Electronics > Repair

Repairing Burned-up Switched Mode Transformer

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rossmoffett:
I'm in the process of repairing a controller for an exotic piece of lab equipment (turbomolecular pump) and I've narrowed down the problem to a 12VDC SMPS transformer.  After all of the silicon and capacitors tested good, I cranked up the supply slowly using a 100W rheostat.  That transformer which had a fan mounted conspicuously above it started letting out its magic smoke.

Is it worth trying to re-wind it?  Replacing the power supply board isn't really an option.  I really doubt the transformer is available (and if it were, wouldn't know how to spec it out).  This is a very limited edition run of Japanese manufacture, circa 1991. 

If I can't re-wind it, the next best thing from my perspective is:

* Reverse Engineer the power circuits
* Remove the busted transformer
* Use external 12VDC / 5VDC sources as needed to replace the burned-out section
Any comments on re-winding a small burned up SMPS transformer?  Thoughts on the above?

Harvs:
Assuming it's an off-line transformer there's a few things you need to know in order to get the isolation correct.

Chances are the easiest (and probably not very expensive) option is to look up a transformer winding company in your local area and get a quote on re-winding it for you.

BiOzZ:
a 12v and 5v switching power supply is not remotely rare and you can get them cheap off ebay (like this 4A one http://www.ebay.com/itm/Double-Output-DC12V-1A-and-DC5V-4A-Universal-Regulated-Switching-Power-Supply-/111153167634?pt=LH_DefaultDomain_0&hash=item19e13ebd12 )

but i have rewound SMPS transformers before ... you simply need to desolder the leads, place some wire on the top and bottom part of the Ecore and heat it up slowly in an oven and pull it apart to break the epoxy and rewind it with proper tape and proper mag wire than glue it back together

many problems can come from this like having it supply too much or too little voltage!

BiOzZ:
also chances are who ever made the company did not make the power supply so if you can find any marks on the supply PCB (manufacturer, numbers etc)  you might find out that that was a common SMPS for the time and get a replacement! especially if its lab gear i dont think anyone would take the time to make a separate power supply, run it, test it exc when they can just buy a common one on the cheap and if there only making like 100 of them the cost of making one alone would be too much (i inturn for a place where we make SMPSs for other companies and do our own testing and getting it too pass FCC and UL standards)

you can also find an equivalent transformer probably somewhere on the internet unless they wound it them selves with some strange specs and id say thats probably not the case!

flolic:
Transformer is shorted anyway. Nothing cost you to try to rewind it.
That should not be too big problem, if you can separate ferrite core...

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