11 Oct
2015
11 Oct
'15
10:23 a.m.
I'm slowly coming to terms with the schematic but I'm not quite clear where
these two voltages are being generated. I note from the block diagram that
the +15 and +12 are rectified on the motherboard (backplane) -- which
should make it GREAT fun to probe. So it looks like some careful
disassembly is now required (unless there's a trick to probing things on
the backplane...)
I will give page references as for the .pdf of the printset on bitsavers.
The bias supply is a switcher. On page 162, T1 is the chopper transformer,
D6 the output-side rectifier, C3 the smoothing capacitor
On page 168 (Bias/Interface PCB) Q1 is the chopper transistor, E2 (555) the
control oscillator, etc.
E1 on page 167 produces 5V from the 12V supply, but if the latter is missing it
can't do a lot. Get the 12V back first.
-tony