Indeed there isn't. Anybody who stares long
enough at the 'No User
Servicible Parts Inside' labeling on an IBM XT power supply, then makes
the effort to find the right tool to open it up and finds the socketed
3AG fuse inside will know just a little bit more about IBM.
Well, I went further than that. I took the PSU apart, took out the PCBs,
and traced out the schematics (along with schematics of the other
'misisng' bits from the Techrefs, the PC/XT/AT supplies, the CGA monitor
supply, the EGA monitor, etc).
The Portable PSU is clearly a Zenith design, and is very similar to the
130W XT supply.
Now, as to that fuse. If it fails, there is a good reason for it.
Probably a shorted semiconductor on the mains side of the supply. It is
very unlikely that just replacing the fuse will do anything except blow
another fuse. And the average user, alas, when he finds a machine that
blows fuses will then put in the highest-rated fuse he can find, and
probably do a lot more damage. There are good reasons, IMHO, to put SMPSU
primary-side fuses away from normal users :-)
Of course if the user is me, then that label is total nonsense anyway. I
will hapilly replace chopper transsitors, etc...
Or is it? When I'm working on the machine, it's broken, and therefore I
can't be using it. So I am not a user :-)
-tony