Troubleshooting AC/DC circuit board

[soyuppy]

Not sure if this is the right forum. It's it relating to AC/DC circuitry. Figure its in the same domain as PSU.

I have fault AC/AC circuit board. 2 different DC voltage are output. One is 3.3V and another is 14.8V.

Upon inspection, nothing looks burned and caps look clean. Doesn't look like there's any faulty component.

Understand typically there's fuse, but can't seem to find the fuse box either. I have confirmed output from the AC housing prior to entry onto the IC is in tact with ~120VAC.

Where would I start to diagnose this board? Is there a way to test if transformer?

[stj]

Re: Troubleshooting AC/DC circuit board

relpace the 47uf startup cap
use something semi-decent like a panasonic FR series.

[budm]

Re: Troubleshooting AC/DC circuit board

OK, you will be making Voltage measurement in the hot deadly side of the circuit so you MUST BE REAL CAREFUL.
We need better straight shot pictures of the whole top side and the bottom side of the board so I can locate the main AC fuse.
Right now we do not know if the SMPS circuit is getting the DCV to run or not, so you should check and see if you have 160VDC on the two legs of the main filter cap (big brown cap laying on the side with yellow tap on it) first. If there is no voltage there then we need to check the main fuse and the bridge rectifier.

[soyuppy]

Re: Troubleshooting AC/DC circuit board

relpace the 47uf startup cap
use something semi-decent like a panasonic FR series.

Forgive me as I very new at this. Can I use a 47uF 50V to replace this 47uF 35V do I have to find the exact 47uF 35V?

[stj]

Re: Troubleshooting AC/DC circuit board

50v is fine.

[soyuppy]

Re: Troubleshooting AC/DC circuit board

more pic of top and bottom as requested

159.99VDC is measure on the capacitor

[budm]

Re: Troubleshooting AC/DC circuit board

OK, so we get to see to top side of the power supply board, I can see at least 3 bad caps with bulging top, I would replace all 4 in the secondary side.

[stj]

Re: Troubleshooting AC/DC circuit board

panasonic FR series preferably, whatever ou use - no 85' temperature junk.

[soyuppy]

Re: Troubleshooting AC/DC circuit board

thanks for the advice. Will look for Pan FR series from either Amazon, DigiKey or Mouser.

Probably will replace all the caps, including one in the primary as suggest by @stj. But in doing so, I will need to remove and reseal the white caulking material as well?

What is this material call?

[budm]

Re: Troubleshooting AC/DC circuit board

You can use hot glue or electronic grade Silicone RTV not typical Silicone RTV which is corrosive.

[soyuppy]

Re: Troubleshooting AC/DC circuit board

Well, I hope it's ok to continue this thread on different topic/question.

I'm trying to remove the cap from the board. My soldering gun can't seem to melt the old solder. But it can melt new rosin-core. Does this mean I need a new gun with more power just to melt the old lead on the board?

[budm]

Re: Troubleshooting AC/DC circuit board

What is the wattage of this soldering iron? Tips size? The trick is to add more solder and flux to the joint first.
What tools do you have for removing the melted solder?
You should practice on scrap board so you will not damage then board you are trying to fix.

[soyuppy]

Re: Troubleshooting AC/DC circuit board

Old gun had over 20 yrs now. Can't tell what wattage anymore because the label is all washed out. Chances are it's not lead free and the board probably use lead free which require more heat/new gun.

I'm also using the wire mesh/braid to remove the solder.

Will look into new soldering gun. Anyone to recommend? Seen Weller on Amazon but they are a bit $$$.

[dj_ricoh]

Re: Troubleshooting AC/DC circuit board

Old gun had over 20 yrs now. Can't tell what wattage anymore because the label is all washed out. Chances are it's not lead free and the board probably use lead free which require more heat/new gun.

I'm also using the wire mesh/braid to remove the solder.

Will look into new soldering gun. Anyone to recommend? Seen Weller on Amazon but they are a bit $$$.

YES! and every time you solder and power up the weller its orgasmic!

it makes you feel like you build a space SHIP!
hahhahaa

[soyuppy]

Re: Troubleshooting AC/DC circuit board

In the process of testing and out the output from various capacitor, spark fly and this happen. See pic

The blow lead belong to the transformer...the big block module sitting in the middle of the board.

Does this mean it's bye bye? Or can I just resolder it? How do I test transformer.

[budm]

Re: Troubleshooting AC/DC circuit board

Clean off the black carbon with IPA first and look at the pin really well, it looks like it has cold solder joint on that transformer pin.

[soyuppy]

Re: Troubleshooting AC/DC circuit board

not sure what to make of this. Appreciate any pointer

[budm]

Re: Troubleshooting AC/DC circuit board

It looks like the trace burnt open. Did that location make contact with other conductor or something while you were probing the board?
But looking closer I can see that the pin has bad solder joint, so you can try fixing that connection and resolder all the pins of the transformer as well.

[soyuppy]

Re: Troubleshooting AC/DC circuit board

I was probing the caps...and then it just sparkle. Wasn't sure what it was...until i see the black charred. I decided to disconnect and kind of don't want to do anything else now

Will re-soldering cover the trace burn out? If I resolder and reconnect, how do I tell/test if transformer still operating? can I read it off volt meter? there's a lot of lead wire onto the board...wasn't sure which wire to tap on the volt meter.

[ben7]

Re: Troubleshooting AC/DC circuit board

I was probing the caps...and then it just sparkle. Wasn't sure what it was...until i see the black charred. I decided to disconnect and kind of don't want to do anything else now

Will re-soldering cover the trace burn out? If I resolder and reconnect, how do I tell/test if transformer still operating? can I read it off volt meter? there's a lot of lead wire onto the board...wasn't sure which wire to tap on the volt meter.

The fuse on the PSU might be blown as well now too. It's covered in some black heat shrink tubing.