LG Washer/Dryer Power Fail

[AdrianM]

Re: LG Washer/Dryer Power Fail

Yeah, no wonder most of the YouTubes for this kind of fault are coming from Spain. Up here in blighty we rarely see more than 20C but interestingly, we've just had a record 30C+ summer and surprise surprise this is when the cutting out started!

[budm]

Re: LG Washer/Dryer Power Fail

What is the Voltage and current rating as printed on the FAN?

[AdrianM]

Re: LG Washer/Dryer Power Fail

A few observations about these LG washer dryers while I'm waiting for parts to show up :-)

The Direct Drive drum motor is pretty neat and seems quite well implemented. The motor inverter is powered by the 330V DC obtained from the 330uF/450V capacitor. The spec gives it as drawing 440Watts at max load. Speed is smoothly variable and very quiet compared with other brushed motors I've experienced in this kind of application. It uses hall effect sensors to determine the relative positions of the rotor and stator so the drive is very efficient.

The smaller fan motor is also brushless but unlike the drum, has no magnetic sensing. I don't think it has back EMF sensing either as at start-up it clatters briefly as the driver probably blindly switches the poles until the rotor catches up. I'd scope it to find out but...

The worst part of this design for me is the non-isolation of the control electronics to the mains. When I first looked at the PCB I noticed numerous Opto-Isolators and thought "Oh good, it has Isolation to make testing safer". Wrong. I think they used Optos as level-shifters only. The Brushless drum motor necessarily runs off the rectified mains supply to get the hundreds of Watts needed to spin several kilos of laundry at 1400 RPM.

The other odd (at least to my engineering eye) thing is the power switch. I'm used to Led illuminated push-buttons for power switches on domestic appliances being low-voltage contacts operating something in the logic section. On these LG's the switch is a change-over connected to AC live via a 220 Ohm resistor. Pressing the button connects AC live via 220R to the main rectifier feeding the 330u 450V capacitor and the TOPswitch PSU. This is an enforced soft-start I guess, and when the micocontroller gets going, it drives a power relay that bypasses the 220R and routes AC live both to the PSU on the PCB and the heavy heater loads. These loads are switched to neutral via other relays.

So it bootstaps up but how does it shut down? The change-over contact normally routes AC live to an Opto LED via 220K so when the button is pressed to turn off the machine, the microcontroller can detect the event via the Opto and when it chooses power-down the main relay. It turns off the panel lights straight away but waits a while before turning off fully. This means the opto is always on when plugged in giving a standby current of about 0.2 Watts - or about 20p a year ;-)

While I can't fault the washing part of the machine, the dryer part has problems. Apart from the low-spec PSU components responsible for powering the drye fan, the machine needs major dismantling a couple of times a year to clear out accumulated lint. The system circulates heated air through the drum and on its way round cold water is injected to condense moisture in the air and the whole lot (including lint) is supposed to end up in the sump where it's pumped to the drain. The lint is supposed to collect in the pre-pump filter where it can be retrieved.

But it doesn't all make its way there and builds-up in the heater box (next to the element!) and in the circulating trunking. This is why there are loads of YouTubes showing how to open up the machine and clear the trunking. I think some models now have a large removable filter screen conveniently located in the opening of the door. I'd be looking to replace ours with one of these some day.

The heater is a bit odd too. There is a thermal cutout (non-resettable) and a bimetallic cut-out with a trip-point of about 150C both in series with the 1.5KW heater element. However, the latter never seems to get used as the dryer has two thermisters monitored by the microcontoller and it controls the heater relay to limit the airflow to 100C on its way into the drum. I guess it could be an "abundance of caution" but if the machine fell back on "bang bang" control at 150C I'd like to know and the logic implies it wouldn't know.

One nice thing is the test mode that's been useful diagnosing my issues. This allows, among other things, you to run the dryer on its own and view the circulating temperature and fan speed. Very handy.

[AdrianM]

Re: LG Washer/Dryer Power Fail

What is the Voltage and current rating as printed on the FAN?

Nothing printed on it. The three poles all measure 4 Ohms but there's no other spec I can find.

[redwire]

Re: LG Washer/Dryer Power Fail

Appliances are expensive now and so much e-waste generated from them being tossed out.
People take an $600 repair estimate for their $2,200 appliance and decide to "buy a new one". A year later the model is discontinued.
The whole industry is about selling new appliances.

Everyone wishes the design was better, reliability was higher, and repair guys want them easier to troubleshoot.

The South Korean appliances (LG, Samsung) have innovation but they go down the rabbit-hole on some engineering.
Their fridge compressors are crazy complicated to get a few % better claimed efficiency and they just make the warranty period.


