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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 15th Oct 2017, 6:05 pm   #1
yestertech
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Join Date: Dec 2002
Location: Coulsdon, Surrey, UK.
Posts: 2,109
Default REVOX G36 - solenoid supply missing.

A while ago I was given a nice G36 which worked perfectly - it was useful that the machine was 1/4 track and slower speed , So I set about copying some old R2R tapes I had found.
All was well for some weeks until there was a 'pfft' noise and a wisp of smoke appeared through the top plate.I reached quickly for the power switch to avoid further damage.
The smell emanating from where the smoke had been reminded me of 'cooked transformer' so I assumed ( wrongly, thankfully ) that the mains transformer had given out.

The machine was put way for quite a while, but I thought I ought to dig it out and assess the damage. Having powered it up slowly on the variac , by 100v all seemed quiet.

I metered through the various DC power rails and found the HT and LT ( DC heaters for preamp valve ) to be OK, but the DC supply for the solenoids and relays was absent. One input to the rectifier bridge was unsoldered as a precaution , and the input voltage increased to normal.Luckily, the electronics powered on and there was playback noise, so the transformer appears OK. ( large sigh of relief )
Without further dismantling, I can't remove the rectifier bridge either for replacement or testing, but the AC input to it seems OK. The output feeds directly into a 600uF cap and this tests OK. The bridge may have failed due to age, but oddly when I measure the DC resistance of the feed from said cap. to the relays I get just 25 ohms. This equates to around 1 amp, but it's there all the time irrespective of any function buttons being pressed. This may be normal of course, but from examining the diagram, it appears there should be no resistance here 'at rest'.

I probably need to study the switches and relays in more detail. But if anyone has one of these machines, perhaps they could comment ? Meantime I will attempt to separate the upper and lower chassis assembles for a more detailed look.

A
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