Dishwasher repair

[Simon Black]

This morning I found our dishwasher with a blank LED display but with the sound of the drain pump running. Switching the power off stopped the pump and it appeared that the machine had completed it's wash cycle with no water left in the bottom of the machine.

I've now had a chance to take a better look, given the lack of LED indications, I suspected a problem with the controller. Opening the controller I found a relay with obvious scorch marks

As well as an IC with a hole in the top, making identification tricky! The chip seems to be connected to the coil side of the relays.

The control module is a Bosch 00642724 from a SRS45E42GB dishwasher.

The question is, what are the chances that just replacing the controller module will fix the machine? Or is it likely there is another fault (that caused the failure of the control board)?

Has anyone seen anything similar in the past?

I'm trying to decide whether to invest in a new control board, or just replace the machine.

Suggestions welcome!

Simon

[newshound]

I'd base my decision on the age and condition of the machine. I'd consider replacing the machine if it is over 6 years old.

[misterroy]

[SH]

that is a lucky find for the OP :-)

To the OP, watch out for "Customs charges" as well as the postage and packing, which can easily all add up to double the listed part price :-(

[Theo]

That shows the blown chip as a ULN2803:

The relay is a Song Chuan 899-1C-F-C-6VDC which isn't showing as in stock at a UK distributor: maybe there is a drop-in replacement from another manufacturer. It's a 6V coil, pinout here: For a quid for the chip and a few quid for the relay I might try replacing them and see if it fixes it...

Theo

[SH]

I'd also check the coil protection diodes in case they have gone O/C as they are critical for preventing back EMFs.

I'd also examine the old relay to see if its the coil that burnt out or whether the contacts burnt out and possibly arced across to the coil sending mains voltage back to the IC controlling the 6V coil.

Either event coudl cause a hole to be blown in the IC.

[Harry Bloomfield, Esq.]

misterroy expressed precisely :

It doesn't look like the same part!

[Dave W]

In future, could you reduce the file size of your pictures from 37.5MB to 100KB? I have to wait while the picture downloads line by line.

[newshound]

+1. 1MB is plenty even for big fancy monitors.

[Simon Black]

Where did you get 37.5MB from? The files I linked to are 783kb and 1.2MB.

[The Natural Philosopher]

Indeed, but drop box is incapable of serving them with any speed

[Simon Black]

On the burnt relay, in circuit the coil measures approx 2k, the datasheet quotes 100R so it's safe to say it has gone O/C. The contacts are 'stuck' in the energised state too, but given the state of the relay body this is no surprise. There are two more relays of the same type on the board, these both show the expected coil resistance. I have also checked the contacts on one of the other relays, in the N/C position they measure around 30R, tapping the relay changes the resistance - not ideal!

The datasheet for the ULN2803 shows it has internal protection diodes for driving relays, so a failure there could certainly kill the driver chip.

Senior Domestic Management (aka SWMBO) favours just buying a new dishwasher. As this one is 10 years old, that might be the best solution for a quiet life!

[Simon Black]

So it seems.... Uploading the files was much faster than downloading them to check the sizes hadn't changed! Shame Tinypic no longer operates as that seemed better.

[Sysadmin]

Check the underside of the board for solder tracks, that may have caused a short circuit.