LG Washer/Dryer Power Fail

[momaka]

Re: LG Washer/Dryer Power Fail

The only exception is the 47uF start-up cap that momaka and stj mention. This one reads 40uF 1.2 Ohm which isn't exceptionally bad I don't think, but I will see if I can find a better one.

1.2 Ohms is indeed not bad for a small cap like that. Nevertheless, knowing that this appliance is made by LG, the cap is probably a SamYoung, SamWha, or some other similar Korean brand (or worse - Chinese) that aren't known for their reliability - in which case, it wouldn't be a bad idea to replace it anyways. Same can be said about the rest of the PSU caps, if they are of the same inferior brand, but since this is not the problem here, I agree that you don't need to replace them.

Since you've identified that the issue happens when the dryer fan is running, it may be a good idea to measure its current draws, as redwire and petehall347 suggested. Should be easy to do with a multimeter.

Also, if bad comes to worse, you can always disable/disconnect the washer/dryer power supply's 22V rail and instead wire it to an isolated 20V laptop power adapter. That should provide more than enough current for the fan.

its 6 years old and fine until now .. even if original spec parts are replaced it in theory will do another 6 years .

Not necessarily.
If the dryer fan bearings are starting to go bad indeed (or even not bad but just aged and showing slightly more friction), it's possible for this to make the fan draw more current. And if the washer power supply was marginal or not specced properly to begin with, then a new replacement TOPswitch very likely won't last the same amount of time.

[petehall347]

Re: LG Washer/Dryer Power Fail

its 6 years old and fine until now .. even if original spec parts are replaced it in theory will do another 6 years . only if the other parts will last that long .
i say run the fan off an external supply . add a 1 ohm resistor and voltmeter and calculator or simply an ammeter of an accurate clamp on type if you like .

[redwire]

Re: LG Washer/Dryer Power Fail

The blower fan may have aged and is using more current, and the power suppy is undersized.
I would run the blower from a DC power supply and see if the motor is ok and no lint and crap blocking it, doesn't need oil, brushes OK etc.

The TOP242 is the lowest power part in the family.
You could drop in a higher power part like TOP243 or TOP244 which would (only) run cooler due to the much lower on-resistance.
Have to check if this would work - the transformer current must be the same, the circuit must have the resistor on the X pin. If so, you can drop in a beefier part.

TOP243 which has 1/2 the on-resistance and more output power (25W vs 15W), or TOP244 which has 1/3 the on-resistance (28W vs 15W). Lower on-resistance = less heat. Potentially 1/2 to 1/3 the heat.

[stj]

Re: LG Washer/Dryer Power Fail

check the blower spins o.k.
a friend had to replace one because the bearings had corroded.

[AdrianM]

Re: LG Washer/Dryer Power Fail

Thanks everyone. I ended up prising the board out after running a knife around the edges.



The potting compound is very soft and not too bad to scrape off to get to the component pads. I started with the 330uF input cap but this actually metered-up OK @ 322uF 0.28 Ohm.



I've since exposed all the parts in the PSU area and none of the caps are out of spec. Sure I can re-cap them all but some have lower ESR than the new ones I'd be replacing them with so I think its a red herring. All the bigger O/P filter caps are good low ESR types. The only exception is the 47uF start-up cap that momaka and stj mention. This one reads 40uF 1.2 Ohm which isn't exceptionally bad I don't think, but I will see if I can find a better one.

Notice though that there are some browned areas notably above the SM diode that's rectifying the 22V feed that ultimately powers the dryer fan. The TOPswitch output transformer also has two 12V outs, one of which feeds the logic stuff via a 7805 and another isolated tap that seems to be referenced to the HT for something or other. I think the 16.5V may be for the IGBT driver for the drum motor.

These supplies are all fine when loaded by the washer cycle alone. But as soon as the drying cycle is engaged the 22V supply comes into play and this is what ramps up the heat in the TOPswitch. The dryer fan is by far the biggest load supplied by the regulator. I guess it could be a problem with the fan? It runs OK and, as I said before, if I blow air over the TOPswitch it settles down to a sensible temperature and will run all day like that. I'm mighty puzzled now.

[stj]

Re: LG Washer/Dryer Power Fail

topswitches are fine if the startup cap is good.
if it fails the top can explode.

[CapLeaker]

Re: LG Washer/Dryer Power Fail

As I recall, these TOP242 or similar IC's are known to fail. I'd recap the board and put a new TOP242 and be done with it.
Makes me wonder... I have a 2 year old LG washer (no washer dryer combo) and it looks similar to yours.

[momaka]

Re: LG Washer/Dryer Power Fail

Check the small startup cap and also the output caps of the SMPS. I think those would be the primary suspect in causing the TOPswitch to overheat. In addition to that, maybe add an aluminum ribbed heatsink on top of the TOPswitch with some thermal adhesive (Arctic Cooling has a two-part thermal adhesive suitable for that).

[stj]

Re: LG Washer/Dryer Power Fail

try melting it with white spirit, it works on Honda ECU's

[AdrianM]

We have a 6-yr old LG combo washer dryer model 1480YDS that has started to cut out part way through the drying cycle. This has now become a highly repeatable failure giving me a chance to diagnose the problem. On restarting the machine (after an imposed wait of a minute or two) the display would show PF (power fail error) indicating an unexpected removal of power part-way through a programme.



Searching around the internet this fault seems to be fairly common to a wide range of similar LG washer dryers and because the only solution people were finding was to replace the entire control board for around £130, I decided to work out what sub component was failing.

I wondered initially if it might me a glitchy relay or something else relating to the drying phase causing the microcontroller to crash out because the machine would happily do a full wash lasting over an hour, but would always stop after 5 minutes or so of tumble drying. Equally it might have been the increased heat of clothes drying - but disconnecting the heater element (both cooling things down and removing a big switching current) made no difference to the time it took to cut out.

I figured that if programmed machine logic was involved it would report a more specific error so the PF error is indicative of an unexpected power down. This got me thinking about the power supply itself. Sure enough, a thermal camera image of the control board in action revealed one very hot TOP242 IC. The shot here shows it still working at 110C but it will go past 130C whereabouts the built-in thermal shutdown trips. Bingo!



The TOPSwitch datasheet confirms the trip-point to be 130C to 150C and a ghetto-rigged fan proves the point finally keeping the machine going all the way through a 1 hour + drying cycle with the TOPSwitch staying under 50C.



Tempted as I am to bore a hole in the control box lid and mount the fan there full-time, it's obviously not fixing the problem at source. I think the most likely reason for the TOPSwitch to overheat would be the 330uF 400V input reservoir capacitor ageing. All the capacitors are suspect of course so the next step is to try and remove/test/replace as necessary. Unfortunately the PCB is flooded in the case with a clear potting compound that I'm not looking forward to tearing out. Will try and keep this posted.