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Ready to explore TI-99/4A after months of troubleshooting!


New Member
May 29, 2019
Finally, after months of limited time and testing a lot of random things, I managed to fix both of my TI-99/4As to perfect operation! In the process I went down the rabbit hole of understanding production revisions and became much more familiar with the hardware. My first experience with the TI-99 was in the 1990s when I found one at a thrift store. But it only contained TI-Invaders and no documentation so it wound up binned. But this past year I became more intrigued by it again and had a couple other machines I'd accumulated so thought to get everything up and running!


Silver Model (2nd Run)

This is the second run that doesn't contain the "Solid State Software" emblem (which in early runs had filled in the volume slider cut-out of the early TI-99/4). This had become extraordinarily corrupt months ago (not the typical RAM symptoms) after I accidentally left it on for days. There was one bad VDP RAM but more going on. I replaced TMS9918 and GROMs as well. But most often it'd just be solid black with a constant tone, eventually ruled it down to CPU malfunction. In the process I enjoyed watching the three part series from Adrian's Digital Basement where he troubleshot a similarly defected TI-99 and after replacing most components his conclusion was that the CPU was the culprit all along but other things went bad as part of the troubleshooting process. The lack of sockets on almost every chip including the beast of a 64-pin CPU made I tedious to add ones and test. In any case it now has all working chips again and I added fresh arctic paste to the VDC, which I recommend everyone doing if they have it disassembled as the original paste will be long dried up and ineffective. This one has an ALPS keyboard and everything works perfectly.

Beige Model (QI, Pre-2.2)

Interestingly, the beige model I had, which only had a bad keyboard, is a Frankenstein monster cross between the original Beige and the QI version. The actual molding, mainboard PCB and RF shields were all from the QI rearrangement (including shielding above the keyboard and no front-side shielding). Yet the power supply was still the original four-pin style, but is possible it had been replaced at some point. The best part is that it was still on the 1981 ROM, so does not suffer the third party blocking that v2.2 brought. The keyboard it had was the terrible mylar style and very few keys were working. Repairing these can be hit-or-miss, but luckily I had a second dead parts unit I picked up many years ago from a garage sale for a few bucks. That one contained an ALPS switch keyboard. I swapped it into the beige QI and it works perfectly. I still intend to use the silver as my primary unit as it matches the speech synthesizer, and FinalGROM seemed to behave a bit better with the silver model in my early testing.


I have what I'd consider a pretty decent setup for the TI-99/4A now.
  • Accessories from Arcade Shopper including the Brewing Academy FinalGROM99 multicart with 16GB SD, composite cable and 32K Sidecar Memory Expansion.
  • Original speech synthesizer
  • Two pairs of original working controllers
  • TexElec's TI-99/4A to Atari 2600 Style Joystick Adapter
  • Nintendo-style TI-99 controller for single-player gaming from retrogameboyzcom
  • A box full of original carts, manuals and case cover from a friend on Facebook.
While digging through old bins of parts I had this weekend to find my old controllers and parts machine, I found more TI-99 catalogs and documents which also included a full paperback TI-99 book "Time Lost" that is part comic book, part programming. I looked it up and found an old thread on AA that discussed it. Apparently the paperback form is quite obscure, mine was just in a box with other TI-99 stuff I picked up from a sale but then forgot about. There is a digital PDF version here.

Looking forward to discovering the TI-99 world in the months to come!

Agent Orange

Veteran Member
Sep 24, 2008
Hey Matt, looks like you did yeoman's work on you TI setup, and it's great looking. Don't be a stranger here.