View Full Version : TT-99/4A Bad Graphics and Black Screens

May 5th, 2015, 03:23 PM
I have quiet a few TI99/4A

Lets started with the bad graphics:

The start screen on two of them is all scrambled. When I connect the keyboard and try to press a key it goes all wacky on one of them. Have not turned the other one on in a while, but it had the same scrambled graphics. I know this means bad VRAM more than likely.

Could you tell me where to purchase the RAM for an affordable price? I have a bunch of sockets already so I'm good there, but I may need more:))


The other two I have just make a loud beep with a black screen. I know this means the sound processor is not being initialized. Any recommendations for where to start? I already reseated the reseatable chips. Thanks!

May 12th, 2015, 12:43 AM
Well, if you see scrambled graphics and see the Ti reacts to keypresses it probably must be bad VRAM. If you have at least a good spare 4116 IC, you can try to piggyback it over each one of the PCB RAMs looking for changes, sometimes this method gives good results. Try it ONLY if the ICs are cold (obviously a HOT IC it's always very suspicious ;-))
You don't need to purchase a lot of replacements, if you're able to desolder all of them and place sockets, you can check it one by one. If you only have a bad IC you'll find it for sure :-)

About the black screen, check first the usual: voltages. Check the three voltages in 4116 ICs are correct. Inspect PCB for damaged components and reseat all ICs placed in sockets. Look for hot ICs. Next try to swap the socketed ICs. Last, focus your work in the 4116 RAMs, they're extremely prone to faults.

Good luck!