Indesit vented tumble dryer control board dead

[notallbad]

Anyone able to help diagnose the fault with this board please.

Hopefully photos are clear enough to give me direction on what readings to take and where.

All ancillary components of the dryer have been tested and work i.e heating element, thermostats, sensors, motor, door switch, wiring harness.

So theres 230v at the control board but no life whatsoever with or without the ancillaries connected.

The on/off/timer dial contacts are clean and make good contact. All the through hole mounted components appear to be good i.e diodes, resistors, caps, relays and transformer.

Did find a faulty smd diode on the xformer secondary side but still no luck after replacing with a good one from an identical donor board.

[notallbad]

Wiring connections

[stj]

forget the board and check the door switch and thermostatic switch(es) first.
btw, any excuse to waste money these days, my vented dryer just has a motorised camswitch instead of that microcontroller/relay crap

[notallbad]

Yh door switch etc all checked. But in any case even with those disconnected the board should still power up when the dial is turned to select the drying duration.

The door switch only prevents the motor from activating as a safety feature so board should power up still.

[stj]

yes, but the thermostatic switches are different, those are a final safety before the heater catches fire.
those can shut down a lot - maybe even the control board.
and they do burn up - i had to replace one of mine.

they are mounted in the airflow to make sure the heater doesnt burn up from a blocked vent or overloaded drum.

why not check for 5v or 3.3v on the microcontroller?

[notallbad]

Have already stripped the machine down, thoroughly cleaned it out and tested all ancillaries, as its a vented dryer theres not much to test but everything else is ok.

On the regulator 1117m3 the voltage appears to be dropping in and out, it appears as though its in a boot loop.

The microcontrollers on the board are:
LNK626DG
SENO12DG
LM293

[redwire]

The LNK626 drives the low voltage power supply with T1, it should have a 12VDC output for relay power. This usually gets dropped down to 3.3 or 5V for the MCU by another IC like the '1117.
Check the input to the '1117 and if unstable (and IC is not hot), it's got at least 4 different makes of electrolytic capacitors, I would check the six. C50 has mains and can bite.

[notallbad]

So just a quick update on progress.

I felt that as the Lnk626, Sen012 and Lm293 were 'boot looping' there was another cause preventing start-up so starting looking elsewhere.

A few components later and its got life back into it (yet to be tested back on the dryer).
NE555 timer and smd cap
A couple of transistors
Couple of smd diodes

To be honest I think a shorted smd cap took out a couple of diodes, suspect the ne555 was ok but I had some so swapped it out anyway.

Shall update once fitted back in the machine and tested.