Was looking at buying an RGB2HDMI previously, so with the need for a monitor option for this machine, and a guaranteed working monitor to test the IBM 5160 I also want to restore (which is MDA), I took the plunge and ordered one. I also ordered a TTL Buffer board, as I’d rather blow up a buffer board than the RGB2HDMI or a Raspberry Pi Zero. Have also arranged for a Raspberry Pi Zero to use with it from a local friend who has a few on hand. Don’t know if the RGB2HDMI will arrive before the end of the month though. Fingers crossed.
While I wait for an ETA on when it will arrive, I’m moving on to things I can do/solve in the meantime.
First up: The case top is held on with 4x 3mm screws. These were part of the case, but the embedded nut for one of these broke off. These look to be nutsert type rivnuts that were put into the case bottom, then possibly welded into place before painting. Getting hold of something similar here in Canberra might be a bit of a push, plus you usually need a special tool to insert them, so I’ll attempt to reattach it to the case.
Broke out the Permatex Cold Weld Araldite (designed for joining metal to metal) and glued it back in place. Used a nylon screw to hold it in place while it sets. The idea was that if the glue ends up on the screw, I can easily drill it out and remove any remainder from the hole.
Pic of glued embedded nut in side of the case:
This didn’t work as planned though. The join wasn’t as strong as I was hoping, and due to a someone previously trying to put the wrong screw into the case, the thread in the embedded nut was damaged. The nylon screw deformed enough to allow it to pass through the damaged thread, but when I attempted to put a proper steel screw in there, the pressure was too much for the join (which was not as good as I hoped) and the araldite failed.
I used a M3 tap to clean up the threads in the embedded nut. Will also be running the same tap through the other embedded nuts that are used to hold the lid in place as a precaution, as I would not be surprised if the threads are all damaged.
Once tapped, I cleaned up all the araldyte from the embedded nut and the case around the matching hole. Scratched up both surfaces heavily (with a pointed file) to give the glue more purchase. Using a steel screw and nut, pulled the embedded nut into place on the case as hard as I could. This actually made the embedded nut stay in the case without glue, though only loosely. I then Cold Weld araldyted the embedded nut to the case, while holding it with the metal screw/nut done up to keep it in place. I’m confident that the screw does not have any araldite on it, so it shouldn’t present any issues with removal.
Pic of screw and nut hanging from the embedded nut, but before araldite:
Pic of round 2 of using araldite on the embedded nut:
While I was waiting for the first araldyte join to cure, I proceeded to test what chips I can on the RAM/SCSI Expansion and the two Disk Controllers I have.
There were a few chip failures:
- 1x Z80 on one of the Disk Controller boards.
– Fortunately I have 2 of these boards, though the SCSI interface is only populated on one of them. Hopefully between them I can at least get one with SCSI working. - 7x KM44C256-8 RAM chips off the RAM/SCSI Expansion.
– These are 256K by 4 bit wide chips. Lots of brands of these were made and used in a lot of things, but of course, getting hold of them may still be hard and even then you may end up with fakes.
I can’t test the NCR SCSI controller chips (NCR5380), and I’m yet to try ripping any of the PAL chips from the board, which will be next up. If any of the PAL chips are bad on the Disk Controllers, that may halt things.
I did however rip the Roms from the Disk Controllers (V1.4 and V2.2), and they all seem to be fine.
Pic of the boards with the bad chips removed:
I’m probably going to have to shelve the RAM/SCSI Expansion card for the moment and concentrate on one of the Disk Controllers. The SCSI access will be slow, but that is better than not working at all.
Reading the docs for the RAM/SCSI Expansion, it seems you need to load a driver off disk to be able to use the SCSI on that card. The main way they suggest you do this is to use the SCSI on the Disk Controller card to load the driver off the hard disk, then use the RAM/SCSI card for any remaining accesses. This means there’s 2 SCSI masters on the bus, both talking to the same drive. I asked one of the developers on the BlueSCSI Discord and they seem to think it should work fine with the BlueSCSI. Of course, the other alternative is to load the driver off floppy. I’ve got a Gotek floppy emulator that I could (in theory) load the drivers on, which would be more stable over time than using an actual floppy disk.
Thinking ahead to the next things to do:
- There are a lot of holes in the back of the case, and they were how most of the dust got into the machine. Most likely, I will laser-cut some matching acrylic plates with the laser cutter at the Canberra Makerspace (aka Make Hack Void) to fill most of these holes. I’m also thinking I will put in an 80mm fan, since there is a suitable cut-out for one on the back of the case.
- There are also holes in the bottom at the front for what most likely would be for a hard drive, either with brackets or directly screwing to the case. I might laser-cut some brackets or adapter plates for these as well, depending on what seems to be required.