Wii Power Adapter... for fun :)

[DanFen]

So I'm trying to learn my way through fixing electronics by practice.

This power adapter was given to me by my friend, instead of throwing away, because in reality you can get a replacement for €15.

The fault is: no power output
My findings: easy... at least 3 blown SMD resistors. At least that's what I can visually see.
Root cause: unknown

I'm going to post some photos of the PCB. The main goal of this post is to simply understand what could have caused them to blow up.

My way of thinking is this: as far as I know resistors don't blow on their own, and blowing up means that a large amount of voltage was sent to them, right?

[stj]

check the mosfet that has the temperature sensor leaning against it.
it's probably shorted and blown the resistors

[DanFen]

OK, I guess I have to take that out then
What makes you think it's the mosfet when there's other resistors closer to it that are not affected?

Originally Posted by stj

check the mosfet that has the temperature sensor leaning against it.
it's probably shorted and blown the resistors

[stj]

because the switching mosfet that drives the transformer is the most common failure in psu's.
so it's always the first place to check

[R_J]

R2 is acting like a fuse for the circuit, it is between the transformer primary and the main DC supply.
R3 (and the one next to it) are between the source pin of the mosfet and hot ground of the primary circuit.
When the mosfet shorts it will blow these resistors. When the mosfet does short it may also damage the mosfet gate circuit including the drive ic.

[DanFen]

Originally Posted by stj

because the switching mosfet that drives the transformer is the most common failure in psu's.
so it's always the first place to check

Originally Posted by R_J

R2 is acting like a fuse for the circuit, it is between the transformer primary and the main DC supply.
R3 (and the one next to it) are between the source pin of the mosfet and hot ground of the primary circuit.
When the mosfet shorts it will blow these resistors. When the mosfet does short it may also damage the mosfet gate circuit including the drive ic.

Amazing explanation! In this case I'll go ahead and remove that mosfet, try to figure out which pins are S G D and come back with info. So far I've always had mixed results testing 3 legged mosfets, hope it's better this time

EDIT: Mosfets are like switches right? So, considering that this mosfet is right at the beginning of the circuit, is the main purpose that of switching on when the correct voltage is present?

[R_J]

The drive ic seems to be a IW1691 The mosfet is switched at around 130kHz It is not acting like a simple on/off switch.
It takes the raw Dc from the main filter cap and switches that voltage at 130kHz across the primary of the transformer, this then (basically) produces the lower voltage on the secondary which is the adaptors output

[DanFen]

I've moved the mosfet out of the circuit to test, and below is how it was tested (just because I always get confused on how to properly test them).

This mosfet is KF2N60I 224.

I think this is the one.

In diode mode (testing the Drain & Source):
Forward testing = 179
Reverse testing = 396

At this stage I think we already have a failed result right? Because a diode should only return a reading one way.

[R_J]

Yes the mosfet is bad, it should check open circuit drain to source. I do suspect the ic will be bad as well, When the mosfet shorts and the source resistors (R3) go open, full 300vdc is applied to the CS pin of the ic via R15.

[DanFen]

This new mustimeter I am using is not showing OL, but maybe I'm doing something wrong. I got it for cheap from a hardware store since my Uni-T died. The Uni-T also had auto-range, so it was easier for someone like me. I'll probably create a thread for the Uni-T, maybe it is fixable

In this case I think I'm calling it quits. You helped me understanding a few things that were not clear before, so the goal is reached. I have plenty of other devices in my box that I can practice on anyway

Thanks to you @R_J and @stj for sharing your valuable knowledge.

[stj]

which uni-t?

[DanFen]

UT139C... it returns an ErrE and turns off

Originally Posted by stj

which uni-t?

[stj]

i think thats the eeprom corrupt or a bad connection to it

[DanFen]

Seems like it. I'll disassemble it and do a visual inspection first

Originally Posted by stj

i think thats the eeprom corrupt or a bad connection to it

[momaka]

Originally Posted by DanFen

In this case I think I'm calling it quits. You helped me understanding a few things that were not clear before, so the goal is reached. I have plenty of other devices in my box that I can practice on anyway

That's a little early, IMO.
Yes, there is a *chance* the main IC may be blown... but there's also a *chance* it may not be blown. So long as the MOSFET Source resistor (that white rectangular box glued to the front of the MOSFET) is not blown open, the main IC may have survived. If it is blown, the IC could still survive... but just less likely.

At the very least, try replacing the MOSFET. Exact same part would be nice, but not necessary. So something more common like an IRFBC20 / IRFBC30 / 2SK2624 (to name a few parts) could work at least for a test. R2 can be replaced with a jumper wire... for now . If the MOSFET Source resistor is blown, again try to replace that with something similar. Again, you don't need to match the part just for a brief test, so often times even 2x or 3x higher the resistance may do the job (but if you can, try to get something closer to the original value). Then, check the rest of the parts on the primary side (i.e. check any resistors for open-circuit and any diodes for a short-circuit). Once that is complete, use the series incandescent bulb trick, as shown here:
https://www.badcaps.net/forum/showpo...4&postcount=70

Since this is a smaller power adapter, a 40W *incandescent* bulb should suffice. Plug in the power supply to the wall through the series incandescent bulb circuit shown above, and see what happens. If the adapter is repaired successfully, you should see proper voltage on its output and the series incandescent bulb will not light up. If the bulb does light up and stays lit for more than a second or two, there are more faults in the adapter. At that point, it may be worth to try and replace the IC on the primary side... thought the problem could still be caused from other components going bad.