Electronics > Repair
Please help power supply dead 110V to 24vdc 5vdc
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administr4tor:
hello,
this printer power supply is dead,I cant figure out with my limited knowledge that why the lower output part of circuit is not getting any DCV. I have measured voltages across transformer and I found 24v but nothing on the other side of transformer, please have a look at pictures, any help is kindly appreciated. thanks.










Thank you
techie1234:
Transformers don't pass DC from one side to the other - only AC.  Are you measuring AC on both sides of the transformer?
ArthurDent:
That is a switching mode power supply (SMPS) and the connections on the primary side of the transformer could have line voltage on them as well as 160VDC to 400VDC (read the voltage rating on the big capacitor) If you don't know what you're doing, poking around can be very dangerous.
TheMG:
Check the fuse. If fuse is ok, start checking capacitors with a capacitance/ESR meter (most do not need to be taken out of circuit to measure).

Most common cause of a no-output condition on a SMPS if the fuse is intact is one or more bad capacitors especially the smaller ones on the primary side.

Much of the troubleshooting on these things can usually be done without ever applying power, as most SMPS faults are either something shorted (resulting in blown fuse and other components sometimes releasing the magic smoke) and bad capacitors.
Miti:
Be very careful when repairing a SMPS if you don't know (exactly) what you're doing, you may get hurt badly!

That being said, what's the controller chip U1? Don't measure across the transformer windings with a multimeter, it doesn't make any sense, and definitely don't use the oscilloscope in the primary side.
How old is the power supply? The first thing I would check, beside the fuse, would be the three capacitors on the primary side, above the transformer in the second picture. In particular, the one on the supply pin of the controller.
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