Tumble dryer on the blink

[DiyNutJob]

On my bosch WTL5400, the programme selection knob is on the blink. It would select the wrong programme, or suddenly selects another programme stopping any programme already running. Repeated turning of the knob, or repeatedly running whatever programme it selects will eventually cause it to settle down to the correct programme. This could take anything up to 20 minutes. My initial thinking is that whatever electronic dial the knob is attached to is broken. The other possibility is that a capacitor is blown and taking longer to charge up. Once charged up, then everything is working fine.

Any ideas on this please?

Left photo shows the knob selecting the correct programme. Right shows the wrong programme selected. No other buttons or knob is used apart from the power button.

 

[Harry Bloomfield]

This could take anything up to 20 minutes. My initial thinking is that whatever electronic dial the knob is attached to is broken. The other possibility is that a capacitor is blown and taking longer to charge up. Once charged up, then everything is working fine.

The switch, sounds like a rotary encoder to me, either a simple mechanical switch, or an opto version. My first step would be one of checking and cleaning that encoder.

 

[DiyNutJob]

The on-the-blink knob is attached to something marked "2" and "PA 6-6F 25". I think 2 means it's the second dial. The smaller knob is attached to the same looking thing marked "1" and "PA 6-6F 25". Are these standard components and can be bought?

 

[Harry Bloomfield]

Are these standard components and can be bought?

It appears not.. See if you can see any sort of contacts, swept by the rotation of the dial. If you can - Try a spot of contact cleaner, on plastic parts in the area, to see if any are damaged by the cleaner, if none - give the contact area a good spray to clear any debris. Let dry, reassemble, and test.

 

[DiyNutJob]

Turns out to be a bunch of micro switches and a mechanical combination press'er. The problem likely to be in the latter, with some of the pressing "fingers" bent by time and wear.

 

[Harry Bloomfield]

Turns out to be a bunch of micro switches and a mechanical combination press'er.

Thanks, and oh dear..

Forget the previous suggestion. The best bet, is to replace those push buttons with new. They are quite cheap, but some soldering involved, if the OP is up for it. Still no guarantee, that it is the issue.

 

[DiyNutJob]

Fixed. All the micro switches measured fine from a direct press, and none were faulty. First I bent the those metal "fingers" away from the switches. None of the switches got triggered. Then all the "fingers" were bent towards the switches. The measurements didn't look convincing. But, these worked fine once back on the machine.

Now, I expect the machine to go another 30 years

The button press'er runs on plastic train tracks that rise and fall.

 

[DiyNutJob]

Turned out the problem was caused by a faulty micro switch. When pressed, the switch had a continuous variable resistance. This gave the impression to the machine that the programme dial was being turned intermittently. Whenever the dial was turned, the machine stopped to wait for user to give the go ahead for the new programme.

The problem was fixed with a new china micro switch.