[ICOM] 781 TR/REG Problem

Mike Wetzel mjwetzel at comcast.net
Sat Dec 20 00:33:19 EST 2008


My 781 first blew a fuse then blew R20 then the transistors on the TR board
all shorted.  After I replaced the TR board, I thought I had the problem
fixed because the radio worked for about a week (scope bottom line was 3
divisions higher then before-I did adjust voltages)  but then it blew the
fuse again and the TR board transistors are shorted again.  When the TR
board transistor short there are burned holes in the disc caps on that
board.  This happened at turn on.   The replacement board was from a parts
781.

 

I sent the unit off to Icom for repair  but:

 

I just got a call from Icom and the guy (who is an outside contractor for
Icom but works exclusively on 781's) says that he has replaced the
transistors on the TR board several times, replaced several other components
(regs, IC's and caps)  but says it keeps blowing fuses and shorting the
transistors on that TR board.  He guesses that replacing the REG board would
be next but he says none are available so he says he cannot fix the radio!
He said the start up circuit seems ok.  I offered my spare REG board but he
said the chances of it working were slim since it is from a lightning
damaged radio.

 

Has anyone had this problem and can anyone offer any suggestions?

 

Thanks,

 

Mike W9RE

 



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