Failing TI-99, worth repairing?

[INTVCruise]

I have a white case, white keyboard TI-99 that seems to work, other than it has no color, so black and white (I think the crystal is bad?), and the video becomes unstable and garbage starts to fill the screen after about 5 minutes of being on, screen also shakes and cuts in an out. I have another TI-99 with a black screen and beep noise that I could salvage parts from, it is a silver case black keyboard version. Are these two versions the same on the inside chip-wise? I think the issue of garbage on the screen is due to bad Vram, is that right? Thanks everyone!

[RickyDean]

15 minutes ago, INTVCruise said:

I have a white case, white keyboard TI-99 that seems to work, other than it has no color, so black and white (I think the crystal is bad?), and the video becomes unstable and garbage starts to fill the screen after about 5 minutes of being on, screen also shakes and cuts in an out. I have another TI-99 with a black screen and beep noise that I could salvage parts from, it is a silver case black keyboard version. Are these two versions the same on the inside chip-wise? I think the issue of garbage on the screen is due to bad Vram, is that right? Thanks everyone!

 

The garbage is probably Vram, and there is a guide to diagnose, not sure where that is. But you also might consider a pico9918 from @arcadeshopper, or a DIY Tang 9K VDP replacement, to eliminate the VDP altogether. FYI

 

 

Edited September 24 by RickyDean
spelling

[INTVCruise]

5 minutes ago, RickyDean said:

The garbage is probably Vram, and there is a guide to diagnose, not sure where that is. But you also might consider a pico9918 from @arcadeshopper, or a DIY Tang 9K VDP replacement, to eliminate the VDP altogether. FYI

 

 

Thanks Ricky, ill probabaly just try to keep it stock if it's possible. If I can't fix it with the other dead one ill probably just piece it out, the keyboard is one of the nice mechanical ones, probably worth more by itself than the rest of the computer lol. 

[+mizapf]

See Ninerpedia for a simulation of VRAM defects (section Troubleshooting).

[RickyDean]

2 hours ago, INTVCruise said:

Thanks Ricky, ill probabaly just try to keep it stock if it's possible. If I can't fix it with the other dead one ill probably just piece it out, the keyboard is one of the nice mechanical ones, probably worth more by itself than the rest of the computer lol. 

Understood, just bear in mind that both of these are plug and play pretty much. You just have to decide how to best run the VGA/HDMI cable and adapter out of the TI to use it.

[JB]

7 hours ago, INTVCruise said:

Are these two versions the same on the inside chip-wise? I think the issue of garbage on the screen is due to bad Vram, is that right?

They're mostly the same. The video section in particular is identical chips, so stealing VRAM from one to fix the other should work just fine.

[+bent_pin]

I'll be interested in all the excess parts when you are finished.

[INTVCruise]

Thanks everyone who posted, and just to confirm, the crystal replacement should bring back the color correct? That's what I read, but if I don't need to swap it I'd rather hold off on doing it and save the potentially good crystal for later. 

[Gary from OPA]

5 minutes ago, INTVCruise said:

Thanks everyone who posted, and just to confirm, the crystal replacement should bring back the color correct? That's what I read, but if I don't need to swap it I'd rather hold off on doing it and save the potentially good crystal for later. 

Do you know if it's a ntsc or pal console.

 

Is your video DIN plug 6 pins or 5 pins?

Is your VDP the 9918 or the 9928.

 

Lack of color and screen shaking and cutting in and out, could also be because you have a PAL console running on a NTSC monitor or vice-versa.

[INTVCruise]

Hi gary it should be ntsc I bought it here in the usa. So the vdp is 9918 and the video output is 5 pin. 

[INTVCruise]

Just now, INTVCruise said:

Hi gary it should be ntsc I bought it here in the usa. So the vdp is 9918 and the video output is 5 pin. 

The screen is stable at first for about 1.minute. then gets glitchy like thisnsome.times.

[+OLD CS1]

2 hours ago, INTVCruise said:

Thanks everyone who posted, and just to confirm, the crystal replacement should bring back the color correct? That's what I read, but if I don't need to swap it I'd rather hold off on doing it and save the potentially good crystal for later. 

Could be: https://www.pagetable.com/?p=672