On Mon, 22 Dec 2008 13:35:11 +0000, Joe McElvenney
put finger to keyboard and composed:

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

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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