Hello all, I am working a=E7on a 250W SMPS from a PC. The primary part
of the circuit work fine ( or so it seems) but the out put from the
secondary is pulsating. I caonnect a small device i made out of 2 small
light bulbs (one 5V the other 12V,I use this to quickly check for right
voltage output)and i find is pulsating, like on off on off. Can anyone
tell me why can this be? I tought of capacitors but they all seem fine.
I dont have any equipment to check caps, I used a DMM. Any ideas?

Thanks,
Gary.

"onyxx" writes:

Hello all, I am working açon a 250W SMPS from a PC. The primary part
of the circuit work fine ( or so it seems) but the out put from the
secondary is pulsating. I caonnect a small device i made out of 2 small
light bulbs (one 5V the other 12V,I use this to quickly check for right
voltage output)and i find is pulsating, like on off on off. Can anyone
tell me why can this be? I tought of capacitors but they all seem fine.
I dont have any equipment to check caps, I used a DMM. Any ideas?

How much of a load are you lamps? You may need a couple amps on at least
the +5 VDC line for stability.

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On 16 Sep 2005 09:42:29 -0700, "onyxx" wrote:

Hello all, I am working açon a 250W SMPS from a PC. The primary part
of the circuit work fine ( or so it seems) but the out put from the
secondary is pulsating. I caonnect a small device i made out of 2 small
light bulbs (one 5V the other 12V,I use this to quickly check for right
voltage output)and i find is pulsating, like on off on off. Can anyone
tell me why can this be? I tought of capacitors but they all seem fine.
I dont have any equipment to check caps, I used a DMM. Any ideas?

Thanks,
Gary.

Does it do this when connected to the motherboard? It actually sounds
like something is unhappy on the primary side...

Tom

Is the supply current limiting? It sounds like its trying to start up,
and then shutting itself down.
If it is, then yes, it does sound like a control side issue. Closely
inspect the pcb and components, using a jewelers eyeglass (95% of
faults can be found, by careful inspection. To check that a transistor
hasnt died, by desoldering one of its legs and measuring it. Also
check for dry joints.
Good luck.