How to troubleshoot dead power brick

[mmartell]

I have an adjustable power supply having a selectable voltage from 15v to 24v. It was sold as a universal soundbar power supply.

It has been outdoors in the elements powering a set of outdoor bluetooth rock speakers until recently when it stopped working. (ya ya I know...)

I opened it and it looks like there was some liquid ingress but I can't find any shorted silicon and the fuse is not blown. I measure about 160v dc after the bridge rectifier but nothing at the main cap. I suspect the power ic is not running. Obviously there is no voltage on the secondary either.

How would I go about determining if the power ic has failed or what would be my next thing to look at ?

[CapLeaker]

hmm... I guess you know the drill!

[sam_sam_sam]

hmm... I guess you know the drill!

I second this idea and thought

[mmartell]

I'm not asking for specifics more general theory. The unit has two large heatsinks covering the components only the back surface mount stuff is visible currently.

[CapLeaker]

Probably something is open in the primary. Make sure the secondary isn’t shorted.

[mmartell]

I have about 8.5v on the startup pin of the power ic which should be enough to start it but only 3.7v on the run pin which isn't enough. Maybe high esr on one of the caps in that circuit going to take off the hot side heatsink tomorrow.

[CapLeaker]

But you got nothing nothing at all on the main cap and that’s your problem. You need to see the 160VDC not only on the bridge rectifier, they need to be present at the main filter cap on the primary too.

[mmartell]

But you got nothing nothing at all on the main cap and that's your problem. You need to see the 160VDC not only on the bridge rectifier, they need to be present at the main filter cap on the primary too.

Ya scratch what I said about the main filter cap since when I measured that the mosfet was pulled off the board with the large heatsink... I had 170v on the main filter cap with it reassembled.

But I'm looking at the startup section and there is something looking like a tantalum cap (but bigger?) labelled "RT" any idea what that refers to ?

[mmartell]

Here are some pics the component in question is in the third pic just above the "4" in 400 in the middle of the main filter cap.

[прямо]

Sensor thermistor maybe? does it look like this picture?

Hard to see from your photo because the lighting is inadequate.

[sam_sam_sam]

There seems to be some issue with the right hand side of back side of the board there seems to be a lot of flux residue that needs to be removed and you need to look very closely and carefully and each soldering joint I would highly recommend that you put the soldering iron on each one of those soldering joints where all that flux residue becomes this section of this board the soldering joint look questionable at best

I would recommend using flux remover or the right type of alcohol to remove the the flux off of the board if you decide to board wash method make sure that the board is completely dry before applying power to the board

[CapLeaker]

A lot of oxidized solder, exposed traces etc. Make sure the traces are good. Hard to tell what that component is in the picture… I buess a thermal resistor and it has to be good, since you did get 170V into the main filter cap. Look at the components and traces between the FET and 8pin IC PWM

[petehall347]

do you have frequency on your meter ?

[mmartell]

do you have frequency on your meter ?

Yes

[mmartell]

There seems to be some issue with the right hand side of back side of the board there seems to be a lot of flux residue that needs to be removed and you need to look very closely and carefully and each soldering joint I would highly recommend that you put the soldering iron on each one of those soldering joints where all that flux residue becomes this section of this board the soldering joint look questionable at best

I would recommend using flux remover or the right type of alcohol to remove the the flux off of the board if you decide to board wash method make sure that the board is completely dry before applying power to the board

That is from me removing the heatsink the first time.

The joints are all good.

[mmartell]

A lot of oxidized solder, exposed traces etc. Make sure the traces are good. Hard to tell what that component is in the picture… I buess a thermal resistor and it has to be good, since you did get 170V into the main filter cap. Look at the components and traces between the FET and 8pin IC PWM

I've ohm'd out these traces and they're ok even though they look bad and are exposed.

I will take care of that if I repair it and decide to put it back into service.

And yes it looks like the picture above thanks for confirming it is working.

[CapLeaker]

I've ohm'd out these traces and they're ok even though they look bad and are exposed.

I will take care of that if I repair it and decide to put it back into service.

And yes it looks like the picture above thanks for confirming it is working.

O.k. Now check the two small caps next to the heat sink and that 8 pin IC.

[mmartell]

Already checked the caps with an esr tester and both are under 2 ohms iirc ? How do I test the 8 pin ? Its an OB2269CP

[CapLeaker]

mmartell
Measure the DC voltage on each pin of the OB2269 and note it down. Download the spec sheet and then let's see what gives. Could be very well the PWM is toast and doesn't wanna do anything. And before I foget it… take some 99% IPA or Acetone and Clan of the bottom of the PCB.

[mmartell]

mmartell
Measure the DC voltage on each pin of the OB2269 and note it down. Download the spec sheet and then let's see what gives. Could be very well the PWM is toast and doesn't wanna do anything. And before I foget it… take some 99% IPA or Acetone and Clan of the bottom of the PCB.

Sorry I was just looking at this again and came back to say I was measuring resistance between gate and source of the mosfet at about 32 ohms so I took it out and measured the pads instead and was the same. After removing the power ic those same pads measure 10k.

Does that indicate a problem with the ic or is that expected ? If it's normal I'll reassemble and take the voltage readings on the pins of the ic. Thanks.