A perfectly non-functional 5V 5A AC/DC from China

[ckrtech]

I have a DVDO Scaler (iScan HD) from Anchor Bay that asks for 6V 5A DC input. The power supply that was provided with it (secondhand) is... err... was a generic, made in China, 5V 5A AC/DC converter.

It has been awhile since I had last powered it up (and it hasn't been plugged in during this time). Upon plugging it in today, I got a rather abrupt, metallic "pop" from inside, and the LED never lit again.

So I decided to crack it open and take a look.

What blew? The X-cap? That is my best guess - based on... smell.

Should I be using this? No.
Have I been? Yes.
Do I want to spend money to buy a legit replacement? Not really.

Arg. Haha. Photos for your amusement and comments.

[sam_sam_sam]

Re: A perfectly non-functional 5V 5A AC/DC from China

Look at the iC chips with a magnifying glass very closely for burn mark or burn marks on the pins next to body of the chip and look at the bottom of each cap for pop bottoms or signs of leaking and just look the board very closely for anything that looks like it has arcs marks

One time I had a board that would not turn ON it took me awhile to find the burn mark on the IC chip pin on the body of it

I hope this helps

[budm]

Re: A perfectly non-functional 5V 5A AC/DC from China

Do you see any burnt or pop component? I cannot tell from the pictures.

[ckrtech]

Re: A perfectly non-functional 5V 5A AC/DC from China

Apologies for the focus. Should have used an index card or something to help.

I couldn't really find anything that was obviously burned aside from a rather tinged side of the X2 (?) cap?

I don't know how to properly test it, but I can say:

1: I assume it blew
2: 0 ohm when metering the two leads = see #1?

Terrible photos show a somewhat gently mangled bottom of the box and a bad solder joint just underneath.

[budm]

Re: A perfectly non-functional 5V 5A AC/DC from China

Bad solder joint on that one leg.
Remove it and test the resistance again on that cap, it should have caused the main AC fuse to blow if is shorted out since it will be connected between Line and Neutral after the main fuse.
We need straight shot pictures of the whole top and bottom side of the board.

[Per Hansson]

Re: A perfectly non-functional 5V 5A AC/DC from China

...And after taking that cap out of the board also measure the now empty spot on the PCB again.
If you still have a short the main suspect is the bridge rectifier (four diodes in this case?)
And after that the SMPS controller UC3843BN

[ckrtech]

Re: A perfectly non-functional 5V 5A AC/DC from China

I'll try to get some better photos of the PSU top and bottom within the next couple of days as well as get the glue off the component and extract it.

[ckrtech]

Re: A perfectly non-functional 5V 5A AC/DC from China

No continuity across removed cap. Measuring the two PCB points after extraction, I get like 700kohm (increasing).

I bent a small cap near the output side for the photo, and the tension basically lifted a pad for one leg.

[budm]

Re: A perfectly non-functional 5V 5A AC/DC from China

Well something is not right since you were reading 0 Ohms before and that Xcap is connected between Line and Neutral after the LINE filter.
Are you sure that the 4 rectifier diodes are OK, the MOSFET mounted on the heatsink is OK?

[ckrtech]

Re: A perfectly non-functional 5V 5A AC/DC from China

They seem OK. .593 on the diodes. I get a reading when proving each leg combo of the MOSFET.

It is possible that the bad solder joint basically prevented me from accurately getting a reading with the capacitor in circuit since it was detached from the board (more or less) - so measuring resistance with it in circuit was never really an "in circuit" measurement.

[budm]

Re: A perfectly non-functional 5V 5A AC/DC from China

Cap will show infinite resistance unless has bad leakage resistance or shorted out, that cap is not needed for the circuit to function, so what ever shorted out is no longer there since you have verify that the MOSFET and the diodes are OK.
For you to get 0 Ohms something has shorted, bad solder joint on that cap will not cause the readings of 0 Ohms unless it was measurement error.