Repair: LG WF-T552A 5.5kg TurboDrum Washing Machine

In what seems to be just another day at the office home, something always manages to need my attention. This time, it was our washing machine which was behaving strangely. This particular machine was an LG WF-T552A TurboDrum 5.5kg with Fuzzy Logic which was handed down to us and saw a relatively hard life before we got it. It was probably due to retire for good, but my Dad wanted me to take a look at it to see if anything could be done to fix it.

The Symptoms

The first sign of problems was the first load of that morning. My Dad put the machine on, and left it to run as usual. However, the machine stalled early on in the cycle in the soak mode, and no water was running into the drum. Feeling like he was forgetful, he checked the tap on the wall and gave it a turn, and water began to flow in just fine. He concluded that he must have forgotten to turn on the tap.

Later on in that cycle, the machine stalled again at the rinse step. This time he recalls that the water flow into the drum was slower than usual. He chose to abort the step by jumping the machine into spin and completing the load so a second load could be started.

By the time the second load is attempted, the water flow was slowed down to a trickle. The drum would take an eternity to fill, and thus the machine was declared non-operational.

Troubleshooting

The first I found out about this issue was while I was riding my bike and came to a dead-end cycleway. I took out my phone to call Dad and inform him of my displeasure when he alerts me to something more to look at. After he informs me of the story, I immediately suspect either a water pressure, piping or inlet solenoid valve fault. The latter seemed most likely, but it felt important to exhaustively eliminate other possible causes.

As soon as I got home, I removed the hose from the tap on the wall and checked the water pressure and flow into a bucket. The water stream was a bit more turbulent than I expected, but the flow and pressure both seemed acceptable.

Removing the hose from the back of the machine, it seemed the hose assembly was in good order and flow through the hose was unimpeded. In the rear of the hose inlet, there was a grit filter which showed only minor residue – not enough to significantly impede the flow of water. A small orifice presented itself as the water inlet, and it too, appeared to be clear.

Having eliminated external factors as the cause, the fault is likely within the machine. I attempted to reproduce the fault through running a test load of washing. Immediately, the machine presented with a very slow trickle fill during the soak phase. Opening the tap at the wall further did not improve the situation, however, occasionally, turning the tap off and on again did restore full flow temporarily.

Diagnosis

Based on the symptoms, it seemed to me that this was a fault in the cold water water solenoid valve being stuck on a semi-permanent basis. Shocking the valve through changing the pressure did unstick it, but not reliably.

The operation of a water solenoid valve is quite interesting as only a small flow of water is controlled (the pilot jet) to change the pressure across a diaphragm to allow a larger amount of water to flow, as illustrated by the above diagram from Wikipedia by SimonOrJ. Bigclivedotcom recently posted a video about such valves and did a teardown.

Based on this, I suspect that the diaphragm is sticky. Either it remains shut and the slow flow of water into the drum is solely the pilot jet, or it is only partially opening, and thus causing a lot of resistance to water flow. This might be because the diaphragm is physically disintegrating (e.g. rubber turns into a sticky goo as it ages), or its physical properties have changed (e.g. it is not as flexible as it should be), or it is contaminated in some way to make it sticky (e.g. biofilms).

Whatever the cause may be, the first remedy that comes to mind is to replace the inlet solenoid unit. A quick search online shows that the solenoid assembly is still available for about AU$45 to $60. While this is not particularly expensive, it is still about 10% of the cost of a new machine. Considering the history of the machine, there may be a good chance that something else more expensive may well fail, and thus the investment into a new solenoid unit might not be justified.

Bright Idea #1

The first bright idea came to me as soon as I walked out of the laundry. Given that the machine has both hot and cold inputs, there are two solenoids. The machine itself doesn’t really know what we’re putting in – after all, older machines are pretty simple state machines (hence the “stalling” with no error feedback). As we are an energy conscious family, we normally wash everything with cold water only, so we really only need one solenoid to be operative to have a working machine.

Why don’t we just swap the hot and cold hoses from the wall, so that the cold water is entering the hot water port on the machine, and we tell the machine we are washing with hot water alone?

I thought this would be the simplest solution and require no extra work. Another test load of laundry was loaded, and the hot solenoid was verified to be operative. The drum filled for the soak just fine, and it did the wash …

But come time for the rinse part of the cycle, the machine once again stalled. The machine’s internal logic appears to be hard-wired to rinse with cold water only regardless of the water selection for the cycle.

Unfortunately, because of this, the simple workaround would not suffice.

Bright Idea #2

The next bright idea was a more involved extension of the first. As whitegoods often are still worth repairing, LG provided a helpful schematic on the rear to help us understand just how the parts of the machine are connected together.

The hot and cold water solenoids are marked H.V and C.V respectively. The drive appears to come from Orange and Grey wires, and return is via Blue. To my surprise, these were connected by a red and a blue connector.

If we swap the solenoid drive lines, so that the machine’s cold solenoid signal is connected to the hot solenoid, and we connect the cold water to the hot inlet, we should be in business!

To get access to the solenoid unit, it was a simple matter of undoing the top rear two screws (based on a hunch that the panel with the words “Fuzzy Logic” would be removable).

Inside, it’s clear that the solenoid unit itself is a module which is symmetrical – cold on the left, hot on the right, mixing together in the centre into a plastic part that diverts the water into the drum.

The connectors are colour coded as promised, and keyed as well. But they are interchangeable, except for one hitch – the hot lead is longer than the cold lead, so thus it makes it impossible to just swap the leads around without some extra work.

As a result, I grabbed some terminal connector blocks and stripped down some spare sheathed mains rated wire and removed the sheath. Using this arrangement, I was able to extend the cold solenoid valve control lines enough to reach the hot solenoid. As a washing machine is a fairly high vibration environment, crimping or soldering the wires may have been a better option, but this was somewhat more convenient given the tools at hand.

Another test load was washed, and this one completed successfully. The workaround cost practically nothing (maybe $1 in terminal blocks and wire scraps) and should let us use the machine for at least a little while longer.

Conclusion

Through the process of careful troubleshooting, the problem with slow filling of the drum was narrowed to a faulty sticky cold water solenoid input valve. Because of our usage habits, only one solenoid is necessary to achieve a cold water wash, and thus the signals were physically exchanged between the hot and cold solenoid valves to avoid the need to purchase any spare parts and bring the machine back into service as promptly as possible. An extension of wires was necessary to enable this workaround to be completed.

That being said, it doesn’t restore full functionality (e.g. hot or warm wash is not possible). The lifetime of the remaining hot solenoid is also unknown, along with the other pumps and motors that make up the remainder of the machine. Should the hot solenoid also fail, it’s probably a good time to take the solenoid assembly out and clean out the diaphragms and see if that restores functionality. If not, a whole replacement of the unit is probably the next best option short of replacing the whole machine.

All in all, it was a pretty interesting project to have undertaken – it’s not everyday you make an improvised hack to keep a washing machine going.

I also did make an improvised hack of an LG fridge that didn’t get posted – this one had constant beeping and random front panel button activation, so I disconnected the front panel which rendered the unit silent but with a loss of manual temperature selection. The fridge continues to serve us today, over eight years since the modification. It’s probably a win for the environment too – waste averted!

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
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