Texas Instruments TI-99/4A fix

Seek advice, give advice or tell others about your repair and restoration projects

Texas Instruments TI-99/4A fix

Postby tezza on Sun Feb 09, 2014 3:41 pm

I've become interested in the Texas Instruments TI-99/4a after getting a battered and non-working one in the great Wellington give away.

I've got a nice case coming from the US and I ordered a working PAL board from Spain (EBAY). The latter arrived last week. I tried it out today.

Did I say working? Well....yes. But only for about 40 seconds at a time. After that the picture started to drift then break up. Switching off for a few minutes then on again got the screen back....but again only for 30 to 40 seconds.

So, something heat related then I figured. probably a passive component going out of tolerance as it warmed up. I noticed that there was a power dip in one of the video pins after about 40 seconds which corresponded to the image break up. I traced the fault back through the video circuit, and (eventually!) found the problem. This large orange capacitor you see in the picture.


Swapped it out with the same cap in my spares board and now I see this! (black line at the bottom is camera/strobe effect)


Image remained stable for 15 minutes. Played around in BASIC a bit. Looks like it's fixed.
Tez (Terry Stewart) (Administrator)
Collection: https://www.classic-computers.org.nz/co ... /index.htm
Projects and Articles: https://www.classic-computers.org.nz/blog/index.htm
Twitter: @classiccomputNZ | YouTube: Terry Stewart
Trade Me: tezza5
Site Admin
Posts: 2380
Joined: Thu Jan 01, 1970 12:00 pm
Location: Palmerston North, New Zealand

Re: Texas Instruments TI-99/4A fix

Postby SpidersWeb on Thu Feb 20, 2014 10:19 am

Nice! After seeing the adverts online, now all I can think of is Bill Cosby.
Just need to grab one of these: http://www.vintage-computer.com/vcforum ... -System%29
(Spotted it this morning)
Wanted - Dead or Alive - Reward $$$: Compaq Deskpro 8088 / 286 / 386 - IBM RT 6150/6151 parts - AT&T 3B2 parts
VC Twitter
Posts: 1133
Joined: Tue Jan 24, 2012 8:38 am
Location: Wellington

Return to Repair and Restoration

Who is online

Users browsing this forum: No registered users and 5 guests