[ICOM] IC 756 Pro III fuse over-heating?

Tue Dec 16 09:40:05 EST 2008

There is some merit to the length of the coax.

Years ago I had a Collins KWM-1 and there was a note that recommended a 21
ft length of coax between the KWM-1 and the 30L-1 linear. I don't know the
theory on how they arrived at the 21ft. But it does make some sense. I just
coil the excess up behind the desk and it makes a good RF choke between my
FT-920/IC-735 and the Clipperton-L.amp.

   * 73's Jim W5IFP *

   >-----Original Message-----
   >From: icom-bounces at mailman.qth.net
   >[mailto:icom-bounces at mailman.qth.net]On Behalf Of Julio Peralta
   >Sent: Tuesday, December 16, 2008 1:02 PM
   >To: 'ICOM Reflector'
   >Subject: RE: [ICOM] IC 756 Pro III fuse over-heating?
   >
   >
   >Try changing the length of the coax between the rig and the input to the
   >amp. Sometimes the length of that cable will cause the rig to
   >reduce power
   >out until it determines the match is OK. I've experienced this myself.
   >
   >Julio, W4HY
   >
   >-----Original Message-----
   >From: icom-bounces at mailman.qth.net
   >[mailto:icom-bounces at mailman.qth.net] On
   >Behalf Of Phil Krichbaum
   >Sent: Tuesday, December 16, 2008 5:49 AM
   >To: ICOM Reflector
   >Subject: Re: [ICOM] IC 756 Pro III fuse over-heating?
   >
   >    On Saturday night I had been running along working a bit on 10m CW
   >and then got a phone call. When I came back on the air some 15 minutes
   >later the Alpha 91B grid safety feature would trip after about two
   >seconds. I'd not had this problem previously in this contest
   >during some
   >good runs or ever before. I have two antennas and one is about
   >1.3:1 and
   >the other 1:1 and it didn't mater which antenna I used. I was running
   >the 756PROIII at less than 50w output. A little further checking  and I
   >noticed when I first started to transmit I was getting less than QRP
   >output for 2-3 seconds before going to the set power level. This in
   >itself is a very undesirable feature for contesting not to mention not
   >having the amp available as it would trip as the power came up!  Just
   >for the heck of it I tried loading on 20m and everything seemed OK. I
   >went back to 10m and same problem. I bypassed the Alpha and same
   >problem. I tried a different amp, same problem! I removed the
   >PROIII and
   >no problem with another rig and finished the rest of the
   >contest with it.
   >    I'm using the Icom PS125 that came with my PROII "free" as a
   >closeout sales promotion (I certainly would not pay that much
   >for a 25 A
   >switcher). The PROII got taken out of service permanently with a
   >lightening surge that apparently came in the neutral side of the power
   >line. My PROII was off but this PS125 was left on (I've changed that
   >practice with the PROIII). I assume the PS125 means it is rated at 25
   >amps and there is a short power cord of about 12 inches with no fuses
   >and the 6 connector Jones type plug on the end. I suspect if there are
   >fuses, they are inside the PS125. I need to do some further checking of
   >the problem as to what bands are affected and at what power levels. A
   >friend had a similar problem on 6m last summer and it eventually went
   >way by itself. It seems I should try a different PS if the problem
   >persists and also take a look at the fuses in the PS125. Perhaps the
   >PS125 was damaged somehow when the surge came thru it. Damage
   >to the rig
   >also came in the rig control cable and CW keying jack from my desktop
   >that was connected but off. The HD in the desktop was toast. I
   >have also
   >picked up some 3 wire 250V 30A knife switches they use in Costa Rica at
   >the main house feed to shut off power to the house and will
   >install then
   >on my 120 and 240 lines into the shack prior to spring so there will be
   >no connection to the house wiring when I leave the shack assuming I
   >remember to throw the switch! I've also had my power provider install a
   >"Meter Treater" at my meter which has some big  MOVs in it.
   >    Anyways it seems like I need to check the PROIII with a
   >different PS
   >if this problem doesn't fix itself!
   >    73 Phil N0KE
   >
   >Jim Reisert AD1C wrote:
   >> I've had problems the last couple of weeks with my IC756 Pro III
   >> shutting down in the middle of transmitting.  This weekend I traced it
   >> to the fuses (which were getting warm to the touch).  I  notice that
   >> my SS-30 power supply reports ~ 20 amps being drawn on transmit, and
   >> the fuses are rated at 20 amps.
   >>
   >> **  Is 20 amp draw during full-power transmit normal?
   >>
   >> **  Are the fuses supposed to be 20A?
   >>
   >> **  Should I replace with 25A fuses, or 20A slow-blow, or is there a
   >> bigger problem here?
   >>
   >> Thanks & 73 - Jim AD1C
   >>
   >>
   >>
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   >12/15/2008 5:04 PM
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   >>
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   >
   >----
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