OK, thanks for the update and will check back.
Yes, the big white rectangluar one - it's ceramic so feels like unglazed potteryHi,
no not checked that, is that the big white one, should I de- solder it to test it.
Thanks for the advice.
After a close read, I can see that there has been a lot of very extensive and high quality testing Impressed.
Eddie49 said something that is confusing me :-
'The results that I was not expecting are when the transistor was out of the board. The upper end of R4 stays at 1.4 volts,'.
Was this the voltage measured with the transistor out of the board ? If it was, we've got something wrong somewhere with what is being measured. There should be 0V across R4 when the transistor is removed. Another issue is that the circuit diagram I'm looking at shows R4 as 10 ohm not 100 ohm as is printed on the PCB.
There's a 2A fuse in the circuit diagram and a fuse on the board, the circuit diagram shows the fuse is connected to a bridge rectifier but there is no bridge rectifier oin the board...
We could be chasing our tails here making an assumption that the PCB and the circuit diagram are matching.
It's been shown that the motor does spin when the anode and cathode are shorted out on the SCR (which is a TYN142 in the diagram) but labelled as a BT151 on the PCB...
We've got a map of Warsaw but we're driving in Beijing !!!
Yes, I think you are correct, a lot of joints were re-soldered, a new thyristor fitted and the MPS 42 transistor legs were cleaned and re soldered back.I'm just wondering if it was a dry joint and all the soldering/unsoldering has cleaned it up and that's why it's now working.
Looking at the funny stains on the underside of the board and the weird discolouration of the transistor legs and the general muck, it looks like the board could have suffered water/dirt contamination at some point and this could lead to the dry joints.