It came complete with power supply and RF-modulator. The RF-Modulator was a bit of a surprise. So far I had not encountered a computer that used an external one, and certainly not such a huge, heavy black box as this one. Fortunately the output leading to the modulator carries standard YUV (or Component Video) signal, which is supported by my GBS8200 Video Converter Board.
|The TMS9900, one of the first 16-bit processors.|
So it has to come apart..
illustrated instructions on Mainbyte, this is easy. And I soon find out that tapping the 'power bar' that runs past all the video RAM chips causes flicker and the changing of the characters. After touching all solder joints with my iron and some fresh solder the video problems are greatly reduced.
Now for the keyboard. Initially I suspect the keyboard scanning chips and resistors. But after checking the signals with an oscilloscope it soon shows that the keyboard contacts are causing the problem.
The TI99/4a has been produced with several different types of keyboards, and mine appears to contain the worst of all: the 'Mitsumi' membrane based keyboard.
After posting this question to the Retrocomputing StackExchage, I followed the advice and cleaned both sides with 'Chemtronic Pow-R-Wash', a contact cleaner the leaves no residue, and I gently rubbed the contact carbon using an eraser. The keyboard now seems to work great again, not sure how long this will last though.
Meanwhile the video failed again. And after a lot of tinkering the system does not work at all. It looks like the 5V is down, but when I disconnect the PSU the 5 V is correct. So it looks like there's a short circuit somewhere.
What puzzles me are the white bars, which I expected to be full metal bars carrying either power or ground. But that does not match the connections to the RAM chips. It looks like its bot conected to the 5V and the GND pins.
I found the following comment on the 'AtariAge' forum:
"that the 'weird rails' are actually two metal strips with a paper separator, and actually carry both +5V and GND. By trimming it, you've possibly created a short circuit and/or you've only jumpered one side of it. I'd give that a careful inspection."
Right. I did not expect that. And this means I probably created a short somewhere. Looking further I found it's even worse. The bars may also carry
|1.With bar. 2.Bar removed. 3.New connections.|
It the end I just removed the complete bar. Which indeed solved the short circuit, suggesting I was on the right track. So I just wired all 5V and 12V points manually using some solid wire. Which worked. Video is back again and the computer runs as normal.
Unfortunately it failed again after a week, same problem. So the short must be somewhere else. I suspect a capacitor, but finding that will be a lot of work.
The FlashRom99 Module is created by Ralph Benzinger and uses a Secure Digital (SD) Card for storing ROM images. After power up the content of the SD Card is displayed in a menu. When a selection is made the ROM image is read from he SD card by the ATMEGA8515 CPU on the module and copied to the 32KB RAM chip. It's available as fully built cartridge, a complete kit, or just the PCB with a programmed CPU. I chose the last one. After all, building is 90% of the fun.
Assembly was really easy, and it worked immediately.
The .zip file that can be downloaded from the FlashRom site contains a bunch of sample games and programs so you can get started right away.
A set of useful utilities like an editor/assembler, ready for installation on the FlashRom can be found on the TI99 site of Fred Kaal
Useful links for the TI99/4AThe MainByte site has got a lot of really good information.
Stephen Shaw's 'Getting Started' book online.
Ninerpedia. The Wiki for TI-99/4A, TI-99/8, Geneve 9640, and all related hardware and software.
The TI99/4A Forum on AtariAge
A recent article on The Register about the increasing popularity of the TI-99.