Hello Michael,

looks to me it is "M" medium acting fuse...

for the 200W model (654xA and 664xA) 5A

for the 500W model 12A...

- You need 5A Medium acting fuse (without marking; there should be no "F" or "T")

Istvan

2023. 11. 13. 22:31 keltezéssel, Michael Yellin írta:

Hello All,

I recently obtained two HP 6643A units, one working, and the other not working.? I started to troubleshoot the broken one, my first step was checking the Mains fuse, in the service manual known as F450.? When I check the specs in the manual, it conflicts in some places, as well as not providing all the needed information.

First, in two places, it states that the fuse should be a 12amp fuse for 120 Volt operation, while in another place, it indicates a 5amp fuse for 120 volt operation. (See below) The popped fuse I removed was a 5amp fuse.? I then checked the working unit, and it also had a 5 amp fuse.? Last, no where does it mention the physical size of the fuse (I measured it at 32mm by 12mm or 1.25 in by .25 in.) nor does it mention whether it should be fast or slow acting,

Can anyone provide any guidence?

TIA
Michael