FW: [BC] Harris SX-1 Spur Problem

[radioranger]

<<There are some of us old guys who still know that transmitter.  Let us
know 
if you find anything or need some more suggestions.

Best regards,
Dan Dickey>>

Well, I've asked the question before Dan, but you're a new player in the
game of SX transmitter questions!  The SX-5 I deal with blows fuses.  There
are two fuses in series between the PDM amps and the PDM filter board--- one
is mounted on the pull up board and is a 3AG 4 amp fuse, and the other is a
10 amp KTK cartridge fuse, mounted in a holder on the front or back of the
side panel.  The 10 amp fuses blow, but rarely the 4 amp fuses that are in
series with the 10 amp fuse.  The PDM output levels are all real close to
each other, and we've checked all the other operating parameters and talked
with Harris Field Service, to no avail.  The fuses that blow are always
different--- sometimes on one PDM board, sometimes on another.  If you shut
down the transmitter and feel the 10 amp fuse holders some will be warmer
than others--- sometimes almost too hot to touch.  Replacing the fuse cures
the problem for a month or so, until another 10 amp fuse blows.  I wondered
if the problem wasn't just heat that melted the fuse element so I rigged a
muffin fan inside the back door over the power transformer to blow more air
on the holders mounted in back, and none of those have blown so far. 
So, why are there two fuses in series, and what's going on?  All other
operating parameters of the transmitter, including the output as viewed on a
spectrum analyzer, look OK.  All power supply caps are new.



Steve Brown
Radio Rangers
Minneapolis