Switching supply expertise?

From: ghldbrd_at_ccp.com <(ghldbrd_at_ccp.com)>
Date: Sun May 30 12:16:48 2004

SMPS are always a pain to troubleshoot, and I've always opted to find a
replacement. In this case that isn't probably feasible so ---

I'd buckshot the components in the switch driver, such as the IC. Sounds
like the traansistor/FET isn't getting drive, or it is being biased hard
on. Do you have a bad rectifier on one of the outputs? Escessive load?

If all else fails, maybe you can find another PS that will fit into the
box, with the same voltage outputs/currrent ratings.

Gary Hildebrand
St. Joseph, MO

> Hi,
>
> Rescued an Apple clone from the trash yesterday (Ci Base48) - appears to
> be
> all there, but power supply is dead. I've had a bit of experience with
> small
> DC transformerless switchers, but not with mains power, transformer based
> switchers like this.
 <snip>
> - Power transistor does not appear shorted - Removed from circuit and
> using
> a diode test function, it shows two normal semiconductor junctions.
>
>
> Can anyone offer suggestions on where to look next? Are there any common
> failure
> modes of this type of power supply design?
>
> Regards,
> Dave
Received on Sun May 30 2004 - 12:16:48 BST