Schematic needed for XYS-300V-12 power supply

[berniedd]

It's a chinese made generic power supply for a CCTV system. The thing has some burned out components whose markings are no longer readable. S-400-R13 is a label on the chassis housing. On the board itself, I see the characters S-400-R13 and D201103. A new psu has been fitted to the CCTV system, but I'd like to bring this one back to life. Any help would be appreciated.

[selldoor]

Re: Schematic needed for XYS-300V-12 power supply

If you can post good clear pictures of the board - back and front - maybe if ts generic
someone can suggest replacement parts - have you tried cleaning with IPA

[berniedd]

Re: Schematic needed for XYS-300V-12 power supply

Here you go. Close up shows the 4 burned components whose marks have been removed by the heat. The underside shows nothing unusual, no burn marks and there are no components soldered there.

[stj]

Re: Schematic needed for XYS-300V-12 power supply

pictures of the other side please.

[berniedd]

Re: Schematic needed for XYS-300V-12 power supply

Ok, here it is. For reference, I just flipped the board upside down away from me from the original position as seen above.

The burned parts are C26, C27, R44, R45. A cursory multitester sweep of the boars parts shows that R7 is open, Q2 (NPN power transistor) D13009K is shorted. The main 8ampere AC fuse is open/burned out.

[stj]

Re: Schematic needed for XYS-300V-12 power supply

did you change the fuse?
because someone did.

there are lots of cracked solder joints too - pretty common on old chinese stuff like this.
it's lead-free solder soldered at the wrong temperature.
and it uses water-soluable flux, but they dont wash it off properly.
you will find the solder hard to melt - you need to use a pump to remove it wherever you solder and then use fresh solder after.

presuming we can find the problem that burned those parts!

[berniedd]

Re: Schematic needed for XYS-300V-12 power supply

Yeah, a handyman replaced the fuse days before it was brought to me. Of course the new fuse also blew.

[budm]

Re: Schematic needed for XYS-300V-12 power supply

Those two resistors and the two caps are the RC Snubber network for those two output rectifier diodes siting on the top egde of the board. The Ceramic caps when they failed, they failed as shorted circuit, they should be rated in 500~1KV range.
For example:
http://electronics.stackexchange.com...ctifer-circuit

The snubbers can be cutout for now just for testing, the RC value will have to be calculated.

BTW, beside bad solder joints, did you check other components for short, such as the those two diodes on the output, the bridge on the primary side, the two MOSFET/TRANSISTORS sitting on the right edge of the board?

[berniedd]

Re: Schematic needed for XYS-300V-12 power supply

Thanks, budm. I haven't gone through the entire board yet, but the power schottky diodes are fine. Of the power transistors Q1 and Q2 (both D13009 NPN transistors) at the right edge of the board, both are shorted. Q2's base resistor R7 is open.

The links are helpful, but the calculations will have to wait till I can take stock of the inductances and evaluate the other board components. Thanks for the info and links. I'm sure many readers will benefit from reading them.