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

[Julio Peralta]

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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>
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