Lavamat 74620-W door problems

[IanR7777]

Hi,
I own a AEG Lavamat 74620-W product number 914001304

The washing machine works fine except for two things;

1) The door does not unlock at the end of a wash cycle (it requires the emergency release by the pump drain)
2) The door automatically locks as soon as the wash program selector is turned. Previously it locked when the START button was pressed

There are no error codes shown on the display.

I have removed the door lock and tested the three connectors with a meter. Both of the two pin connectors which I assume are switch interlocks seem to be opening and closing with the operation of the lock. The three pin connector that I guess is the door lock activation solenoid has sensible resistances across it.

Next I checked the pressure switch the pipe connecting it to the drum is clear. When I connected a syringe to the pressure switch I could hear it switch. (open & close with pressure changes)

I suspect the electrical functions of the pressure switch are ok, as I have no error codes and the machine is working and not flooding ?

I am left thinking that the door locking problem must reside on the main control board. As the control board thinks there is nothing wrong, but is itself sending a faulty “always lock” signal to the door lock.
I have removed the main control board and there is no obvious signs of damage to components. It looks like the door switch is driven by a Triac and a relay.

A few Questions.
1) Is it likely that a faulty Triac could be the cause of the problem.

2) Its difficult to buzz the board through with a meter does anyone know how the Door solenoid is activated for a 74620 ?

3) I have read on some forums that AEG store extra “internal” error codes that can be accessed by pressing certain buttons, anyone know if this works with a 74620

Any other help or ideas would be greatly appreciated.

[IanR7777]

Re: Lavamat 74620-W door problems

Boy this problem is giving me a headache.

Placed a meter across the TRIAC on the control PCB. It looks as if when I close the door (with a program selected) the PCB is momentarily firing the TRIAC. The TRIAC is not shorted open as I suspected.

This means the PCB is commanding a door lock, does anyone have an idea how this could happen without throwing up another error code.

Ran the machine last night it works perfectly except that the door remains closed at the end of a cycle. And auto locks when closed before a start is commanded.

At the moment the machine is fully operational but requires an emergency release to open it 🙁

Pressure switch (three position) and door switches fine, is it possible that the tacho circuit is detecting a low level voltage that makes it think the drum is in slow rotation. Or should this throw a code ?

I noticed a number of previous posts with the same problem on the WEB but no solutions.
Any help or ideas would be welcome

[CJAPeterborough]

Re: Lavamat 74620-W door problems

You can eliminate the tacho idea by unplugging the motor?

It does sound like a faulty pcb though…….

[Seamy]

Re: Lavamat 74620-W door problems

try replacing the door switch first, its the cheapest option, test motor & heater for earth faults as they can throw up erroneous faults

[IanR7777]

Re: Lavamat 74620-W door problems

Thanks for the reply. I have located a service manual now for my machine and I am 99.9{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} sure that the door switch is OK as it completely checks out. (Coil resistances and interlock switches).

I have noticed on other forums that this fault has appeared many times on AEG machines and so far no one has found/published a solution.
(It seems that AEG have sold quite a few door locks in the pursuit of a solution)

I am planning to check out the motor tacho circuit tomorrow.

My initial checks seem to show that when I close the door and select a program I am getting an spurious “shut door command” from the micro-controller. (the close triac fires, with just one pulse)
Why it is commanding a close door without throwing a code makes me think that it thinks its in an operational mode that requires a closed door ?

Unfortunately the service manual does not have the circuit diagram for the control board so I will have to figure it out with a meter.

At £300 the control board is not a viable purchase for this machine. But the machine is in excellent condition, so its worth spending some time.
I have located some second hand boards but they are all on Ebay in Germany !!!

[Seamy]

Re: Lavamat 74620-W door problems

without being repetitive

try replacing the door switch first, its the cheapest option, test motor & heater for earth faults as they can throw up erroneous faults

[Author]

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