Help diagnosing PWO1025 SMPS

[snoptel]

Wondering if anyone can offer some insight into solving the problem with this SMPS.

Model is - PWO1025

Manufacturer - Power-Win Technology Corp.

So, it was working unit I accidentally shorted one voltage rail to ground while troubleshooting one of the logic boards power by this PS.

I replaced a blown fuse and a fried bi-polar transistor and now I have 33VDC, 12VDC but 5VDC and 3,3VDC are missing.

A schematic would be nice, but the manufacturer doesn´t make them available - I asked.

Anyone know what I could check, I really don´t want to reverse engineer the thing.

FYI - Some components have been removed in the last picture, that's not the source of the problem

Thanks

[R_J]

Is the 5v and 3.3 v supplied by the same transformer as the 33v and 12v? Sometimes there are low value resistors between the transformer and the supply diode, it may be open.
You could provide a high quality, in focus picture of the trace side of the power supply and we may be able to trace the problem

[stj]

do those voltages get switched by the blue relay?

[snoptel]

Thanks for the reply guys.
I´ve uploaded some more pictures.

R J - I traced the 5V supply from the end of the board all the way to the IC circled in blue. Seems like that's where it comes from. As for the 3.3VDC, I have no idea - it isn't even labeled on the board´s output pins.

stj - I haven´t followed the circuit leading up to or from the blue relay.

Keep´em coming

[R_J]

The 12v is not supplied by this board, P160 connects to P164 only. What makes you think there is a 3.3 volts on this board?
The +5 volts is derived from the voltage (10~40v) which will be on the 3 amp fuse, U2 is the 5 volt controller which drives the base of Q2, (10~40v) is supplied to the emitter and the +5volts will be on the collector, which finds its way through the coil L9, through R52/R59 through L13? to the plug. The +5v is monitored (via pin1 of u2) and may not be there unless there is a load on the 5 volt line.

I replaced a blown fuse and a fried bi-polar transistor

Which transistor was blown? and was it shorted ? if it was Q2 that was blown, U2 may also be damaged.

[snoptel]

Hmm, not sure. The board powers a Bernina embroidery machine. On this board there are only two cables connected, one on pins 164 and the other on the yellow pins labeled with 33v, GND, and 5v.
Prior to my bad luck of shorting 5V to GND, I had all four voltages on a second control board powered from this PS, connected via de aforementioned two cables.

I´m starting to think that the 3.3VDC come from the control board powered from this board.

I have 33VDC and 12VDC from this board, if I can only figure out what's faulty with the 5VDC rail I think the 3.3VDC will also be resolved.

[R_J]

There is a diode near C35 and the yellow plug, this could be a zener diode and may be shorted or damaged killing the 5 volts.

[snoptel]

I actually measured that zener in place and reads shorted on the multi meter in diode mode, however it was in place.
If I get a moment today I´ll remove it and check.

I will revert back ASAP.

[snoptel]

Originally Posted by R_J

The 12v is not supplied by this board, P160 connects to P164 only. What makes you think there is a 3.3 volts on this board?
The +5 volts is derived from the voltage (10~40v) which will be on the 3 amp fuse, U2 is the 5 volt controller which drives the base of Q2, (10~40v) is supplied to the emitter and the +5volts will be on the collector, which finds its way through the coil L9, through R52/R59 through L13? to the plug. The +5v is monitored (via pin1 of u2) and may not be there unless there is a load on the 5 volt line.
Which transistor was blown? and was it shorted ? if it was Q2 that was blown, U2 may also be damaged.

Sorry, I didn´t see this reply.
Yes, the bi-polar transistor Q2 and the fuse directly above it were blown. Once I replaced the fuse and transistor I got 33 and 12VDC connected to load.
I did follow the 5v rail and found my way to U2 and to the bi-polar Q2 and you are right on what you say regarding the circuitry.
I suspect U2 may be damaged.

Once I check the zener, I may just order another U2 and replace it..

[snoptel]

Ok, checked the zener, reading is 0v on both forward and reverse bias.
Monday I´ll swap it with a new one and go from there.
Thanks for the help!!

[R_J]

Originally Posted by snoptel

Ok, checked the zener, reading is 0v on both forward and reverse bias.
Monday I´ll swap it with a new one and go from there.
Thanks for the help!!

I take it you are using diode test (0v) then it is indeed shorted, remove it and check it's resistance out of circuit to be sure it is the diode that is shorted and not something else on the 5v line.

[snoptel]

Yes, diode test. The reading of 0v is with the zener removed from the circuit.
Resistance value is around 1 ohm both ways, forward\reverse.
Tomorrow I´ll swap it and see.

[R_J]

If the protection zener is shorted, that would definitely kill the 5 volt supply. hopefully that is all that is left that is wrong.

[snoptel]

fingers crossed.

[snoptel]

Hi R J, it's alive!!

Swapped the zener and now all four voltages are present.

Thank you and everyone else for the help.
SOLVED!!

[sam_sam_sam]

One more item that did not end up in the landfill
Good work repairing it

[UglyBetty]

Great to hear you had a positive outcome. I need to learn more about zener diodes.