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Help! Naim NAC72 lost right channel

N

nap90

pfm Member
Hi All,
I am at my wits end trying to find out why my lovely RSL 72 suddenly lost the right channel, or rather what to fix!
So Sound only Comes out of the left Speaker. I have done the following Investigation, so have no idea where further to look:
- Tried different sources, (tuner, DAC, Phono) always right Speaker quiet
- Swapped 180/hicap/72 out for a Nait 2 - all working, so Speakers OK
-Swapped Speakers left and right at NAP180 - then is left channel gone
-Swapped 180 for nap90 - same issue, so not power amp
-Powered 72 directly from 180 - same issue, so not SNAIC5 interconnect or hicap
-Tried different SNAIC4 interconnect -same issue
- swapped sequentially L/R boards inside 72 - first tape buffers, then Input buffers, then line out RSL boards and still right channel dead AAAARRRRHHH1

Can maybe a relay be shot? waggling all the wires inside, makes also no difference at all.

regards
Matt
 
all those that have are a left and a right i swapped to no effect, that is why i am so stumped!
 
I had a NAC72 quite a long time ago, that developed a similar problem. It turned out to be the input selector. The front panel input selector acts remotely on the PCB switch via a blue ribbon type device and this sometimes gets out of alignment causing the contacts not to make correctly; I seem to remember it being an easy fix.
 
To see if it is the 325 relay board, just take it out and link the relevant pins. Make sure the preamp has stabilised for a few seconds before switching the power amps on.
 
In the 72 there are several switching relays mounted on the underside of the main board. The fault could also lie with one of those.
 
Oh, that’s a good tip, thanks Nick.

Anyone any idea where to get Clare 2a12 relays in case one is duff?

Regards
Matt
 
Hey Matt ! if you swapped boards and cables and the problem is still on the same channel , it could be the switches , the relay ( that you can jump ) or volume pot ( jump using a resistor 5k ) , . try lubricating the switches also !!!
 
you could make a little audio probe using a little mini amplifier of some description (like a radio) attached to a wire with a 2pf capacitor soldered to the end - just to trace out where on the board you stop getting signal - but the first thing i would do is put some deoxit (contact cleaner) on your pots etc
 
The relays on the motherboard only switch the tape outputs.
The little 325 card can have a duff 20v zener or 47uF cap. The relay voltage then never quite gets to full potential and one reed may make while the other doesn't. Linking it out would be the next logical step.
 
Just to avoid a potential disaster, to link out a 325 board:

remove the board
number the pins 1 to 6 (it doesn't matter which end you start from)
connect pin 3 to pin 4 and pin 2 to pin 5

HTH
 
Matt,
There is one more diagnostic test you can do which might help. The RSL time-aligned boards you have kept the "mono" switching capability of the 32.5 that was dropped in the 72 unit. If you connect a jumper cable (see below) between the two Mono pins it will combine the left and right channels. If you still have a left-only output, then you know it must be the output relay that is bad. If you suddenly have output on both channels, then it must be the input selector switch. Hope this helps.

MonoJumper.JPG
 
HI All,

Thanks ever so much for your time and suggestions. So i am a leap further....

Bridging the Pins on the 325 (Thanks Piglets Dad for the instructions) brought both channels back to life, so the culprit is definately localised now to this board.

I then took the bridge wires out, swapped out the 47µF cap for a Silmic of the same value (sorry bit of a waste, i know!) i had lying around - back to left channel only.

So i guess this leaves only the relay or the diodes (there are three?)

I tried the trick with a magnet Held up to the relay - this then shut off the left channel that was working (so no Sound at all)

One further Observation that i missed earlier as i had my LP12 and it's earthing cable plugged in all the time: With only NAT01 as test source (LP12 and earth wire removed), in the cases where the right channel is silent, the Speakers buzz quite loudly. With the link wires as per Piglets Dad, all is silent. Is the because the Input to the power amp is open one one side in my case?

Regards
Matt
 
Exactly right. When the relay fails and stays open, the output side is not connected to anything. I would have put at least some kind of high valued resistor on it but Naim didn't, so you have a great hum antenna instead!
 
Ok so it's definitely down to the relay on the 525 board then.

If the relay latches on one channel then the coil works correctly when required so it's likely the relay itself.

Only "but" is if the coil voltage is under 12v due to a different issue which you can easily enough check with a meter.

It's probably been 20 years since I owned a 72 but I thought the three relays on the dark side of the Mobo did the source/tape, and mute functions so a fault in any one of them could cause the issue.
 
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