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

Its become one of those back-burner jobs.
SMPS on a Yamaha SPX 90.
Its now come to the stage of using a variac and 240V/240V isolation
transformer to scope the mains side oscillator. These diodes are about the
only items left that could be causing the problem, one LV error amp side ,
problem scenario to check first.
Its only 6 to 10W load and putting 2 small transformers in there instread ,
a few bridges and a 5V regulator would have easily solvered the problem - in
hindsight, ditch the SMPS.
SMPS starts up at very short mark space and changes frequency and mark space
but goes over the required steady state into full drive of 60W or so and
heating up the chopper.
Large Ds D2,3,9
small ones D4,5,13
I very much doubt they are faulty as they all cold check the same basic
diode test.

Got another SMPS, for a Uher amp from 1981, going this week but not this
Yamaha one

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