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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 1st Sep 2022, 10:39 am   #1
60 oldjohn
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Join Date: Dec 2004
Location: East Yorkshire, UK.
Posts: 3,958
Default Roberts, RT1

I switched the set on after a few years of inactivity and was greeted with a loud hiss/ buzzing sound not a station heard. Then I realised the volume control was set low. When I raised the volume, stations could be heard above the constant level of noise.

So the fault must be after the volume control, possibly a noisy transistor or resistor. The driver transistor was an OC71 which are not beyond suspicion at 64 years old. And the output are a pair of OC72. I sprayed the OC71 with freezer spray and the level of noise dropped a bit. Before I remove it I put my signal tracer on B then E of the OC71 Driver clear, no noise, then on to pin C and was "rewarded" with a loud noise. I replaced it with a NOS OC71, which worked well, but I am aware these glass transistors can fail by going noisy. It tested as 2 Diodes.

John.
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