NAD 7140 faint Sound, volume and tone and balance do nothing
- Thread starter marcthisdate
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- nad 7140
marcthisdate
Where’s the confounded bridge?
Took it apart, pried the cover off the relay. Both reeds engaged and disengaged. I cleaned the contacts just to be on the safe side. Nothing has changed.. Same issue remains.
marcthisdate
Where’s the confounded bridge?
No luck, but thanks for the suggestion.
FWIW, I had the same receiver and it came to me with the same issue. Turns out it was a cracked trace on the main board.
TRY THIS AT YOUR OWN RISK!
I diagnosed it by gently pressing on the main board with the unit turned on and very little volume. When I applied pressure to the correct spot the main board bowed down slightly and forced the cracked trace to make contact on both sides of the break. I was not visible to (my) naked eye but I was able to locate the break and fix it with a little solder.
Sold it to a buddy for a bottle of medium quality whisky and it's still going strong. I think these NADs punch well above their weight class and are worth keeping alive.
Nate
TRY THIS AT YOUR OWN RISK!
I diagnosed it by gently pressing on the main board with the unit turned on and very little volume. When I applied pressure to the correct spot the main board bowed down slightly and forced the cracked trace to make contact on both sides of the break. I was not visible to (my) naked eye but I was able to locate the break and fix it with a little solder.
Sold it to a buddy for a bottle of medium quality whisky and it's still going strong. I think these NADs punch well above their weight class and are worth keeping alive.
Nate
marcthisdate
Where’s the confounded bridge?
Well, worth a shot so gave it a try. All boards cause you never know. Regretfully, nothing changed.
elnaldo
Lunatic Member
Did you narrow the problem to the Preamp or Power amp?
If you connect to the AUX in, and send the signal from the PRE-OUT to a second amplifier, are both channels working? That means the preamp section is OK.
If connecting a source to the MAIN-IN, and one channel is missing, that means the problem is from that point to the power amp, or the power amp itself.
If you connect to the AUX in, and send the signal from the PRE-OUT to a second amplifier, are both channels working? That means the preamp section is OK.
If connecting a source to the MAIN-IN, and one channel is missing, that means the problem is from that point to the power amp, or the power amp itself.
marcthisdate
Where’s the confounded bridge?
I don't have a second amp to test the preamp on. Could I assume this would not work if I plug the preamp into another receivers aux jack? Would a meter on the outputs of the preamp work to test for output or is the output too low to measure?
The amp is definitely not well on one channel, that I have verified.
elnaldo
Lunatic Member
You can send the pre-out to a second receiver AUX input. just keep the volume low and start increasing so you don't saturate the 2nd amplifier input.
Anyway if you already connected directly to the MAIN-IN and one channel is missing, the problem is at the power amp half. I'd guess the PRE-OUT has both channels working.
Anyway if you already connected directly to the MAIN-IN and one channel is missing, the problem is at the power amp half. I'd guess the PRE-OUT has both channels working.
marcthisdate
Where’s the confounded bridge?
Connecting directly from the preamp into the aux of my 2225. Except for a slight hum, no sound from the preamp was audible...
elnaldo
Lunatic Member
hmmm that's not OK.
No sound, or just one channel? Make sure everything is properly set, "tape monitor", "function selector", whichever switch could stop the signal. But at least one channel should sound, the same channel you hear with the MAIN IN in the unit in question.
I find weird that a channel failed in the preamp AND in the power amp sections...
No sound, or just one channel? Make sure everything is properly set, "tape monitor", "function selector", whichever switch could stop the signal. But at least one channel should sound, the same channel you hear with the MAIN IN in the unit in question.
I find weird that a channel failed in the preamp AND in the power amp sections...
marcthisdate
Where’s the confounded bridge?
Agreed on the weird. The preamp produces no sound on either channel, the amp just sound on one side when I disconnect the jumpers and feed a signal directly to it...
elnaldo
Lunatic Member
If one channel sounds through the power amp, that signal is coming out of the preamp, and should be present if you send it to a 2nd amplifier.
If you can, open the cover and take a look, perhaps somebody jumped the connections inside.
Also, try your amplifier without the jumpers. Some units have internal connections so that jumper is not needed, or sometimes the PRE-OUT to the MAIN IN is connected inside the unit with wires.
If you can, open the cover and take a look, perhaps somebody jumped the connections inside.
Also, try your amplifier without the jumpers. Some units have internal connections so that jumper is not needed, or sometimes the PRE-OUT to the MAIN IN is connected inside the unit with wires.
marcthisdate
Where’s the confounded bridge?
I only hear the one channel from the amp with the jumpers disconnected and a second sound source, my iPod, connected to it. The preamp appears to be audibly dead.
elnaldo
Lunatic Member
OK: I thought you had one channel working 100%.
After trying the simper things (cleaning, tapping on the PCB, checking wiring) you'll need a deeper diagnosing.
If you want to fix it yourself, I suggest you to check supply voltages reaching the preamp boards, and then to build the signal tracer probe posted in post #12, and following the schematic, check where the signal is lost.
After trying the simper things (cleaning, tapping on the PCB, checking wiring) you'll need a deeper diagnosing.
If you want to fix it yourself, I suggest you to check supply voltages reaching the preamp boards, and then to build the signal tracer probe posted in post #12, and following the schematic, check where the signal is lost.
marcthisdate
Where’s the confounded bridge?
Thanks to everyone who helped. Really appreciated. I decided to abandon the diy aspect of this project as I feel like I’m in over my head so brought it in to a local shop this morning. I’ll update this thread when I get the diagnoses back.
marcthisdate
Where’s the confounded bridge?
Coming back to this thread to update. Just got it back from the shop. For the amp section, turned out the power supply needed to be recapped and a number of solder joints reflowed or redone. The tuner was crippled by a defective micro processor which was sourced from a carver unit. Turns out they use the same chip. Price to fix was reasonable and really happy to hear it sing...
Okke 70s
Super Member
That is surely not a thing to trow in a basket!
Have you checked the power supply coming in to the pre-amp properly? And if the voltage is okay, maybe move on to the first capacitor.
marcthisdate
Where’s the confounded bridge?
I agree, definitely worth salvaging and I did end up getting it fixed. Good call on the power supply issue as it was a mix of bad power supply caps, microprocessor failure and solder issues. I'm listening to it as I type this and I am very glad I had it serviced. Its not overly bright, probably closer to my Marantz 2225 in sound with a minimalist ascetic that I really like.
