Repairing Extech 382260

[rush2112]

Hello! I recently became the owner of an Extech 382260 variable power supply. I got this while picking up something completely unrelated from a yard sale. The previous owner had been using this for prototyping and something fried on him. As I am also prototyping electronics, I picked it up in hopes of fixing it.

Upon opening up the case I immediately noticed a blackened splotch, not unlike something from Looney Toons. It looks like this was caused by a particularly unhappy resistor. Next to the black splotch is an "R25" which looks to be the resistor that blew and there is a damaged R26, R27, R28 and D9 that look like they should probably be replaced as well as the voltage regulator. I've included a picture showing the unit and the damage:







I have tried to find information on the wiring diagram for this particular unit, but have had no luck. What I am hoping for is that someone might have this unit, and could open the case and take a look at the components that I listed above, and give me some information on them. For example...what is the resistor value for R25? Any information on the voltage regulator (lettering on mine is burnt off)?



Thank you in advance for any information you might have!
-Josiah

[wraper]

Voltage regulator model? Maybe you mean burned MOSFET? R25 likely to be <= 1 ohm if it is connected to the source of that mosfet. UC3843B and all between it and mosfet gate likely is dead as well. If R27 is parallel to the diode and is going to the gate it is something like 47-100 ohm. Diode certainly also is dead.

[tautech]

As wraper has alluded to, it looks like a SMPS to me.
Get the 3843 datasheet and see if you can find a typical application circuit for it, you may find they match perfectly and have the component values you seek.

[Wytnucls]

Manson Rev. 5 PCB
Manson SSP7080 http://www.manson.com.hk/getfile/index/action/product/name/524bb4c50e335.pdf

Regulator is K3565 (1N) (N channel MOSFET).
R25 1k Ohm
R26 100 Ohm
R27 22 Ohm
R28 <1 Ohm Blue/Grey/Silver/Gold/Black
D9 1N4148 http://www.nxp.com/documents/data_sheet/1N4148_1N4448.pdf

[wraper]

If somebody don't know, K3565 is 2SK3565 from Toshiba

[rush2112]

You guys are awesome. I really appreciate the photos Wytnucls, and the time you took to open your unit up.

I'll be picking these parts up soon and hopefully I can bring this sucker back to life!

[Wytnucls]

My pleasure and good luck with the fix. Don't forget the 'After' pictures.

[squeakbat]

I know this is an old thread, but my unit just failed in exactly the same fashion (around the pwm-mosfet area), rather spectacularly with three loud pops and flashes.  I was in the same room but looking the other way.  It was sitting quietly in a corner driving an LED strip, not even close to full power.  I'm a little disappointed with this thing, but will try to repair it since all the information is right here.  Thanks guy!

By the way, if the original poster is listening, your STmicro UC3243B looks cracked, as is mine.  Did you replace that as well?