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Old 7th Jan 2021, 10:37 pm   #93
Boulevardier
Octode
 
Join Date: Sep 2017
Location: Bristol, UK.
Posts: 1,642
Default Re: Grundig TK20 and Truvox R82. Help Required Please.

I think you are misinterpreting that zero reading. On a DMM, a display reading of "0" means zero resistance = a short circuit, not an open circuit. So, it depends what you mean by a "big,fat zero"! It's possible that the head has an internal short, but relatively unlikely.

I've been looking back through the thread, and see that you say there is a very low-level signal present from the tape. I'm pretty sure this would not be possible if the head was completely open circuit, though it could have a partially-shorted/open winding..

Time to investigate the wiring and switching between pin 9 and the head. It's possible that a short circuit somewhere there would cause these symptoms (even a short-circuit in the wiring will have some tiny resistance, and that small resistance might be low enough to show as zero ohms on a meter but still have enough signal voltage across the resistance for a very sensitive playback amplifier with a high input impedance to reproduce it at the low level you mention). At this point the hum is a bit of a mystery, but could result from an earthing problem that may also be to do with the head switching and wiring - and the problem might be a very simple one. It's possible that one of the sections of S1 isn't working properly, or isn't earthed where it should be.

So, I suggest that you look at those areas tomorrow. Also, look especially for any disturbed wiring/connections, and for dodgy-looking earth connections. I don't know the machine, but you may find that getting to the areas in question (head wiring and switches, etc) may mean a bit of dismantling.

Mike
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