Do SCRs go intermittent?

I doubt it. Anything's possible but once inside the actual SCR, I think if one of the tiny traces breaks, it won't come back to life.

But since it's a heater, it likely draws a lot of current, and that stresses things. The Mac Plus was notorious for a bad connection to the horizontal deflection coil; I got mine when someone didn't want to spend the money to replace the board, I just jumpered around the connector (that was showing signs of burning).

So look at the connections around the SCRs, mayb even reheat the solder to be sure.

Michael

a bad solder joint or a broken wirebond inside the package could do that.

the fan turns very slow or stops. Is it possible for one SCR to be intermit tent?

Bad solder connections are far more common than intermittent semiconductors .

On Mon, 13 Jan 2014 18:31:41 -0800 (PST) in sci.electronics.basics, Bill Bowden wrote,

Much more likely for a connection, like to a SCR lead, to be intermittent.

It sure it however, you could have a sagging line on one half of the sine.. something else using half wave rectification... just a thought..

Jamie

It could also be a triggering problem.