Troubleshooting an IBM 5155 - (portable personal computer)

[Tony Duell]

['scope]
> I'll see if anyone in the local radio club has any I could borrow for a few
> evenings. I know how to use one, it's just been a few years. I have an old
> Heathkit scope behind me, but there's another thing waiting for my
> attention. The trace is about as wide as my pinky and as noisy as heck. Not
> real helpful I'm afraid.

Ah yes... Some Heathkits are prone to that. It's either a changed 
resistor in the EHT divider chain, an internal leak in the CRT, or a leak 
in the mains transformer (I've come across all 3 faults...) You pray it's 
the first one, of course.

[...]

> What is the general opinion on adding an HD to this machine (if it will even
> work)? I've got plenty of ST-406/ST-512 interface drives and controllers for
> 8 bit machines. Of course I only want this for show and tell, so it is not a
> requirement.

IBM never supported a hard drive in this machine, but that doesn't mean 
it won't work. As it's a stock XT motherboard with the standard BIOS, 
electronically (and with the firmware) there's no problem. The only 
problem is getting it all to fit.

IO bought my 5155 (second-hand, of course) with a half-height 5.25" 
Winchester in one of the drive bays, cableed to a half-length controller 
card in one of the slots. It worked fine, but as I wanted to make the 
machine as near original as possible, I removed it, and fitted a real 
'IBM' Qume floppy drive. That hard drive has now been recycled (don't 
panic, I mean it's gone into some other machine, probably not even a PC, 
that neede an ST506 drive). 

Another option that certainly works is to use the IBM 5161 expansion 
cabinet. You have to put the extended board in slot 2 of the 5155, since 
that's the only one it will physcially fit in. You then put a hard disk 
controller in the expansio unit, and hae 2 full-height bays for the 
drives. The only problem is finding a complete 5161 with the extender 
card and the cable.

I suppose (although I have never tried it) that a hardcard would go in 
slot 2 also.

-tony