Since clothes dryers can be a fire hazard, they have the safety high-high limit switch and redundant temperature sense. It's a requirement for functional safety.

The current-limit graph Fig. 54b is scaled only for the Y-axis, so a TOP242 at 0.45A is 50% of a TOP243Y or 33% of a TOP244Y.
Like Fig. 6 values. I'm assuming it's a (Y) TO-220-7 package you have.

TOP244Y seems at the limit of big, going from 1.35A down to 0.45A (~45kohm) is the lowest current the part can do.
I would try TOP243Y and 16.5k-19k for the resistor. The current-limit accuracy is +/-7% for the IC, so 16.5k is for a low bogey to keep at least 0.45A available. The transformer can take a bit more anyhow.
Can you post your control board part number, for the search engines.

[AdrianM]

Re: LG Washer/Dryer Power Fail

I just can't be doing with carting a machine that's 99% functional to the scrapyard for the sake of the 1% of its faulty components that stop it from working (says the man with two 25 and 50 year old cars in his garage awaiting repair). The S.Korean joke is the big sticker on the front boasting a "10 Year Guarantee" on the DC Motor. If there's no way the rest of the product would last that long it's not a lot of help although if it did come to scrap I would definitely recycle that motor for something - a wind turbine or E-bike perhaps.

I can confirm that the switcher is a (Y) TO-220-7 part:



and I think the board ID is EBR658736:



Looks like my machine will be the lab-rat here as I've got a TOP244Y on its way as I figured it was the lowest on-resistance part that could be limited down to 0.45A. You seem to agree with that, and I'm sure the transformer primary would handle a teensy bit more current if required. In the thermal image the transformer is pretty close to ambient, and I'd like to get that 22V fan supply higher than the saggy 18V it is now when loaded.

To do this I'm prepared to tweak the resistor between 33K and 47K while keeping an eye on the transformer temperature.

[sam_sam_sam]

Re: LG Washer/Dryer Power Fail

I am watching this post and what happens next when you put in the new switching IC chip
Keep us posted

Thanks

[lti]

Re: LG Washer/Dryer Power Fail

That looks like a TOP246 to me.

[redwire]

Re: LG Washer/Dryer Power Fail

Um, I also see TOP246YN in the pic. That is a 2.7A, RDS(on)=2.60R. Upgrades would be different than what we've been talking about; TOP247,248,249

Can you do a load of laundry AND dry a load at the same time? That seems like it would load up the PSU.

[stj]

Re: LG Washer/Dryer Power Fail

how could he "do" a load and "dry" a load at the same time? it only has one drum.

[CapLeaker]

Re: LG Washer/Dryer Power Fail

I see what redwire sees. That isn't a TOP242, it's a TOP246! So you need a new switcher first!!!

[AdrianM]

Re: LG Washer/Dryer Power Fail

Oh! I really done goofed. I can't begin to explain what led me to read that wrongly. So now it's even more baffling...

Going back to my plug-in power meter test, and seeing 8 Watts from the AC input then @ 80% eff., the baseline load supplied by the TOPswitch when the machine is idling is just 6.4 Watts. I can then easily and repeatably get a 80C+ rise on the part by adding 13.5 Watts of load by running the dryer fan for 5 minutes. This takes the IC from around 60C when idle up to the ~140C trip-point. Surely even the TOP244YN should manage 20 Watts without this much drama?

[CapLeaker]

Re: LG Washer/Dryer Power Fail

The IC shouldn't be at 60C at idle. That is a very hard pill for me to swallow on a TO-220 that has a heat sink on it. Id say the TOP244 would be running at full tilt at 20W.

[redwire]

Re: LG Washer/Dryer Power Fail

I think the IC can get too hot from the SMPS having low efficiency or heavy load. The thermal IR camera can show if another part is stealing output current.
But running hot with low loads on the PSU?

Power Integrations AN-14 lists reasons for a TOPSwitch to overheat. As budm mentioned, the snubber zener can apparently cause trouble too. So there are some supporting parts to check.

[momaka]

Re: LG Washer/Dryer Power Fail

The S.Korean joke is the big sticker on the front boasting a "10 Year Guarantee" on the DC Motor.

Yup. I know that all too well, as I have a slightly older LG washer myself. 10 years warranty on the DC motor (the part that is absolutely NOT going to break anyways). Mine shot its drum bearings at 7.5 years old - I guess that's not too terrible. Still, considering how little load we've put through it, I think it's laughable. My sister's Candy washer (overseas) is about to turn 25 years old and never needed anything serviced. Still works like a champ and goes through at least 2-3 full loads daily (it's a smaller washer made for European standards). The Candy washer we had before that one made it to 20 years before its coated steel drum enclosure rusted away. And my grandmother had a GDR (East Germany) -made washer that gave trouble-free operation for 30 years. So I think that puts a good perspective on how low the quality has gone with today's appliances.

