BeoMaster 1200 quiet channel help

Hello,

Acquired another BeoMaster 1200 (in white) on eBay for a snip, a chap was selling it for his grandfather knowing wasn't just junk. It was untested but did power up when plugged in.

Got it home and connected up but alas issues!

Opened it up to find a custom repair which bypassed the power switch (seemingly due to the missing return spring in the mechanism!). Also the power kept cutting out.

Sound wise there's no hum or buzz but the left channel is very quiet and seemingly unaffected by the bass/treble sliders.

I replaced the bottom half of the 1200 with one from a donor which sorted the power cutting out but still the left channel issue remains.

I switched the yellow/green wires to the preamp pcb and the issue switched channels.

Not being very experienced in electronics I'd appreciate any advice on how I can get to the root of this problem. It's a beautifully designed object and I'd love to get it working fully again!

Could be as simple as a bad volume potentiometer.

Martin

Or a faulty output capacitor.

Thanks Dillen/Beobuddy

When I switched the connections the issue moved to the opposite speaker so would assume the volume sliders are ok.

Which caps are the output ones? Are they the pair of large ones by the headphone socket?

When I was poking around with my multimeter (in an amateurish way!) I measured the voltage across one of the transistors in the right channel that sounds fine and the left channel that doesn't. The left channel was around 33v as opposed to around 14v for the working channel. Does this shed any light?

Cheers

If the problem remains with a complete replacement bottom half from a working Beomaster, the output caps, power
supply and amplifiers can be ruled out.
My money is still on the volume potentiometer.  

Martin

Thanks Martin

Is the likelihood that the volume slider has failed and need replacing or can it be repaired?

Currently the volume still increases/decreases but just at a much reduced level. The tone controls don't appear to affect the sound at all.

Is the problem on all signal sources (FM/Tape ..) ?
Check the ribbon cable, it becomes brittle with age and I've seen them fail a couple of times.

Martin

Yes - the same with all input sources. Hmmm

Check the level switch at the rear by the DIN sockets.
Give it a shot of contact cleaner (if you have) and switch it back and forth a couple of times.

Martin

Thanks Martin - will give this a go at the weekend (my fiddling time!)

Regarding the set of replacement electrolytic caps you sell, does this include all the large caps for the power supply as well? (the 3000 uF ones)

Regards

David

The service kit includes electrolytic caps, tantals,

trimmers, lamps and also the power supply and output caps.

Martin

Well I finally got the 1200 repaired - turns out it was a hairline fracture on the leg of a transistor in the pre amp. All ship-shape now so just waiting to decide where to use it now!