Dps-240fb

[rtstorm]

Re: Dps-240fb

I think the small transformer is the problem. I check this way voltage and get on primar 40V and secundar 0V.

Is this OK?

[ben7]

Re: Dps-240fb

Likely the meter is getting confused, since the voltage on the primary will be a high frequency signal.

[rtstorm]

Re: Dps-240fb

Ok, i am lost i dont know what to check? All components is ok, but PSU wont start. Could it be problem with litle transistor on small pcb board?

[ben7]

Re: Dps-240fb

What voltage (DC) do you get across pins 1 and 2 of the TNY268?

[rtstorm]

Re: Dps-240fb

i get 0.3V

[ben7]

Re: Dps-240fb

Could you check that diode between the capacitor c9x and the transformer?

[rtstorm]

Re: Dps-240fb

the diode is OK

[rtstorm]

Re: Dps-240fb

I remove the 10 Ohm resistor from the picture and it is faulty. 0 Ohm show on multymeter. i hope this is the main issue.

[ben7]

Re: Dps-240fb

I remove the 10 Ohm resistor from the picture and it is faulty. 0 Ohm show on multymeter. i hope this is the main issue.

Interesting. Yes, it looks like it has burnt. But, 0 ohms? I have never heard of a resistor shorting out - EVER!

[rtstorm]

Re: Dps-240fb

i replace it, and have a run. When i plug into wall socket, strange hi frequency sound comming out PSU, i check stand by V and it was 5V. I try to turn it on with wire (grenn+black) and for a few seconds fan start to spin, and then BANG!!

I turn it off, and see that R8, R9 and R12 resistor is burned.

Is this failure happen because i use 100uF 450V (big cap) instead of 150uF? or something else is wrong.

[ben7]

Re: Dps-240fb

i replace it, and have a run. When i plug into wall socket, strange hi frequency sound comming out PSU, i check stand by V and it was 5V. I try to turn it on with wire (grenn+black) and for a few seconds fan start to spin, and then BANG!!

I turn it off, and see that R8, R9 and R12 resistor is burned.

Is this failure happen because i use 100uF 450V (big cap) instead of 150uF? or something else is wrong.

Did you have all parts soldered in? What about solder bridges?

I highly doubt the capacitor caused the problem.

[rtstorm]

Re: Dps-240fb

yes i solder all part. i dont see any solder bridge. The BANG was very strong. I will try to replace resistors and clean all board. The explosion was in that area near resistors.

[rtstorm]

Re: Dps-240fb

uhh how to find out the value if resistor, they are burned

[ben7]

Re: Dps-240fb

Check Q1, D4, and Q2 again.

In this picture here,
https://www.badcaps.net/forum/attach...9&d=1372797195, there are aome diodes on the bottom left corner of the pcb. Can you test them?

Also, there might be a problem on that daughterboard, so whatever you do, don't fire up the PSU again until we have a good look at it!

Edit: we have pictures in the first page of this thread. And there was discussion about the values of the resistors also.

Edit2: this is why the lightbulb tester is useful, to prevent catastrophic failures like this one...

[rtstorm]

Re: Dps-240fb

Edit2: this is why the lightbulb tester is useful, to prevent catastrophic failures like this one...

the main fuse did not burned, so i dont think that the lightbulb would help.

I will check these component

[ben7]

Re: Dps-240fb

the main fuse did not burned, so i dont think that the lightbulb would help.

BUT, it takes time for it to burn out. In SMPS circuits, usually the fuse isn't fast enough to prevent big failures. It is still included though to break the current flow when there is a sustained short. Or else things could get hot enough to catch fire, etc...

[rtstorm]

Re: Dps-240fb

D2 diode is broken (run on both sides) BYV 26C PH
D1 is OK.
Q1 - i am not sure, i think it is OK no shorted pins.
D4 is OK
Q2 is OK

i found value of resistor.

Ok, i wont turn it on until we check all.

[ben7]

Re: Dps-240fb

D2 diode is broken (run on both sides) BYV 26C PH
D1 is OK.
Q1 - i am not sure, i think it is OK no shorted pins.
D4 is OK
Q2 is OK

i found value of resistor.

Ok, i wont turn it on until we check all.

It's possible that D2 is what was causing the shorting. However, could you get a picture of the bottom side of the PSU in that general area?

[rtstorm]

Re: Dps-240fb

I think D2 was ok before, i canot remember. I order K3473 FET (Q1) i am not sure that it is ok. Tomorrow i will replace burned resistors and diode. I suspect that Q1 is open all the time. I thinkit is N-channel FET and i am not 100% sure how to test it.

[ben7]

Re: Dps-240fb

You sure D2 is ok? Test it by using diode test mode on your multimeter. It should measure something in only one direction. If the reading you get is on both ways, or it is lower than 0.2, then the diode is bad.

Could you try removing and then testing that ceramic capacitor under that coil near D2? See if the capacitor is shorted.