Identifying 2 diodes?
 

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

Identifying 2 diodes?
 

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


Are these dead? Do you have a curve tracer?

Michael

Identifying 2 diodes?
 

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

Identifying 2 diodes?
 

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

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Identifying 2 diodes?
 

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.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/