[Milsurplus] Warning - PRC-117 battery box problem

[David Ross]

 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 
power supply.

 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 
pack.

 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