TI99 Video Issue

[Pagan]

I have an extra TI99 that has a serious issue and I'm not sure where to start. As far as I can test without replacing every one of them the 4116's all seem to be fine. I've redone a few other boards with 4116s video issues but this seems to be elsewhere.

 

Basically all I get is static garbage moving fast across the screen. My first though is a bad video out and sometimes I get sound and sometimes nothing. I recorded a short video of it, pardon the crappy S5 being held shakily as I toggle the power on and off a few times. The cables/power adapter being used all work on another system with no issues and the game used has no impact on the result.

 

 

 

[Stuart]

Don't think this is a 4116 memory problem - with a bad memory chip you'll get a stable display but corrupted characters.

 

Suggest removing the motherboard and checking if the video connector has come loose and broken the soldered connection to the video signal. (Alternatively try wiggling the video cable while it is powered on and see if the picture appears.

 

Next I'd try replacing the TMS9918A and next the crystal. Or fit an F18A.

[Shift838]

i had this exact same issue on one of my consoles and it was my TMS9918A. Luckily I had a good one that I pulled out of a unit that I equipped with the F18A video upgrade and it was a quick fix.

 

I have since purchased a new F18A for it, but have not yet installed it.

[Omega-TI]

 

I have since purchased a new F18A for it, but have not yet installed it.

 

That sir is a crime!

[Shift838]

 

That sir is a crime!

 

yea I know. I at least have the F18A installed in my primary 4A. my backup I have it ready to go in. just got to find the time. Guess I need to carve out an hour or so and put the guitar down and just get it installed.

[Pagan]

So after swapping the 9918A with another one, same issue. Testing the "bad 9918A" on another motherboard and it worked without an issue so it seems my problem lies a bit deeper.

Edited July 25, 2016 by Pagan

[Tursi]

Are you sure you don't just have a broken wire in the video cable? That's what it looks like here. Audio sounds crisp.

 

Your testing suggests problem between VDP and monitor... the cable is the most likely culprit and easiest to test. Otherwise, something may be messed up on the board, check for physical damage, swollen caps, etc, in the video output area.

[Timw]

My 99/4A has a similar video issue as above, except that it starts out with a good display which then slowly degenerates over about 20 minutes to the same "static garbage" as in the original post. Leaving it powered off for 30 minutes restores the good display, so I deduce it's something to do with internal temperature rise.

 

It has the same issue when connecting the component output to a digital TV, so it's not a faulty cable or modulator. I've tried replacing the video chip headsink compound without seeing any improvement.

 

This is a machine I'm trying to decide if I can resurrect after 25 years stored in the attic. I'd be glad to know if the OP, or anyone else, has found a solution.

[Tursi]

It would be interesting to know. My first instinct is that it doesn't sound like the VDP is failing, but there is an analog video amp between the VDP and the port on the rear of the console. Since it looks like no video signal (rather than corrupted data), I'd lean towards a cap or transistor in that circuit.

[Omega-TI]

It would be interesting to know. My first instinct is that it doesn't sound like the VDP is failing, but there is an analog video amp between the VDP and the port on the rear of the console. Since it looks like no video signal (rather than corrupted data), I'd lean towards a cap or transistor in that circuit.

 

One of the easiest test methods for thermal variance -----> << CLICK HERE >>

 

[Timw]

OK, thanks for the suggestions. Looks like I'll need to take it apart again for a closer look.

[LynxHandyCaster]

Don't know if this will help but:

 

I had a similar problem with my Atari 130XE 8-bit a while back. The colors on screen would start to roll over a 5-to-10-minute period after turning it on. The good folks here on the AtariAge Forums were correctly able to identify the problem as a failing power supply.

 

I know comparing the TI to an Atari 8-bit is like comparing apples to oranges, and the experts here are welcome to chime in: could the issue lie with the power supply?

[+Lee Stewart]

Don't know if this will help but:

 

I had a similar problem with my Atari 130XE 8-bit a while back. The colors on screen would start to roll over a 5-to-10-minute period after turning it on. The good folks here on the AtariAge Forums were correctly able to identify the problem as a failing power supply.

 

I know comparing the TI to an Atari 8-bit is like comparing apples to oranges, and the experts here are welcome to chime in: could the issue lie with the power supply?

 

Monitor or computer power supply?

 

...lee

[LynxHandyCaster]

Power brick for the TI console itself.

[LynxHandyCaster]

I hope I'm not being presumptuous here (because this is the kind of mistake I myself have made), but are you certain that your TV/monitor and modulator switch are both set to the same channel?

Edited August 24, 2016 by MillipedeMan

[Shift838]

I hope I'm not being presumptuous here (because this is the kind of mistake I myself have made), but are you certain that your TV/monitor and modulator switch are both set to the same channel?

 

Good question!.. I myself did that years ago. There is a switch on the RF modulator for channel 3 or 4.

 

Most of us like myself take it for granted since we no longer use an RF modulator and use just RCA cables to a newer type LCD or have converted to the F18A.

 

I have seen this exact issue if the RF is not set to the correct channel that you are on and you just get sound.

 

I have also seen that the RF modulator can go bad and only produce video and no sound or vice versa.

 

One easy way to rule out the RF modulator is to hook it up to a newer LCD TV or Tube TV that has RCA audio jacks and video jack.

 

If you need instructions for the cable, you can find it HERE

[Omega-TI]

Also, for people who do not want to break out a soldering iron, there is << THIS OPTION >> .

It's currently selling for $8.56 USD with the shipping included. I ordered one today myself for the annual giveaway machine.

 

[Sinphaltimus]

 

One easy way to rule out the RF modulator is to hook it up to a newer LCD TV or Tube TV that has RCA audio jacks and video jack.

 

If you need instructions for the cable, you can find it HERE

Hmm, that link doesn't seem to work.

 

When I got my new old TI a little over a month ago, I could not get my RF modulator to work, looked like the video above. So I purchased another and had the same issue. I found the rf mod hack to composite video instructions and gave it a go. Easiest soldering job ever, works like a charm.

 

Here's another link in case the above one still doesn't work.

 

http://www.instructables.com/id/DIY-TI-994a-Composite-Video-Cable/

Edited August 25, 2016 by Sinphaltimus

[+Lee Stewart]

Hmm, that link doesn't seem to work.

...

 

It works for me.

 

...lee

[Sinphaltimus]

 

It works for me.

 

...lee

It works now, on my phone at least. At home this morning it didn't.