NAD 7240pe - No sound through right channel

[Newbie999]

Hi everyone

I'm sure you've seen a hundred of these but here goes. Any help greatly appreciated.

I've just bought a second hand NAD 7240pe. The seller informed me it was in full working order last time it was set up however has been stored under cloth and unused for a while. I am getting audio in the left channel (a+b) but nothing on the right (a+b). I have tried both speakers (bananna plugs) across the left channel in both a and b and they both work. However putting them both in the right channel produces no audio whatsoever. Before trying to take it in for repairs is there anything I could look at. I'm a novice as such with audio equipment although i can put together a PC and have replaced a channel on a mixer before.

Edit: Balance is set in the middle.

Also. I have Eltax Monitor III speakers (which i am going to upgrade soon) impedence states 4-8ohm on the back of the speakera. The back of the amp/receiver there is an impedence switch. Is it better at 4 or 8?

Thanks in advance.

 

[northpaw]

This series of NAD units seem prone to developing some oxidation on the switches and pots. A missing channel can often be brought back by application of a contact cleaner to the relevant components inside the unit (directly to the switch or pot, aimed at any openings in their cases) coupled with a thorough exercising those controls. If the amount of oxidation is slight, sometimes just exercising the controls will bring some sound back. If you have some music playing softly, you can exercise the controls (front panel only) vigorously (other than volume) to see if any one control results in some sound on the R (often it will be crackly at first, so don't be alarmed, just keep the volume relatively low). The presence of any sound on the R while doing this usually indicates the R channel is working, it just has dirty contacts that need to be cleaned.

In my experience, that balance control (a pot) is the usual culprit. But it can be the volume control and other switches on the front and rear panels. The pots are of an open type, and with the top cover of the receiver off, you can actually see the wipers on the balance and volume controls when you operate them. Give them a good shot of contact cleaner. I like the CRC QD spray, available at WalMart, usually near the auto section, as it does not leave any residue. Once things are cleaned and operating, I like to follow up with either a few DeOxit drops on the switches (regular DeOxit) and pots (the Fader variety). Sometimes you need the DeOxit stuff to cut through the oxidation, but I often find I can get it working again with just QD and exercising the controls.

Of course, it could be something other than the switches and pots, but those are the usual suspects and the easiest and cheapest to address first. But do make sure you have both the pins that bridge the Pre out–Main in jacks in the back panel (a missing R one would give your symptoms).

On the 8 vs 4 ohm switch, best to leave it on 4Ω. It just reduces the output a bit.

Be sure to check both that switch and the Soft Clipping switch in the back, and clean and exercise them (always with the unit off). Generally, other than the testing by exercising I mentioned above, on all cleaning operations, turn off and unplug the unit.

Welcome to AK.

 

[Newbie999]

Thanks for that. I've read about what you've mentioned but usually when there is at least some sound. I'll get cracking with using a contact spray to see if i can begin to get some sound out of it. If not i'll report back. I'll grab some deoxit spray as well. Many thanks for your time and response.

 

[kjello]

Cleaning all switches is a good advice, also speaker protection relays would be my second thing to check/replace.

 

[northpaw]

Normally I would agree, but in this unit there aren't any. So speakers are at risk if a failure in the outputs places rail voltage on the speaker terminals, but there are no relays to age and degrade the sound. I've never had a problem with the NADs in trashing speakers, but I am careful and try to avoid doing stupid stuff.

BTW, OP, if you don't have the service manual for the 72040PE, it can be downloaded from hifiengine.com. You have to register there, but it is free and safe. You may find the service manual helpful in getting to know your unit better. It isn't necessary to do the cleaning discussed above, but it does provide schematics, a parts list, and info on checking/adjusting DC offset and amplifier bias (idle), which may have drifted some since it left the factory.