Triac testing and replacement for a washing machine

[ebourg]

Hi,

I'm trying to repair an old Thomson Australe 2 washing machine that turns on but the programs don't start. The troubleshooting guide has a procedure to display the last error detected by the controller, and it points to a shorted triac driving the motor.

The board looks good, with no burned or cracked component. The triac is mounted on a heatsink, it's a ST BTB15 600BCE. I've tested it in circuit and there is 52mV drop and 42 Ohm between A1 and G. A1-A2 and A2-G are open, with a > 1M Ohm resistance.

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Is this enough to confirm that the triac is indeed bad?

I searched on the ST site and this reference no longer exists, there is a datasheet archived but it doesn't mention the BCE variant. The closest match seems to be the BTB16 which is rated for 16A instead of 15A. However for 600V there are several variants (SWRG, CWRG, BWRG, BRG, CRG) and I don't know which one to pick (if that matters in this case).

[m k]

Replace with one with higher values is a normal route, except sensitivity of course.
Same series usually have others.

Problem appears when next one is mechanically too big.

[Ian.M]

The board looks good, with no burned or cracked component. The triac is mounted on a heatsink, it's a ST BTB15 600BCE. I've tested it in circuit and there is 52mV drop and 42 Ohm between A1 and G. A1-A2 and A2-G are open, with a > 1M Ohm resistance.

Is this enough to confirm that the triac is indeed bad?

On the contrary, those readings indicate the TRIAC is probably good.  If it was bad it would either be blown open, typically with highly visible damage, or shorted A1-A2.

Look elsewhere for the fault.  If you cant find one, we can talk you through testing the TRIAC out of circuit. . .

[floobydust]

I've found a few triacs do have an internal resistor from Gate-MT1, around 50-100 ohms (I think it's for a better dV/dt spec).
The resistance is not shown on the datasheet and my surprise when the new part reads that, same as the old part.

Are you sure this switches the main motor? There are relays on the control board pics that I can see, I would suspect them.

[ebourg]

Thank you, I'll leave that triac alone then I've probably misinterpreted the diagnostic, I'm leaning toward a failure of the door lock which must be locked before the motor starts.

[modoran]

Usually triacs are used for the heater in washing machines and 2 relays for the motor, one for each direction.  Of couse, this is not always the case.