Troubleshooting External Power Supply

[dfbills]

Hi all-

I had a 12v 12.5A external power adapter fail the other night after being powered continuously for 6-8 years. I've replaced a few capacitors in other projects now, so I decided to replace the 6 obvious and large caps on the board, but this didn't fix the problem. I'm getting 0v out of the supply when powered up.

When replacing the caps, I used same spec replacements:

1. 25v 820uF x3
2. 35v 220uF
3. 25v 330uF
4. 420volts 150uF

Any help in further troubleshooting would be greatly appreciated. Pics of the board are attached.


Dave

[CapLeaker]

Re: Troubleshooting External Power Supply

how much DCV are you getting on the big 420V main filter capacitor? be careful measuring this!

[dfbills]

Re: Troubleshooting External Power Supply

Hey CapLeaker- Can you explain how to do this? Possible without removing the big cap again?

[budm]

Re: Troubleshooting External Power Supply

1) To be sfae when making Voltage measurement in the HOT Deadly side is to at least plug the power supply into GFCI OUTLET.
2) Did you already verify that fuse F1 in the hot side is good?
3) If the fuse is good then you can measure the DC Voltage between the tow legs of 150uf 450V cap.

[dfbills]

Re: Troubleshooting External Power Supply

Hey budm-

Thanks for the response. I had looked for a fuse, but I haven't been able to find one. Are you actually seeing an F1 on the board?

[budm]

Re: Troubleshooting External Power Supply

https://www.badcaps.net/forum/attach...6&d=1584125765
It is the red rectangular shape fuse right next to the rectangular yellow cap.

[dfbills]

Re: Troubleshooting External Power Supply

Thanks, yes that T4.0A 250V STA fuse is failing my continuity check. Dare I bridge that fuse to test? ...while I wait for a replacement to come by mail

[dfbills]

Re: Troubleshooting External Power Supply

While I'm setting up another order, any other components I should consider replacing? I strongly suspect that the large cap was the culprit as it had some small leakage on one leg.

[CapLeaker]

Re: Troubleshooting External Power Supply

Check if the bridge rectifier is shorted. Usually the fuse doesn’t blow for no reason.
Caps can look absolutely good and yet test bad. Hard to tell without an ESR tester.

[dfbills]

Re: Troubleshooting External Power Supply

Can you help me locate the bridge rectifier on this board? I'm not seeing the 4 diode configuration, although the LF102 appears to be square..?

(This might be going beyond my ability to repair.)

[petehall347]

Re: Troubleshooting External Power Supply

on your pic of underside of the board rectifier is bottom right . 4 pins .

[dfbills]

Re: Troubleshooting External Power Supply

Square "A" or Rectangle "B"?

[diif]

Re: Troubleshooting External Power Supply

Rectangle B, This video will show you how to test it. https://www.youtube.com/watch?v=dqkT6hF0O3E

[budm]

Re: Troubleshooting External Power Supply

https://www.badcaps.net/forum/attach...9&d=1584303207
Check the resistance between S and D pin of the PFC MOSFET Q601 to see if it shows really low resistance reading or not.

[R_J]

Re: Troubleshooting External Power Supply

If the fet and bridge rectifier check ok, I know If the main cap is bad (as in open) this will blow the main fuse. So it might be that all that is wrong IS the main filter.