Subject: TOHM power supplies fixed
Ioanni.Katsavounidis@lngs.infn.it
Date: Thu Nov 11 1999 - 09:18:44 EST
Ciao a tutti,
As we all know, yesterday, following MACRO's shutdown/power-on, there
were 2 broken Kinetic Systems (TOHM) CAMAC power supplies.
The first one that came from SM4 (Model 1500) and the second that
came from SM2 (Model 1502). They both had broken pass transistors on
the -12V line.
Model 1500 could provide up to 3A on the -12V line but
failed (went into current foldback limiting) when asking for 4A.
In fact, simple DVM measures don't reveal anything wrong with the
corresponding 2N3771 transistor. Yet, by changing this transistor,
the power supply can now supply all 4A with no problems (tested it
for a short pieriod).
Model 1502 wouldn't even turn on: -12V went in protection mode
immediately. The corresponding 2N6050 pass transistor was actually
measuring 1Ohm between collector and emitter (...) After changing
it, it tested OK with full load.
Our third such spare (a model 1500) has also been tested OK under
full load. I remind you that this one has occasianaly failed on
the test crate; I believe this was due to transients.
A presto,
Ioannis
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