Intermittent left channel

[TomJS]

Hello,

I have a problem with my NAD 3400, sorry it's not a tube amplifier. But the problem is confusing me quite a bit. The left channel is intermittent swapping speakers didn't transfer the problem so the problem is in the amp. It's like there is a connection that not completely good because it works then it starts going intermittent and sometimes even almost completely goes away and intermittently lets some signal trough. But what I don't understand is first I thought it was my A/B Speaker switch because every time I press the button it goes away for a bit so thought okay my A speak switch is intermittent so I switched the speakers to output's B but its still doing the same thing. Do you guys have any suggestions? It's not the EQ bypass switch either and I don't think it's any of the pots. But the thing that's confusing me is that it goes away after pressing the speaker A or B button. I really do want to repair this amplifier since it's a beast of an amplifier very tight in the low end and it doesn't color the sound at all.

Thanks and regards,

Tom Siemerink

Edit: switching the pre amp to mono doesn't help either and it does it on all the inputs, CD, AUX, Tuner and Phono.

[Lauri]

My guess is one of the relays before speaker connectors isn't working properly.

[Stevem]

Well things don't fix themselves, so really what choice do you have?

[TomJS]

Well things don't fix themselves, so really what choice do you have?

No okay, but since I'm not that experienced yet with amp's I was asking you guys on things I should check that are suspect.

[TomJS]

My guess is one of the relays before speaker connectors isn't working properly.

Thanks, is there any way I can check the relays? And like I said since I'm new at this stuff and this is quite a gigantic amplifier could you name the location of the parts on the schematic? And do relays have specific values I should be looking out for? Only if you have the time though! I appreciate it very much!

Thanks and regards,

Tom Siemerink

Also this is a link to the service manuals if it helps https://www.vintageshifi.com/repertoire ... Manual.pdf

[TomJS]

Also would this work? [youtube]https://www.youtube.com/watch?v=zqQUEiQgMDA[/youtube]

[Lauri]

Looking at the schematic both A and B speaker connections have their own relays. If you have the same problem with both A and B outputs then the fault probably isn't in the relays but somewhere else in the amp. Unless both of the relays just happen to have the same fault. But anyway you could try to pop the covers off the relays and spray some contact cleaner there and see if it helps. The relays are most likely located close to the speaker connectors.

Does the headphones output work normally?

[TomJS]

Looking at the schematic both A and B speaker connections have their own relays. If you have the same problem with both A and B outputs then the fault probably isn't in the relays but somewhere else in the amp. Unless both of the relays just happen to have the same fault. But anyway you could try to pop the covers off the relays and spray some contact cleaner there and see if it helps. The relays are most likely located close to the speaker connectors.

Does the headphones output work normally?

I tested headphones, they work normally. I don't know why it hasn't done it before but when I was testing the headphones, suddenly the right channel is doing what the left channel was doing. The left channel was working normally when testing but I didn't test for too long so I suspect the left channel still does the same thing but it just didn't appear in my 40 seconds of testing could be that that's because I'm still running the speakers of of the channels B right now. Sorry I can't really test longer than that right now since I've got 2 tests tomorrow and 1 the day after that so I have to learn. I'm getting quite confused by this amplifier. Since I've had the intermittent left channel problem for quite while but sometimes it would function normally for an hour or 2 but it's become more frequent lately.

[TomJS]

I'll check the relay's this weekend if I have time!

[TomJS]

In the partsheet it does say that the headphones have a different relay right?

A 81-622-1-0 RY001, 002. RELAY, MR72, SPEAKER

A 81-628-0-0 RY003 RELAY, MRSZSR, PHONES

[Lauri]

Headphones output looks like to be just series resistors from the speaker outputs to its own relay to a stereo jack. So if the headphones output works I'm back to my first guess that the speaker protection relays are faulty.

[TomJS]

Headphones output looks like to be just series resistors from the speaker outputs to its own relay to a stereo jack. So if the headphones output works I'm back to my first guess that the speaker protection relays are faulty.

Do I need to desolder the relays to take off the cover?

[Lauri]

Usually in amps like that there's enough room there to get the relay cover off in one piece without having to desolder the whole thing off the pcb.

[TomJS]

Okay so I'm pretty sure this is one of the relay's, I had to take it out but it turned out its epoxy'd shut but there are 2 small holes 1 on top and 1 on the bottom where I sprayed contact cleaner in them so let's hope that helps! Here are a few images of the part!

IMG_1641.jpg

IMG_1642.jpg

IMG_1643.jpg

[TomJS]

Is my soldering job okay? This is my second time really soldering circuit boards.

IMG_1644.jpg