KPS305D Bench Power Supply

[abbas101]

When Turns on Its shows approx 4volt and goes to zero. No Current and No voltage at output. Uses TNY277GN My question if any one knows the voltage between drain and source pins, Currently it is like going into loop from 0 to 330Volts. Thanks

[sam_sam_sam]

Re: KPS305D Bench Power Supply

Look for a diode across the output terminals or on a board that might be shorted
This would be the first thing that I would look at

The second thing I would do is replace the TNY277GN these type of devices have a history of going bad for apparent reason

Or the capacitors around the TNY277GN might be the first thing that I would try before replacing the TNY277GN ic chip

[abbas101]

Re: KPS305D Bench Power Supply

Thanks SAM

I checked diodes and all seems ok. I also have doubt on TNY277 but before replacing want to be 100% sure.

[R_J]

Re: KPS305D Bench Power Supply

If the source pin connects directly to hot ground (- of main bridge rectifier) then there is no way that the TNY277GN is dropping the 300v to 0, it's top would have blown off the top. Check the voltage across the man filter capacitors, is it also dropping? if it is staying at 300v, check the components between the main filter and the drain of ic501

[abbas101]

Re: KPS305D Bench Power Supply

R_J I will check and will post results tomorrow. I did the checking last time and AC circuit was ok (at least seems ok)

[stj]

Re: KPS305D Bench Power Supply

i presume this unit doesnt have a stupid PFC circuit?

[abbas101]

Re: KPS305D Bench Power Supply

Hi Guys, trouble shooting is going on in slow motion. I found shortage on smd capacitor c44 and pin 4 and 5 of LM358, Remove the capacitor and checked it but it was not short. Removed LM358 and it seems ok outside the board but still there is short between pad 4 and 5. Is it normal ? please advice