Tim Schwartz wrote in message
...
N Cook wrote:
from about 1986

1/ Bit larger than 1N4001 size and appearance, smaller than 1N5401 , a
ring
of chevrons around marks the cathode, small script 63 then large script
B4406

2/ 1N4148 size and appearance , thick blue ring denotes the cathode end
and
2 thin green rings




Nigel,

Could you tell us what the diodes are in and the location numbers?

Thanks!
Tim Schwartz
Bristol Electronics

I think I've cracked it, one of the most awkward of repair situations.
A previous er-um repairman had got there before me.
I can only assume that the previous one noticed a component populating a
pair of holes , on traces, with no corresponding overlay graphic outline or
designation and removed it as suspicious. Numerous such holes, unused and
unmarked for this model, on the pcb .
I assumed, from the disturbed solder , that he'd tried something temporary
at that point but it now looks as though there was originally a small C
there that slowed down the HV response to the LV error amp via opto coupler.
The optimum error V was about 5 minus 2.2V but it was racing over that up to
5V, as there was no capacitance in the error amp, so cutting off the OC and
forcing the HV oscillator to maximum power consumption and all error control
lost.
Now just a matter of finding the optimium, educated guess/suck it and see,
for that C, 100nF works but going by pin spacing must be less than that.

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Diverse Devices, Southampton, England
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