Littelfuse age fatigue/failure(Bird 4421 RF meter repair)?

[TheSteve]

I recently purchased a Bird 4421 electronic RF watt/SWR meter with a 4022(25 to 1000 MHz 1 KW) sampler head. The 4421 powered up fine but indicated it could not communicate with the sampler head. I opened things up and found two 2 amp fuses going to the head, one was blown. I did the simple fix and replaced the blown fuse(with the proper value). I then gave it another try and the second fuse blew. At this point I figured I had better investigate instead of just swapping another fuse. I couldn't find anything that seemed like a problem. I eventually connected the sampler head up to an Agilent supply set to 15 volts and 0.2 amps max. There was no drama and the head drew a reasonable 50 mAh. Not able to find a problem with anything including the cable that connects the two units I replaced the second fuse and powered it up. It has been working fine ever since. I have wiggled cables and moved things around with no issues.

So that said, has anyone seen an age related failure to a Littelfuse style fuse? The fuse is the standard green one that is the same size as a normal 1/4 watt through-hole resistor. The unit was built in the 80's so they were likely 30 years old.

Pics of the unit measuring a radio with a rated 50 watt output(all looks good!) and of course a blown fuse attached.

[mojoe]

My guess is that the sensor got abused in the past, which blew the one fuse. This probably stressed the other fuse, also. Those look like polyfuses to me.

[PA0PBZ]

+1

I guess the old second fuse got a good beating when the first one blew, and you just ended his misery.