Cii Honeywell Bull TTX 90

I purchased this computer locally as untested, together with the Sharp MX-80B. It came with a whole collection of 8" floppies, but unfortunately those all turned out to be data disks and disks for other machines.

From the little information I have been able to find about this machine online, it appears to be a rebadged CPT 8525 word processor. It's based on a 8080 processor and likely has 96K of memory installed and uses two 8" floppy drives for storage. Aside from being a dedicated word processor, it presumably can also run CP/M, but I haven't been able to find any media for this.

At this point I've been unable to get it to fully boot, I'm not even certain if I've found the correct software for it, although likely it has one or more faults as well.

Work done:
Planned work:

Exterior inspection:

The machine was in reasonable shape for it's age:

Front

Front bottom

Side

Back ports

Side options

Interior inspection:

After removing the front cover, the overall design is revealed. The computer is separate into 3 distinct sections; on the left a monitor, on the right is the computer itself: Front opened

Back monitor

Side monitor

Inside I found several notes with previous repairs: Repair notes 1

Each of these sections can be removed separately, which reveals that the whole base of the computer is taken up by the power supply and fan:

PSU open

Computer cards:

The computer itself is based on 4 cards connected through a backplane and a ribbon cable. There is a space for a fith card, but none was installed:

The first appears to be the floppy and I/O controller: Floppy controller top

Floppy controller bottom

The second is the CPU board, showing a National Semiconductor N8080 CPU: CPU board top

CPU board bottom

The third appears to be the video controller, which is directly connected to the memory board through a ribbon cable: Video board top

Video board bottom

Lastly is the RAM board, from the layout I assume it has 96K of RAM installed, 6 columns of 9 ICs (8 bits + 1 parity). With a maximum of 128K when all ICs are populated. The memory ICs are 16K 4116's made by MOSTEK, which are unfortunately not very well known for their reliability... RAM board top

RAM board bottom

RIFA replacements and first power on

The first step was to check for any RIFA capacitors, which tend to blow up and leave a very nasty smell. I found a record number of 10 RIFA's in this power supply, in many more verities than I had replacements for, so I first had to order those: RIFAs removed

After this, it was time for the first power on:

Bad image

After a few seconds the image started to flicker and a lot of smoke came from the card cage.

Tantalum replacement and first signs of life

After a quick investigation, I found that one of the tantalum capacitors had shorted:

Blown tantalum

Since these are usually not strictly required, I decided to cut it off and power it on again. The same image came up again and a few seconds later more smoke emerged from the computer cage.

At this point I decided to just remove all the tantalums from the floppy board and try again, and this is when I saw the first signs of life!

First signs of life

After this I replaced all 4 tantalums on this board

Floppy drive

Now it was time to clean up the floppy drives, so I could try booting some software: Floppy top

Floppy bottom

Floppy board removed

Floppy board bottom

Floppy back

Finding software

Initially I had assumed that there would be a program disk together with the 8" floppies, but unfortunately this was not the case, so I had to find a program disk image somewhere on the internet, which turned out to be more difficult than expected.

I ended up finding a link a FTP server of the University of Stuttgart on this website. The FTP server is part of the university's Computermuseum der Informatik.

There I was able to find a disk image for the CPT 8515 Program Disk. Using another 8" Floppy drive and a Greaseweazle I was able to write the disk.

I booted up the machine, inserted the disk and crossed my fingers..., but unfortunately it still wouldn't boot. It was definitely getting further, because previously when I had inserted any other disk, it would just seek between presumably track 1 and 2 every second or so. But now it was actually seeking all over the disk.

Unfortunately, it ended up with a E1 error on the screen:

Error

I made a few more attempts, including having the keyboard connected, but I started to sometimes get a red LED on the CPU board. After a few more attempts, I now only get the red LED on no more text on the screen when inserting the floppy.

Further troubleshooting

Unfortunately, I don't have any schematics for this machine and the cards are inaccessible inside the cage, which will make troubleshooting a lot harder. I also still don't even know if I have the correct floppy, it's entirely possible that Cii Honeywell Bull used a different ROM from the CPT 8815, or that it's based on a different model all together. I did do one more attempt to write the floppy using the computer's own floppy drive, but this didn't make any difference.

Right now, I'm planning to design an extender card for the computer, so I can test the cards outside the computer and attach my logic analyser.

Another option is to attempt to power the memory board separately from the computer and use a tester on each IC, like I did for the Wang PC

The three most likely issues I forsee are: