lead on meter negative, not your hand. Use no jewelry on hands wrists or neck, 1 v @ 30 amps can burn your flesh to charcoal. Wear safety glasses, parts can explode or solder can splash in your eye.
Typical analog VOM are on the electronic sites for about $15. Cheap DVM lie on music on the AC scale, they are only for 50-60 hz wall power. Expensive RMS DVM ($180) won't pick up ultrasonic oscillation above 7 khz, total waste of money in my opinion.
If the rail voltages are okay, put some music in the input and see how far it goes. Input jack, blocking capacitor, volume pot, connector to input board, base of input transistor (a small one, TO92 package or TO18).
I'll bet music stops somewhere up in there.
Other possible common faults, output transistors shorted by some field wiring problem. With power off, check b-e and c-e of the big transistors on the heat sink, with diode scale of DVM. On the dead channel. Should be .480 to .750 v fowards, 9999 or ---- backwards. Another likely suspect, music goes into the protection relay (if it has one) near the output and doesn't come out.
Have fun, better than crossword puzzles I think.
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