LG Washer/Dryer Power Fail

[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.

[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.

[lti]

Re: LG Washer/Dryer Power Fail

That looks like a TOP246 to me.

[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

[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.

[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

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.

[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.

[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

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!

[momaka]

Re: LG Washer/Dryer Power Fail

Wow. 13.5W on a part designed for 15W.... that's really pushing things too close. No surprise it's failed after a few years. Perhaps if the PCB was designed with more heatsinking, the TOP242 might have lasted a little longer (or a lot more).

I agree with the others that a TOP243/244 is probably the best route to go. But nevertheless, I still think it would be a good idea to attach a large aluminum heatsink/heatsink on top of the new chip. PCB cooling could still be marginal, even if the new TOP243/244 chip has lower dissipation.

[AdrianM]

Re: LG Washer/Dryer Power Fail

I can get a TOP244 here by tomorrow and the laundry is piling up ;-)

@redwire, looking at Figure 54b the scaling factor is 0.45 for TOP242 so with X at zero Ohms the transformer primary is current limited to 0.45A.

To get the same limit for a TOP244 with a scaling factor of 1.35, am I right in looking along the Y axis for 0.45A/1.35 = 0.333A which seems to be around 39K?

[CapLeaker]

Re: LG Washer/Dryer Power Fail

Sure looks like the PSU isn't able to supply power as it should. Forced obsoleteness, I say. If it were mine, I'd recap the thing and get a top242 and a top243 and see what happens with a new top242 in place. I also think that the current top242 may have cooked itself so many times, that its characteristics changed a bit. Probably the top243 is the answer at the end, but I'd be curious if a new top242 would run this thing again like it was before.

[AdrianM]

Re: LG Washer/Dryer Power Fail

Here's my test of the fan motor power. I pulled D423 off the board and jumpered it onto a breadboard with a separate 1000U cap to GND. From here I measured the current at 0.73A and volts at 18.3V so the fan motor alone takes 13.5 Watts. Resistance in all the dangling wires probably means more like 15 Watts when the diode is back on the PCB.



Plugging the machine into a power meter adapter shows 25W going in during this test and at idle it's 8W all of which can only be supplied via the TOPswitch. So a delta load of 13.5W shows up as 17W at the input so the convertor efficiency is as expected at around 80%

This makes the output power around 20 Watts if the input power is 25 Watts so I think however you look at it the TOP242 Y is being pushed too hard. It looks like redwire's suggestion of substituting a TOP244 is going to be the way forward, and as it's a T0-220 I can series-in a resistor with the X connection to stay with the original transformer design parameters.

[budm]

Re: LG Washer/Dryer Power Fail

Also verify the RCD snubber for that SMPS IC are still OK.

[redwire]

Re: LG Washer/Dryer Power Fail

Assuming the very hot IC is the problem, and not a side effect due to low line voltage or a bad electrolytic capacitor CE72, CE244, CE242 etc. I would say the IC needs cooling from extra PCB copper, or a heat sink/bigger package. The conformal coating over it acts as an insulator. A stressed/aged IC can have higher on-resistance and shifted current-limit so it cooks itself.

You can try add a heat sink or replace the TOP242. I would put in a TOP243 and extra resistor, to get 1/2 the heat.

With the "X" pin is connected to the source, then the part operates at max. current limit.
TOP242 is 0.45A and a TOP243 is 0.75A so going to the TOP243 it's best to add a resistor at X-pin to prevent the transformer from saturating. From Fig. 54b a 13k resistor from "X" to "S" will keep the same old 0.45A current-limit as a minimum. But the bigger part runs cooler with 1/2 the on-resistance.

Wait - the "X" pin is not brought out on the DIP-8 or SMT-8 package part, so this idea wouldn't work for that. Unless this the TO-220-7 packaged part TOP242Y ?

[AdrianM]

Re: LG Washer/Dryer Power Fail

So this thing turns out to be "hot" everywhere. I traced out the front-end and AC Line voltage is but a diode-drop away from the so-called GND bus. GND isn't actually tied to chassis but it makes it hard/risky to work on.



My line isolating xformer probably won't handle the power of this thing so I'm going to have a tough time powering the 22v circuit independently or checking the ripple with a scope.

The TOPswitch is configured for half-frequency operation (F connected to C) and Line-sense and External Current Limit Features Disabled ( L & X grounded). It's also a bit weird around the flyback snubber and output control sensing areas. Do we still think a TOP243/244 would drop in here?

[momaka]

Re: LG Washer/Dryer Power Fail

The fan seems to spin freely and measures 4 Ohms across each winding so appears to be in spec.

That doesn't matter.
As the fan is loaded, the current draw will change. On that note, check if there are any dust filters behind/in front of the fan. If they are clogged, they would cause it to draw higher than normal current. (Hint: always clean fluff from your dryers ).

I just ran the dryer while measuring the 22V rail. With the fan off it's 24V then drops to 19V with the fan on. I guess I could cut a track between the 22V reservoir cap and the fan driver and measure the DC current - although I'm not sure what it will tell me without knowing what a "good fan" should draw.

Going from 24V and sagging down to 19V is pretty sad (though not necessarily bad).
It doesn't matter if you don't know what a "good fan" should draw. If you know how much current the fan is drawing and you know the voltage it is running on (in this case, 19V under load), then you can tell how much power it is drawing (Volts x Amps). From this, you can figure out if perhaps the fan is drawing near maximum design power of the TOPSwitch IC, which is 15W as mentioned by rewire in post #8 above).

That said, YES, you can cut a trace (or remove the rectifying diode) for the 22V rail and insert 20V DC from a laptop power adapter there. Then you can measure the current draw on that rail much easier... and then determine if it's getting close to the maximum of what the TOPSwitch can handle.

(But again, make sure you use an isolated laptop adapter... or just one with the ground pin floating, so that you can tie the adapters ground to the washer's ground. I imagine the washer's PSU ground is already connected to earth ground of the house wiring. But nevertheless, I always like to have only one ground entry point for avoiding ground loops and noise.)

[stj]

Re: LG Washer/Dryer Power Fail

maybe the cap is going and cant handle the high frequency ripple caused by the motor driver.

[AdrianM]

Re: LG Washer/Dryer Power Fail

Unfortunately the dryer fan is actually a brushless motor so there's a three-phase inverter driver. Also the machine logic is monitoring the fan speed via a voltage summer/comparator and will halt with an error if the fan isn't detected. I was trying to test the PSU with the fan unplugged when I discovered this.



(image from servlib.com/lg)

The fan seems to spin freely and measures 4 Ohms across each winding so appears to be in spec. I just ran the dryer while measuring the 22V rail. With the fan off it's 24V then drops to 19V with the fan on. I guess I could cut a track between the 22V reservoir cap and the fan driver and measure the DC current - although I'm not sure what it will tell me without knowing what a "good fan" should draw.