Hi everybody,

It appears that the components is a thermal switch that shunts base
current away from the switching transistor when the ambient board
temperature reaches a certain figure due to a fault condition such as
an overload or a fan failure.

I have the HP service manual but it doesn't have a parts list or
schematic for the SMPS, so I'm reduced to guessing my way round the
circuit. The unit works without the temperature switch but I can use a
locally available substitute while looking for the real thing. I am
currently investigating a source of C122F1 SCR's so I may fix the
+5.2V regulator.

BTW, I gave the marking incorrectly - twice; they are MCI MTS 90A.


Thanks for your help - Joe