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

[Frank Haas KB4T]

About annually, my IC-756ProII operated off a PS-125 would begin
shutting down instantly upon an attempt to transmit. I found that the
power lugs inside the rig screwed to a circuit board on the top side
of the chassis would develop some sort of corrosion. I found I could
unscrew both the positive and negative lugs and tighten them down
again and the problem vanished for another year. 

As a two way tech I find that many cheap, poor quality fuseholders
will loosen over time and develop a relatively high resistance in
series with the 12 volt power lead. Under high current demand
conditions (20 to 25 amps) especially when there is a sustained key
down situation, the resistance would create enough heat to unsolder or
loosen the fuse element inside the equally cheap poor quality fuse.
Cleaning the fuseholder internals solved the problem on a temporary
basis. Replacing the fuseholder with a substantial, high quality
fuseholder was the best solution. 

A good quality fuseholder which must pass high current on a sustained
basis should use a large surface contact on each end of the fuse.
Motorola 30 amp fuseholders employed large 3/8 inch diameter 30 amp
fuses with equally massive end contacts inside the fuseholder. Other
high current fuseholders use contacts that surround the entire
circular end contact of the fuse to insure a solid mechanical low
resistance connection capable of coping with high current flow without
heating up. 

The major ham rig manufacturers don't supply such stout fuseholders.
Instead the fuseholders provided with most HF rigs are somewhat less
substantial and prone to overheating issues. Where I encounter
overheating and intermittent operation, I replace the low end
fuseholder with something much more substantial and end the problem
entirely. 

My ProIII has not exhibited the same occasional intermittent power
reset problem that my ProII has. Perhaps the materials used for the
internal power connections were improved in the ProIII. 

Hope this helps. 73 & Happy Holidays!

Frank N. Haas KB4T