Capacitors and thyristors, testing replacenemnts... transtig

[graffian]

Or replacements.

The snubber, and all suppresion, caps on my transtig look bad, cases are cracked and open.
Do I bother testing or just replace?

How to test thyristors?

The snubber caps are rifa PMR2026, I can't seem to find .5UF 22R.
what properties, apart from volts, capacitance and resistance should I look
for in non original replacements?

 

[xmetal]

If they are cracked and open then I would replace them. A 470nF, 47ohm RC cap is the nearest I've found by doing a quick search. The older ones are a paper construction internally and absorb the moisture and then they can arc across. Those old rifa ones are notorious for cracking. They also make a mess when they blow.

This guide may be useful for thyristor (SCR) testing.

This one shows another testing method for a thyristor (SCR) but wrongly calls it a triac. The symbol in the circuit diagram is a thyristor, not a triac. A triac is normally used for AC.

 

[Jim Davey]

Or replacements.

The snubber, and all suppresion, caps on my transtig look bad, cases are cracked and open.
Do I bother testing or just replace?

How to test thyristors?

The snubber caps are rifa PMR2026, I can't seem to find .5UF 22R.
what properties, apart from volts, capacitance and resistance should I look
for in non original replacements?

I often go for a higher voltage rating on replacement caps, helps if they are working within themselves.
The thyristors are harder to check, you will need to identify the gate, drain and source and test accordingly, do you have a picture of the item in question? Some tests performed with a multimeter can be misleading as the voltages and currents from the meter are too low to test them properly and a load and voltage must be applied to give accurate readings on good/bad components.

 

[xmetal]

Some tests performed with a multimeter can be misleading as the voltages and currents from the meter are too low to test them properly and a load and voltage must be applied to give accurate readings on good/bad components.

Very true.