Hi,
Strapped directly across the b-e junction of a TIPL755A bipolar in a SMPS out of a HP54502A scope is the following -
Body - cylindrical, black plastic, 5/8" long by 1/4" dia.
Body markings - MCS MTS 90A.
Leads - two, axial.
PCB marking - S1.
Polarity markings - nil.
Condition - s/c.
Naturally I don't have a schematic but my guess is that it's some sort of over-voltage clamp. A great deal of googling hasn't helped me so any info would be much appreciated.
Happy Holidays - Joe
Hi,
Apologies the markings should read - MCI (not MCS) MTI 90A.
Cheers - Joe
inductor ?
It doesn't appear to have the schematic but the 'service' manual is available for free at the manufacturer's website:
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On Mon, 22 Dec 2008 13:35:11 +0000, Joe McElvenney put finger to keyboard and composed:
Is there an S2?
I don't know what a coil would be doing across a B-E junction, but can you measure any inductance?
I can't imagine that S1 is an OV clamp, unless it is a reverse biased diode for protection against excessive negative voltages. But then a diode would have a polarity marking.
Does the body of the device have sharp ends (like a 1N4007 diode) or are the ends rounded like a resistor?
- Franc Zabkar
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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
On Wed, 24 Dec 2008 19:58:37 +0000, Joe McElvenney put finger to keyboard and composed:
US patent number 5,512,732 ...
... 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 ...
... 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:
This site lists an MTS90B part made by MCI:
- Franc Zabkar
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