My parents have a Smeg dishwasher that resets itself, at some point through a cycle so it loses it's place and start the cycle again or just doesn't complete the cycle leaving itself un-emptied. The pump runs, it's not stuck. They've been advised it sounds like the control PCB but as I'm a sceptic, I want a second opinion, especially given that they've been quoted 250 to replace it, anyone care to offer an enlightened opinion or tips to prove or disprove the advice?
Check the PCB for bad joints, particularly if it's post 2006, so manufactured using the dreaded lead-free solder ...
Places to look especially hard, are on the pins of relays, and any semiconductor power devices, which will be typically in a TO220 style package (three legs, black square plastic bit, metal tab at the back with a hole in it) and connectors. If the controls are mounted in the door, it's also quite common for the wiring loom to suffer problems at the hinging point. The actual wire breaks from metal fatigue, but it is, of course, inside the plastic sleeve of the wire, where you can't see it. Such breaks can give intermittent symptoms of all sorts of descriptions.
If you can (carefully, bearing in mind that there will be mains on the PCB) run the machine so that you can gain access to the PCB, you could try 'provoking' it by having a firm tap around with the butt end of a hefty screwdriver. If you do get a result doing this, you can narrow it down a bit then, by changing to a Biro pen to do the tapping, or a piece of wood dowell to apply controlled pressure to various areas of the board. This is, however, just general advice, as boards made with lead free solder, are far less 'willing' to reveal the locations of bad joints using these traditional methods, than good old leaded solder boards were ...
Of course, anything carrying more than signal level or generating heat or fixed to heatsinks/off board hardware etc...
Hadn't thought of that but now you mention it, it's obvious... Thanks.
I'm used to working on energized PCBs, I used to repair TVs then monitors and PC PSUs then system boards (when they were worth money) and finally automotive diagnostic equipment...
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