On Wed, 24 Dec 2008 19:58:37 +0000, Joe McElvenney
put finger to keyboard and composed:

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

US patent number 5,512,732 ...

http://www.google.com/patents/pdf/Sw...0K xc1wO6MuFw

.... refers to a "ferrite reed switch" obtained from Therm-O-Disc, Inc
of Mansfield, Ohio, model MTS-90B with a Curie temperature of 90 degC.

US patent number 4,509,029 ...

http://www.google.com/patents/pdf/Th...sZS7rwyBfNBD3Q

.... assigned to Midwest Components, Inc, (MCI?) describes a thermal
switch consisting of "a reed switch surrounded by an annular collar
made of ferrite material and a pair of annular permanent magnets".

The latter patent refers to a brochure entitled "Thermal Reed
Switches" by Tohoku Metal Industries.

I suspect that "MTS" may stand for "Magnetic Temperature Switch".
There are plenty of Google hits for this term.

AFAICT, Midwest Components, Inc is a division of Therm-O-Disc, Inc:
http://www.thermodisc.com/index.asp

This site lists an MTS90B part made by MCI:
http://www.mwcomponents.com/~midwest...ser_part=mts90

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.