Question Only one channel - Scrap or mendable?

michaelmorris

Member
Jun 12, 2020
2
0
20
I'm selling my old 1970s hi fi that hasn't been used in years. I have a Rotel RA 312 amp, but only one output channel seem to work. Before I stick it on eBay as spares or repair, are there any simple quick checks I can do to see if it's s simple fix ?
Thanks
 

Gray

Well-known member
...are there any simple quick checks I can do to see if it's s simple fix ?
Thanks
Once you've done all those external checks - (not least the speaker fuse on the back!!):
With the cover off have a good visual check around for obvious signs of problem.
You've got plenty of switch and control contacts that are a prime candidate for the contact spray Clark mentions:
Finally, if you've got a meter and you're happy to SAFELY probe around while it's powered up - you've got a handy working channel to compare with your dead one when measuring DC voltages.
The working channel can also be used to trace or inject audio in the dead one to narrow down your fault location.
If nothing else though, WITH THE AMP ISOLATED FROM THE MAINS try that contact cleaner, repeatedly switching and rotating after spraying inside switches and controls - there's likely to be a simple cure.
 
Last edited:

michaelmorris

Member
Jun 12, 2020
2
0
20
Thanks for all the great feedback. I've tried all the options on the check list with no luck.
I do have few observations.
1 - a pair of headphones plugged into the amp work fine with both channels working fine and the balance control smoothly fading from one side to trhe other.
2 - the amp has two sets of speaker outputs and the problem is present on the left channel of both sets
3. - the fuses to both speaker sets look fine
4 - whilst the balance control works fine on headphones, it makes no difference to the volume on the one working speaker when faded from side to side.
I guess my next step is to open it up and try the contact spray.
 

Gray

Well-known member
Thanks for all the great feedback. I've tried all the options on the check list with no luck.
I do have few observations.
1 - a pair of headphones plugged into the amp work fine with both channels working fine and the balance control smoothly fading from one side to trhe other.
2 - the amp has two sets of speaker outputs and the problem is present on the left channel of both sets
3. - the fuses to both speaker sets look fine
4 - whilst the balance control works fine on headphones, it makes no difference to the volume on the one working speaker when faded from side to side.
I guess my next step is to open it up and try the contact spray.
Worth confirming the fuse is actually OK. If you haven't got a multimeter, swap fuses between channels.
(Whilst the spray works wonders on intermittent / crackly signal switches and controls, the fact that you've both channels on headphones suggests spray is not going to be the answer for you).
 

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