Looking for a Diode Module Substitute

DarrenF

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Working on a switcher which has had the -5V line shorted.
There's a diode module (3-leg) device between the output choke and the transformer; it's shorted. Looking for a substitute.

Markings:
"PHOTRON"
"PSR16C40PT"

Can't find any thing from NTE, Mouser, MCM, Digikey...
 
Got a pic of it?

That sounds awful big to be in the -5v path... Most -5v power supplies are around .5 to 1.0 amps of current and are done with small, separate high speed switching diodes and not a big 3 legged one.

Also, are you sure it is shorted? High speed diodes can read low in one direction and pretty dang low in the other. Also, the 2 outside legs will be hooked to the transformer so they will appear to be shorted in circuit. To truly get a good reading you should take it out of the circuit.

RJ
 
Got a pic of it?

That sounds awful big to be in the -5v path... Most -5v power supplies are around .5 to 1.0 amps of current and are done with small, separate high speed switching diodes and not a big 3 legged one.

Also, are you sure it is shorted? High speed diodes can read low in one direction and pretty dang low in the other. Also, the 2 outside legs will be hooked to the transformer so they will appear to be shorted in circuit. To truly get a good reading you should take it out of the circuit.

RJ

Thanks for the reply.

Yes, I have a pic, but I don't think we need it now.

I may have mis-traced the circuit path thru a coil containing several different wires wrapped around a toroidal core. Let me back up, and re-group...

The PS worked fine until I did a bone-headed thing and trusted a pinout I found online without verifying it on the schematic (My fault. Lesson learned.) As a result, the -5V line was shorted directly to ground. When I powered it on, the 5A breaker on the PS tripped... but not after an unhealthy buzzing and a little pop & flash inside the PS. I unplugged the PCB, found the mistake in wiring, and powered on the switcher (alone) again: same result. Something had shorted in it.

So I thought I'd traced the -5 line to the subject component, but I may have been mistaken.
In any case, I took it out of circuit, and it tests as follows:
Forward bias: ~0.3V (both outsides legs to center leg)
Reverse bias: out of range (both to center)
That seems good to me.

Also, I thought I'd be able to use the PS w/o the -5V line with this diode module out of circuit. So I put it back together and... same result: trips its breaker. So my problem must be elsewhere in there. Back to the drawing board...
 
Switchers don't pop breakers or fuses typically over problems in the low voltage side of the supply. Check the high voltage side - particularly the bridge rectifier and the main switching transistor.

If the main switching transistor is bad then you must check each and every resistor and diode in that area of the board too.

RJ
 
Switchers don't pop breakers or fuses typically over problems in the low voltage side of the supply. Check the high voltage side - particularly the bridge rectifier and the main switching transistor.

If the main switching transistor is bad then you must check each and every resistor and diode in that area of the board too.

RJ

Roger that. Will check out that side of it tonight.

Thank you.
 
OK, here's what I found:

-The dual-diode module package thing does appear to be for the +5 line, and does seem to be fine.

-One of the diodes on the secondary side for the -5V output (got the right ones, now...) is shorted. They are marked PR2003.

-On the primary side, both of the main transistors, marked C2335, are short between the base and emitter. One of them has a nice hole burned in it...

-The input bridge rectifier is similarly burned thru, and has shorts between the AC & DC legs.

I really did a number on this guy...

I've got an appropriate bridge for replacement, but I'll need to ID and source some subs for the xistor & ultra-high-speed diodes.
 

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