Dishwasher saga part 3 (it wasn’t a microswitch!)

As I wrote in my previous post I was so happy when I finally discovered what’s wrong with my 20yr old . A faulty microswitch. Except that it wasn’t. The joy was over after a day and the symptoms returned:

  • When the heater was turned on or off, the dishwasher stopped.
  • If I opened or closed the door or hit it, it started washing again.
  • The symptoms were not repeatable – sometimes it was enough to hit the door one time, sometimes 5 times.

I disassembled the dishwasher for the 23rd time. Added a bolt to a microswitch to keep it in place (it was a bit wobbly). Nothing. Still random disconnects.

I almost went crazy.

Lastly, I disassembled the control board.

There are a bunch of relays (4) and one transformer soldered on the board.

I’ve run some advanced diagnostics (hit every relay with a screwdriver while washing).

Sometimes the left relay switched on/off, and sometimes it didn’t. So definitely, the vibration caused the switch. But which one is faulty? Again, there was no real pattern.

Lastly, I pushed the screwdriver between the transformer on the left and the relay (the one with the title NAiS 10A…).

Finally, a pattern! Whenever I slightly turned the screwdriver, which moved both elements, the relay switched the power off/on. Heureka! One of the contacts is bad, but which one?

I turned the board around and (still while running) I budged the relay and the transformer pins. On a second try, I found the loose one:

The solder break wasn’t visible at all (and I used a magnifying glass). It was the size of a hair. Only when I touched the pin with a screwdriver and moved it a bit, it disconnected the electric circuit.

I resoldered it and now the dishwasher runs as it should.

So it wasn’t a microswitch. And also it wasn’t a relay. When the big(ger) current flew through it (8A), it randomly disconnected.

P. S.: Wife knew the whole time. The first thing she said when the dishwasher started acting weird was: it is a ‘programator’ (a logic board).

Update 1 (2024-03-01) – resoldering again!

After a couple of weeks, the dishwasher started behaving strangely again. The washing cycle lasted up to 4 hours, which is not normal. The plates were greasy.

I disassembled it again, took the motherboard out and resoldered all pins of relays and transformers (around 15 of them). Now it works as it should, again.






6 responses to “Dishwasher saga part 3 (it wasn’t a microswitch!)”

  1. Rob Avatar

    @tomi great find congraz 🙂

    1. Tomi the Slav and 1024 others Avatar

      @rantanlan @tomi Yes, until next time … while disassembling the door I noticed the bottom rubber gasket is cracked and leaking a bit. The dishwasher saga continues!

  2. Pēteris Krišjānis Avatar

    @tomi "When the big(ger) current flew through it (8A), it randomly disconnected." I have seen such random behaviour with amount of current in the past. Also this was very interesting hardware debugging write up, thanks! 🙂

    1. Tomi the Slav and 1024 others Avatar

      @peteriskrisjanis @tomi The disconnects were clearly visible on the power graph too (now I recognize them), but before I didn't see the pattern.

  3. Tricia Avatar

    Great troubleshooting write up! I have a #Bosch dishwasher and love it. Definitely worth the time to fix.

    1. Tomi the Slav and 1024 others Avatar

      @SLOTricia @tomi Yes, we love it too, that's why I'm fixing it 🙂 No signs of rust after 20yrs. The best thing is, that it has only 3 programs (65C, 55C and 55C eco), we're using only one, so there is absolutely no decision paralysis 🙂

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