The disk drive looked awful inside and out and once the loose debris was removed it still looked awful.
The cover was very corroded and the IEEE-488 connector was broken although the pins were intact.
After a wipe over, a blowout, and a first board wash started to look a little better with the board appearing to be less corroded than the computer boards.
There was no rush to get the drive going because I didn’t have a computer to test it with, and I didn’t have a connecting cable. I ordered a short GPIB cable from China and an edge connector locally with a view to modifying the standard cable.
PCB corrosion was treated with soapy vinegar and after two passes the board was quite acceptable. The IC legs were in much better condition than those on the computer boards.
The tin can was treated with deoxit over several days and was then cleaned and painted with zinc paint.
The drive was thoroughly cleaned and lubricated. It had no corrosion and the head carriage moved freely.
The case was processed in much the same way as the computer bases. See above. The corrosion was severe enough that filler was required. I’m at a loss to explain why the case was so corroded but the PCB was good – despite the ventilation slots on the top of the case.
Transformer voltages were checked before power on. I was surprised to find that the drive started with a spin and then gave a solid light as per the manual. This was a good sign.
Alas, smoke followed, which is when I realised that there was probably a Rifa hidden away inside the IEC inlet filter.
Although I had a spare filter, it was too large to fit under the wiring cover, so I have reverted to a simple inlet with no filter. I don’t like doing this, and I will revisit in the future.
I made up the cable by unpicking one of the GPIB connectors and replacing it with an edge connector. The supplier sent the wrong size, so I had to cut it down to suit (2×12 rather than 2×22).
I made up a 2031 demonstration disk using a greaseweazle and a 40 track drive. I had trouble doing this via SCP, but it worked fine writing direct. Initially the drive was unreliable, but after a more exacting cleaning of the head it ran and passed the drive performance test.
Most games were written for 40 columns, so for the 80 column machine to work it has to run in a 40 column compatible mode. This is done by running a program which effects the changes: CBM4032.
The program was easy enough to find, but I had to put it in a disk image. As is often the case, there’s an app for that. I used DirMaster. Then the image just has to be written with greaseweazle.
I found that sometimes the disk drive stopped working. When it did, it is because the head carriage was not moving reliably. My best guess was that there is an intermittent fault in the stepper motor drive circuit. It did not seem to be the connector.
The soldering on the board looks very good.
When the drive worked it worked very well, so the fundamentals seem good.
I used the scope to have a look at the stepper motor drive signals. One was not like the others. The stepper is driven by a quad resistor array FPQ3724. The transistor at pins 12,13,14 did not seem to be presenting a 0.7V drop in operation. On the meter it looked fine. Pin 14 was quite corroded, so perhaps some moisture had got in. It’s also possible that it had just blown – not unusual. An identical array is quite hard to get so in the short term I’ve patched a BC337 transistor in parallel. This seems to have resolved the problem for now.
