Help diagnosing DC Motor Speed Controler

[gilligan]

It was blowing fuses.

Put the meter to it and the center pin of these "Mosfets"? are shorted to each other, which is the AC line... which would blow fuses obviously.

Looking around I can't really find the datasheet on that A69104 but looking at the rest of the circuit to see if it is something else (because both of them are shorted from center leg to left leg) I find that the MOV is shorted as well.  This is going between the two center pins which would explain why they are shorted.  Maybe the left and center should test shorted on that A69104?

I know these aren't the best pictures but it's what I got right now.

[Andy Watson]

A69104 - they're not MOSFETs, they're SCRs, thyristors.

https://www.radwell.co.uk/en-GB/Buy/KB%20ELECTRONICS/KB%20ELECTRONICS/A69104

Allegedly the same as a S4020L
https://www.futurlec.com/Diodes/S4020L.shtml

I would expect to measure something between the gates and cathodes - it depends on the circuit.

I find that the MOV is shorted as well. 

Are the SCRs still shorted when the MOV is removed from the circuit ?

[gilligan]

Didn't have my desoldering iron with me, will pull it next week and see.

I did find a thyrister datasheet when I was googling the part number, guess I want wrong to take a look at that.

Thanks

[gilligan]

Ok, so the MOV is NOT bad, it reads wide open with a DMM.

The SCRs are still shorted with the MOV removed from the circuit.

[gilligan]

Bump