Last time I posted, I mentioned that the VZ200 wasn’t quite right. It seemed logical to tackle it as my next packet of work. The system was sort of working, and after some mucking around I realised that some games were working.
First some background here. The VZ200 has a very limited amount of RAM. In fact, it really only has 6k of scratch RAM. (It also has 2k of graphics RAM, but that’s not really available to me here)
I noticed that the games that worked were all under 4k. Games that were larger than 4k would either corrupt on loading or just corrupt when they were run.
Games under 4k would run fine.
This got me thinking. If games over 4k are crashing, then the last 2k of RAM must be bad.
Looking at the schematics, U4 was the third RAM chip, and I was able to determine (By tracing pins) that the furthest chip from the connector on the RAM mezzanine was U4.
I ordered some replacement 6116 SRAM chips, but remembered I had a Microbee core board with a load of chips on it, that was left over from one of my upgrades. Did this possibly have 6116 RAM on it?
I whipped out the desoldering station and carefully removed one of the SRAM and moved it over to the VZ200 mezzanine board.
(Normally I would socket a chip like this, but there’s no room between the mezzanine board and the main board in the VZ200.)
Booting it up and… It worked! Wahoo!
Every game I tried worked, including expanded ones designed to use the ram in my Benn Venn expansion.
Next up for the VZ200 is to modify the Benn Venn cartridge to add Joystick support. This should be as simple as buying some joystick extension cables and chopping them down to size and soldering them in.
Cleaning the “Battleship” keyboard
While the Battleship was all working, it was still pretty filthy, and had a disturbing rattle, like something like sticks or bug shells floating around inside.
They key caps were also slightly oily, which was unpleasant.
Popping all the keycaps off, I soaked them in warm water with a little dishwasher liquid and most of the grime came off. The water also turned a really disturbing grey.
Wanting to try a trick I had seen, I then added a denture tablet to the water (It promptly turned a sickly green / grey) and left it for a few hours. This did a really good job of cleaning all the caps. A small handful needed an additional wipedown, but not many.
Moving back to the keyboard, I cleaned between as many of the keystems as I could, but I knew I had to bite the bullet and disassemble the keyboard. This proved problematic.
See, there are 3 screws holding the keyboard together. All three have hexagonal heads with a socket size of 7/32″, and no other surfaces to grip to. They’re also recessed in a narrow hole
Let’s let that sink in shall we?
Rare sized bit? Check. Narrow hole? Check. No alternative to a socket? Check.
While I had exactly one 7/32″ socket, it was too wide to get deep into the keyboard. Finding a suitable socket was becoming a fool’s errand. They didn’t seem to be available at anything approaching a reasonable price.
Talking to my dad, he suggested “faking” a tool of some sort, and in desperation, I went through my scraps draw, and found a potential candidate for hacking into a tool.
It was a piece of iron that had come from a cheap plastic ratchet clamp. The plastic had shattered but I figured the piece of iron was a useful size and shape for something in the future, Now was it’s chance to shine.
30 minutes with a hacksaw and a file later, I had added a notch on one end that was pretty close to 7/32″ and narrowed it down on both sides. I had taken advantage of a pre-drilled hole to save me more material removal.
Amazingly this worked first go, and has been used several times since. When it began to slip, I just “tightened” it by tapping the prongs with a hammer.
Opening up the keyboard at last allowed me to remove a lot of dust from the inside, as well as a lot of oily grime from the bed underneath the keystems.
I was also able to find what had been rattling around. Paper punch “holes”. Dozens of them.Obviously someone had opened their paper punch without checking first and spilled the dots through the keyboard.
I also removed the front and back plastics and gave them a good scrub with some surface cleaner.
Once everything was dry, I reattached the front and back, and stuck all the key caps back on.
I also used this as an opportunity to fix the space bar. One of the clips the stabiliser clipped into had weakened, allowing the bar to pop loose. I fixed it with some baking soda and superglue. Thankfully the original clip was still attached.
It all went back together and looks great!
I’ve wanted an upgrade for my TI99/4A for a while, and one of the most popular is the TIPI. The TIPI is, essentially, an interface between a Raspberry Pi and the TI99/4A side expansion port. It can emulate, in various ways, a range of cool hardware that would otherwise plug into the side, such as storage devices, serial ports and the like.
Now, I had looked at these and noticed that avery clever fellow had combined the TIPI with a 32K RAM expansion (That I also needed) and put them all on a teeny tiny board called the TIPI/32k. Better yet, he’d designed it to have all the SMD stuff automatically soldered on by a PCB house. This is very similar to the BlueSCSI.
I found a couple of locals (Hi Ben! Hi Steve!) who also wanted one and ordered a batch of pre-populated boards from JLCPCB. I also placed an order for edge connectors and RAM chips from Mouser and then I sat back and waited for everything to arrive… which it eventually did.
After that it was a case of carefully bending the legs on the connectors, and soldering in a bunch of headers. Everything else was prepopulated.
Once I had them all together, I followed the instructions on programming the CPLD, using a Pi 3 I had lying around. Thankfully, once I realised all the software was on the TIPI boot images, this was a quick and easy process.
After this I had to wait for a Raspberry Pi Zero W to arrive, as I had forgotten to order one ahead of time, and the one I had on hand had the wrong headers on it. (They needed to be on the other side of the Pi to the ones I had already populated for my BBC Master Tube Port)
Once they finally arrived, I whisked it all home and feverishly assembled everything. Amazingly it worked first time.
I am still to explore the limits of what the TIPI/32k can do, but it’s been fun so far.
My next job is to hack in a Jiffy box as a cover while I try and see if I can get some time with a 3D printer to print a “proper” case for it.