Troubleshooting AC/DC circuit board

[soyuppy]

Re: Troubleshooting AC/DC circuit board

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

Thanks for the info. Yes, there's black heatsink tube right next to the main entrance. And removing the heatsink show indeed a fuse. It's pretty small and hard to tell that's its short...but I'm pretty sure it's short.

But I'm more interest in how to remove/replace this fuse. From the look of it, I should be able just remove the fuse leaving the lead join on the board. But seems like the top cap are glued into the fuse. Try to wiggle for movement, but doesn't budge.
Do I have to remove the entire housing from the board as well?

[budm]

Re: Troubleshooting AC/DC circuit board

Fuse is a short circuit device, so just measure it with Ohm meter (no power applied), it should show as shorts, same resistance as when you touch your meter probes together.

[soyuppy]

Re: Troubleshooting AC/DC circuit board

Fuse is a short circuit device, so just measure it with Ohm meter (no power applied), it should show as shorts, same resistance as when you touch your meter probes together.

yep...did that...and yes, it's shorts.

[budm]

Re: Troubleshooting AC/DC circuit board

yep...did that...and yes, it's shorts.

So the fuse is fine then.

[soyuppy]

Re: Troubleshooting AC/DC circuit board

So the fuse is fine then.

May be I'm confused on what shorts.
But fused is tested on Ohm reading. It shows open(1) on meter. So fused is blown. Need to be replaced.

[vinceroger69]

Re: Troubleshooting AC/DC circuit board

what does you meter show when you touch both leads together?

[soyuppy]

Re: Troubleshooting AC/DC circuit board

what does you meter show when you touch both leads together?

when red lead touch black lead, show zero.
When red lead touch top of fuse and black lead touch bottom of fuse, show 1.

[ben7]

Re: Troubleshooting AC/DC circuit board

when red lead touch black lead, show zero.
When red lead touch top of fuse and black lead touch bottom of fuse, show 1.

So, 1 means it is reading an open-circuit?

P.S., Would be helpful if you would just say that it measures open-circuit, because saying that it shows "1" is confusing.

Before you replace the fuse and try to power it on again, you should check the AC input rectifier bridge to see if it is still OK. And check the main switching transistor (in this case, it is built-in to the switching IC, but it still should be testable) for a short as well.

And, also, next time you try to power it on again, put a 40W incandescent lightbulb in series with the AC input. This will limit the current, and can help prevent things from frying again, if there is still a problem in the circuit (or your probe slips and shorts something out, etc...).

-Ben

[soyuppy]

Re: Troubleshooting AC/DC circuit board

Back with updates.
Got all the caps replaces with Panasonic FR series. Match each new cap with the same spec as old one.

But still not getting any power output on both lead.

Any other suggestion where to trouble shoot.

I've been reading a lot on switch power circuit. Most point out that sometime noise would generated from rectifier.

But it's not the case here. The PSU is dead silent.

[budm]

Re: Troubleshooting AC/DC circuit board

So did you also replace the fuse?

[soyuppy]

Re: Troubleshooting AC/DC circuit board

no, I have 3 boards that have the same problem. Right now just focusing on getting one board working. So I have all the caps replace on this one board that has good fuse.

[soyuppy]

Re: Troubleshooting AC/DC circuit board

pics with new caps

[budm]

Re: Troubleshooting AC/DC circuit board

So you do have 160VDC between the two legs of the main filter cap?
And you also replace that small lytics start-up/running cap in the primary side?

[soyuppy]

Re: Troubleshooting AC/DC circuit board

yes 160VDC is measured but only the radial caps was replace didn't know about the other that need to be replaced. which one are they? do u think they are bad as well?

[stj]

Re: Troubleshooting AC/DC circuit board

check for cracked soldering like in the circle.

[soyuppy]

Re: Troubleshooting AC/DC circuit board

i'm a bit in experience when it comes to visual inspection. But I just tried resolder the crack as shown in the red circle. Doesn't do it...still same problem.

Which component is the bridge rectifier? There are several IC chips, can any of these be the culprit? Is there way to test for these?

[soyuppy]

Re: Troubleshooting AC/DC circuit board

There's a chip on board next to BD1. I assume this is the Bridge Rectifier?
Testing this with ohm meter setting at 200ohm. Tried to test all for legs and couldn't get any reading out it.

Could this be the culprit?