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switching power supply 24 v - blows fuse

I have a small power supply (that would be expensive to completely replace) which is faulty (blows its own fuse).

I understand that the high voltage (primary) part of the circuit is likely to contain the faulty component and that the transforms/coils are unlikely to be responsible.

That leaves the diodes - 4 in the bridge rectifier part and one other all in the primary part of the circuit.

Any other likely causes of this power supply failure? There are no obviously blown components other than the fuse.

Many thanks, Roy

Reply to
Roy Thomas
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Suspect the switching transistor. If this Q is shorted from C to E it will immediately blow the fuse. It's a common failure in SMPS also.

Good luck, Leo

Roy Thomas wrote:

Reply to
Leo Meyer

Don't forget the electrolytics

Reply to
David C. Partridge

See the SMPS repair guide at the site below.

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Reply to
Sam Goldwasser

Probably the switching transistor, though failure of this is usually caused by another problem like shorted output, shorted secondary rectifier or high ESR electrolyics.

If the switching transistor has failed, I'd recommend replacing the electrolytics as a matter of course,*before* powering on with the new transistor. They are under considerable stress and are the No.1 most common problem in switching supplies. If they are marginal, chances are the new transistor will have a short life.

Dave

Reply to
Dave D

Possibly, you have a shorted MOV (metallic oxidide varistor), it's usually black, but could be green, & it's right across the 120 volt A.C. input. Also, rarely, you could have a bad line choke. Sky.

Reply to
Skype_man

In addition to other suggestions check the bridge rectifier to make sure no diodes in it are short circuit, - great fuse blower although less likely than switching transistor.

Reply to
Ross Herbert

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