Troubleshooting an IBM 5155 - (portable personal computer)

[Tony Duell]

> 
> OK, for a little on topic. Before I go tearing the whole machine apart.....

Actually, they're not that difficult to work on.... I've had one 
_totally_ apart (including the PSU and monitor sections) and I've done a 
lot worse.

> 
> I am the proud new owner of a nice example of the IBM 5155. This thing is in
> pretty good shape. Turned it on, A: did a quick seek and the I was into
> BASIC. So far, so good. Now, I'm trying to boot DOS. I have several known
> good DOS 3.1 boot floppies on 360K disks. I keep an old 486 with a 360K
> drive just for this (and for creating disks for my Tandy model 4). 
> 
> Anyway, the original A: drive only gives a "boot failure". The B: drive
> (after a cable swap) boots sometimes. Taking out these drives looks to be a
> MAJOR undertaking. Not along the lines of multiple years, but they are

I assume you've got the case off, and the upper shield over the logic 
boards (if it's present, it wasn't fitted in all machines). 

To get the drives out, you take out all the expansion cards behind them, 
and unplug the cables. On the right side, you remove the metal bracket 
that supported the back end of the drives and loosen the front mounting 
screw. On the left side, AFAIR, there's only one screw which, again, you 
loosen. You can get a 3/16" AF spannee in there, I think even a small 
socket and right-angled bar will go in. The drive then slides out 
backwards. You have to remove the top drive before the bottom one (and 
put the bottom one back in first.

> pretty securly installed. However, I'd like to keep them because they have
> the IBM faceplate.
> 
>  Now, for the questions...
> 
> Are these Qume drives subject to any known failure? Should I just dig in,
> remove these drives and give them a good cleaning and lubricating? I'm used

Certainly clean them. A trace of lubricant on the head slide rails can't 
hurt, but only a trace. You might want to dismantle the spindle assembly 
to lubricate its bearings too. I forget exactly how to do this (and while 
I have a scheamtic of these drives in the IBM O&A TechRef, I don't have 
the Qume service manual), but normally the rotor comes off the bottom 
either by 3 screws holding it to the hub or by a central screw which may 
well be _left handed_!

> to working with the big 8" drives, where everything is a bit larger. What is
> the best way to clean the heads? Lint free swab and 90% Isopropyl alchohol?
> Cleaning disk? Nail file ;-) What's the consensus?

Cotton bud (or swap) and pure isopropyl alcohol (propan-2-ol). 

> 
> Any suggestions or comments in general about this machine?

It's a PC/XT at heart. The motherboard is the IBM PC/XT board, and it'll 
therefroe take the 640K mod (which I am sure is well-known). The video 
card is the nromal CGA card, the floppy controller is also normal. Any 
other I/O cards are optional, but if they're IBM ones, they're the 
standard IBM ones. 

The PSU is similar to the PC/XT PSU, but not identical. Mine looks to 
have been made by Zenith. The monitor has a sompositie video input which 
is connected to the 4 pin header on the CGA card that was originally 
intended for an RF modulator. 

The keyboard also seems to be the PC/XT one, in a different case. 

Anything else you need to know? I have the IBM Techrefs covering this 
machine, so I've got full schematics, etc.

-tony