Still, I agree that it's not worth discarding an appliance over a tiny failed part. With the case of my LG washer, I replaced the bearings last year (after I could no longer stand the freight-train noise the washer made with those shot bearings for nearly 2 years ). Works okay now. But when I looked at it while it was disassembled, indeed there are quite a few engineering design goofs (e.g. drum cover has non-smooth back, which tends to collect water and then grow mold over time - absolutely silly!).

[AdrianM]

Re: LG Washer/Dryer Power Fail

I think the IC can get too hot from the SMPS having low efficiency or heavy load. The thermal IR camera can show if another part is stealing output current.

Thanks for the vector to the AN. I noticed that the output diode for the fan supply also runs very hot. I can't find the part's spec. it's case code is 3L2 125 It measures 0.46V forward drop on the diode test range. I guess it's a fast recovery Silicon diode not a Schottky.

I did briefly try a 1N5822 (40V PIV Schottky) in place but the actual PIV must have been too high because it went into break-down. Good thing the current limit(s) kept things sensible. I've swapped it for a 2A 100V PIV Schottky in the same SMD package size and that's running cooler already.

I went over the PSU circuit once again and found another CR snubber that I'd left off my first schematic (R241, C241). I've also corrected some part ID's.



I've now desoldered most of, and tested all of the individual parts around the TOPswitch and nothing has been out of spec. DZ241 is a 180V Littelfuse TVS so I took it out and tested it with a scope using the flyback from a relay coil. Sure enough it clamps at about 180V. I'm pretty certain there's nothing wrong with any of the supporting parts although I have replaced the big DC cap CE72 with a EPCOS / TDK B43545A5337M000 becuase the original has probably clocked-up enough hours already.

I've got to wait until next week for the replacement TOPswitches to show up.

[AdrianM]

Re: LG Washer/Dryer Power Fail

With the case of my LG washer, I replaced the bearings last year (after I could no longer stand the freight-train noise the washer made with those shot bearings for nearly 2 years ). Works okay now. But when I looked at it while it was disassembled, indeed there are quite a few engineering design goofs (e.g. drum cover has non-smooth back, which tends to collect water and then grow mold over time - absolutely silly!).

Oh, perhaps I have that to look forward too :-( Pretty major disassembly you took on there!

[AdrianM]

Re: LG Washer/Dryer Power Fail

I was just thinking slightly differently about the overheating... the T0220 heatsink looks to be about 12C/W and it's getting to 120C over ambient therefore the TOPswitch is dissipating something in the order of 10 Watts. The converter efficiency should be something like 80% which implies an active load of 50 Watts. But I know the AC power going in is only half this when the switcher overheats - so it has to be that the TOPswitch is only running at 40% efficiency for whatever reason.

I know this is just more "spinning the wheels" until I get to try a new IC but I felt like writing out the figures here so I can keep track of the process.

[petehall347]

Re: LG Washer/Dryer Power Fail

Thanks for the vector to the AN. I noticed that the output diode for the fan supply also runs very hot. I can't find the part's spec. it's case code is 3L2 125 It measures 0.46V forward drop on the diode test range. I guess it's a fast recovery Silicon diode not a Schottky.

is d243 not a zener ?

[AdrianM]

Re: LG Washer/Dryer Power Fail

D243 was a Silicon but is now a Schottky. I finally extracted the TOP246Y:


And replaced it with a TOP248Y plus 12K resistor in series with X pin to maintain the current limit (plus a little bit):


So now with the Fan running, after 30 minutes it's only getting to 47C and not tripping the thermal shutdown anymore:


I'm coming around to the notion that the dryer fan bearings are worn and putting extra load on the PSU. When I monitor the supply rails with and without the fan running I see the following:

[Ideal] Idle -> Fan running
[12.0] 13.1 -> 13.2
[16.5] 16.0 -> 15.9 (Feedback tap)
[22.0] 23.7 -> 19.5 (Fan supply)

(Ideal is what is printed on the silkscreen against each rail)

Feedback is from the "16.5V" rail so that rail stays closest to the design ideal. The Control input circuit is pretty slack though - using 9.1V Zener (ZD242) plus a diode drop (SD241) plus Control pin input current of 6mA * R243 to maintain 5.8V at the C pin resulting in a theoretical stabilised output of 16.2V

Anyway, this TOP248Y upgrade has indeed remedied the "Power Fail" problem for now, and as everything else is working correctly I can keep an eye on the Fan and see if it continues to draw more and more current (unless it falls apart first).