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

Phil Krichbaum vailphil at sopris.net
Tue Dec 16 09:22:55 EST 2008


Julio,
    One of the quick fixes tried was to change the jumper in case it was 
bad and I went thru several of varying lengths. The length I had been 
using had been used for a long time with no problem but as they say s@#$ 
happens! I will test all my jumpers just in case.
    73 Phil N0KE

Julio Peralta wrote:
> 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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