[Milsurplus] Warning - PRC-117 battery box problem
ross at hypertools.com
Sun Apr 18 20:01:32 EDT 2010
I have a Harris PRC-117 (plain, with no letter) with the attached
battery box. I generally use a BA-5590 lithium battery to run the
radio. I was fussing around with the radio yesterday - I had the
battery box off the radio and was powering the radio from a small bench
As I sat the radio on the battery box and began to clamp the box back
on the radio, I saw sparks from the radio case to the battery box. The
radio was turned off at the time - the radio was OK but both internal
fuses in the BA-5590 were blown.
The battery box contains a 20CTQ030 made by International Rectifier, it
is a pair of diodes in a TO-220 three-pin package and is used to isolate
the two batteries inside the BA-5590 package. The mounting pad on the
20CTQ030 is hot, it sits at about +14.5 Volts and must be isolated from
the battery box chassis.
My battery box had no insulator between the 20CTQ030 and the chassis -
no mica washer and no silicone pad. There was a lot of white thermal
grease under the diode pack. This battery box had worked for nearly 20
years with only thermal grease and a thin layer of anodized aluminum as
electrical insulators between the aluminum chassis and the TO-220 diode
Well OK, maybe this was a single failure, maybe someone was asleep on
the assembly line when they assembled my battery box. I emailed a buddy
who has a pair of PRC-117s & battery boxes - yep he has had the same
problem - the insulator was missing in one of his battery boxes too.
So if you have a PRC-117 & battery box, it might pay you to take a look
inside the battery box and check for this particular problem.
Incidentally, the PRC-117 works fine as the 'second radio' when
connected to a PRC-343. Ditto the PRC-68B, but it is possible to wake
up the FILL function in the PRC-68B if you release the second PTT switch
and then actuate it again too soon (like less than a second later).
Dave Ross N7EPI
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