Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ulowell!m2c!wpi!markc
From: markc@wpi.wpi.edu (Mark B. Cohen)
Newsgroups: comp.sys.ibm.pc
Subject: System Unit Design
Keywords: Where is the fuse?
Message-ID: <1256@wpi.wpi.edu>
Date: 9 Mar 89 21:20:36 GMT
Organization: Worcester Polytechnic Institute, Worcester, Mass.
Lines: 76

This morning I sat down at my PC to send out a letter, turned the
power switch on and nothing happened.

No beep, no fan, no nothing.

The monitor came on fine - blank of course, but fine.

So I checked the AC outlet - no problem.
The power supply cable was conducting fine too.
My surge protector was also normal.

So...  I look around the back of the system unit for a fuse socket.  Nothing.
I remove the system unit cover, and find the power supply is one single
sealed unit, as expected.  (Naturally, I knew that already, from having
installed boards and drives, but one can dream, right?)  There is, however,
a notice on the power supply, along with the "WARNING - No Servicable
Components Inside" label, another notice:  "WARNING - Be certain to 
replace fuse with exact size and rating or damage may occur" [paraphrased].

At this point I should add that RTFM mentioned nothing about fuses.
["Contact your dealer or technical support" under generic troubleshooting
section - how wonderful.]  

The access screws on the power supply were placed in a way so that the 
supply had to be removed from the system unit to reach them.  Removing
the power supply entailed removing several expansion cards to gain access
to the system board power connectors, as well as removing the disk drives
(two hard, two floppy).  

Now I had a dead power supply by itself.  External inspection showed no
access points:  The only openings were for cables, the switch, and the fan,
plus numerous ventilation points.  Opening the power supply (yes, it had
been off for at least an hour at this point, so the caps were discharged)
involved seven screws (the system unit cover is only held on by six), which
presented me with the reverse side of a circuit board, and a view of
another circuit board.  And lo and behold!  There on the second board
were two fuses, one of them clearly blown.  

To reach this fuses, I had to remove the first circuit board, disconnect
two multi-pin sockets which gave access to an internal divider.
This internal divider was held by three screws, which finally 
allowed me to remove and change the blown fuse.


Anyway... thanks for bearing with me through this saga.  
My question for the net (and the reason for this post) is this:  

	Why would a designer place a disposable/exchangable part
     (such as a fuse) deep inside a 'sealed' assembly that has
     existing external connections?  

        The ^&*% manual gives explicit instructions on how to 
     insert chips on the system board.  Why can't it have a 
     section on how to change a fuse?

Just to kill time while having tried to figure this out, I priced the
cost of a manufacturers replacement power supply.  
It's a Mitsubishi made system, marketed by the late Leading Edge, and
I paid $2500 two and a half years ago for the system with a 30Mb
drive, 1.2Mb floppy, and 1Mb RAM.  The processor is a '286 @ 8MHz.
A replacment power supply (I think it's 135W, it is NOT labelled) 
listed for $431.25, plus shipping, etc.

A more novice user, or someone smart enough [to not try electrocuting
themselves :-) ], might have replaced the entire unit.  I don't 
believe that this is good design either.  

How are other systems designed?  I can't recall ever having seen
any PC with a visible fuse socket - although I'm sure they MUST exist.

Frustrated, but up and running,
Mark
-- 
Internet:  markc@wpi.wpi.edu                         "This is drugs...
UUCP:      {backbone}!husc6!m2c!wpi!markc             this is your brain...
BITnet:    markc@wpi.bitnet                           this is your breakfast."