Quote:
Originally Posted by ms660
Battery operation....Bias is supplied from the battery to turn on T10 via switch contacts 14&15 on the 12/24 volt input socket assembly>>>the on/off switch contacts>>>K4 switch contacts (on record) or contacts 37&38 of S1 (on playback)>>>contacts 5&6 of S1002>>>R79.
Mains operation....Bias is supplied from the regulator T606>>>contacts IV&VI (mains unit aka Z131 inserted)>>>the on/off switch contacts>>>K4 switch contacts (on record) or contacts 37&38 of S1 (on playback)>>>contacts 5&6 of S1002>>>R79.....
….Also from the regulator T606>>>R81>>>R79 when contacts 5&6 of S1002 break....So far as I can make out.
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You have a great gift (and patience) for making out blurry diagrams, Lawrence! That tallies with my tracing with the meter, but put rather more clearly than the scribbles in my book!
However, that makes it weirder that there isn't anything wrong with the circuit - I've just done a Circuit Lab model of the switch and T10 and it agrees the lamps are lit for both positions of the switch.
1014 will always be at 9.5V as it comes off the same rail whether batteries or mains are connected. 1013 is 7.6V having only the 2.2k resistor between it and the 1014 jumping off point on board 600.
In this state, with the switch off, there's current flow across T10 (because there's always a voltage at the base, so the NPN 'switch' is on?) There should of course be zero until S1002 is closed to turn the lights on.