Video RAM on /4 (1979) is the same as /4A ?

[globeron]

 

TI-99/4A Video RAM troubleshooting

https://www.ninerpedia.org/wiki/Troubleshooting

 

Are these issues similar related for the  /4 system ?

It only happens after 1-2 minutes when the system gets hotter 

(I also have normal screenshots after it has not been used for a while)

(I got some RAM chips, but before I start to replace them, could it be something else?)

 

 

 

 

 

 

Edited December 9, 2020 by globeron

[AwkwardPotato]

It's been a while since I replaced the VRAMs in a 99/4, but as I recall, they're laid out in the same order as they are on the 4A. The 4 uses the exact same kind of VRAM ICs as the 4A, so you might want to try the piggybacking method.

 

The lines at the bottom of the screen in your last picture are what worry me; those usually aren't a sign of VRAM failure, so you also might want to see what happens after swapping the VDP (9918A will work in place of the 9918).

[GDMike]

Green screen of death....ahhhh

[globeron]

6 hours ago, AwkwardPotato said:

It's been a while since I replaced the VRAMs in a 99/4, but as I recall, they're laid out in the same order as they are on the 4A. The 4 uses the exact same kind of VRAM ICs as the 4A, so you might want to try the piggybacking method.

 

The lines at the bottom of the screen in your last picture are what worry me; those usually aren't a sign of VRAM failure, so you also might want to see what happens after swapping the VDP (9918A will work in place of the 9918).

I will try the VDP as I guess itnis socketed. I have another /4, but a bit careful with it.  Maybe thermal paste is needed.  Bit will try he 9918A VDP chip.   Ps. Are 9918 chips still orderable? I remember i ordered somewhere in China but it got cancelled.

[globeron]

On 12/10/2020 at 11:26 PM, AwkwardPotato said:

It's been a while since I replaced the VRAMs in a 99/4, but as I recall, they're laid out in the same order as they are on the 4A. The 4 uses the exact same kind of VRAM ICs as the 4A, so you might want to try the piggybacking method.

 

The lines at the bottom of the screen in your last picture are what worry me; those usually aren't a sign of VRAM failure, so you also might want to see what happens after swapping the VDP (9918A will work in place of the 9918).

The VRAM has been replaced but now the output is only black and white (also when i put the originals back). Maybe now the crystal is broken? https://www.pagetable.com/?p=672

 

Or can it still have to do with a combination of VRAMs that effect the colors? I also tried the 9918A chip, same black and white result.

 

[globeron]

 

The colours and keyboard used to work, but I had the video issues already

 

 

Edited December 14, 2020 by globeron

[AwkwardPotato]

On 12/10/2020 at 6:09 PM, globeron said:

Maybe thermal paste is needed.  Bit will try he 9918A VDP chip.   Ps. Are 9918 chips still orderable?

Putting new thermal paste on the VDP is always a good idea. I don't know of a source for the original 9918, sadly 

15 hours ago, globeron said:

The VRAM has been replaced but now the output is only black and white (also when i put the originals back). Maybe now the crystal is broken?

Did replacing the VRAM have an impact on the corruption?

 

I can't tell for sure, but it looks like there is color, just very washed out. Does your GBS 8200 (VGA converter) board work with a different TI? I ask because mine always puts out the wrong colors when used with my TIs. 

[globeron]

I ordered a 9918A via ali express and will try.

 

The black and white screen captures. One is with a Pal modulator  and the one with a bit of colour is gbs8200 (which maybe spreads out colour)

 

But was wondering if it can have to do with

https://www.ninerpedia.org/wiki/Troubleshooting  there are some Vram that change.color (red green blue). Bit 5 6 7  ?

[AwkwardPotato]

VRAM shouldn't make the video go black-and-white. It definitely could be that the crystal has gone bad / out-of-spec. There's a variable inductor right next to the crystal that I believe fine-tunes the frequency; maybe you can see if adjusting it brings the color back?

 

EDIT: This is really important, the part of the inductor that you adjust is very brittle, so be super gentle with it!

Edited December 15, 2020 by AwkwardPotato

[globeron]

I changed the 9918 to 9918A (seems he 9918 gave some visualisation problems when it becomes hotter, i did not try thermal paste yet).

 

I tried different PAL modulators, one gives me this type of colours in the video.   Maybe it is the crystal related?   (As i tested the PAL modulator on my TI-99/4A and gives a good video output)

[globeron]

I do not get any output via gbs8200 using the /4, but it is okay with /4a.

seems some video synchronization issues. I did try the variable inductor, I do not see a change and now not sure if it is back to set to original setting.

[GDMike]

No, but i bet HBO comes in clearly now!!

Keep trying, your almost there.

[AwkwardPotato]

2 hours ago, globeron said:

I changed the 9918 to 9918A (seems he 9918 gave some visualisation problems when it becomes hotter, i did not try thermal paste yet).

 

I tried different PAL modulators, one gives me this type of colours in the video.   Maybe it is the crystal related?   (As i tested the PAL modulator on my TI-99/4A and gives a good video output)

 

2 hours ago, globeron said:

I do not get any output via gbs8200 using the /4, but it is okay with /4a.

seems some video synchronization issues. I did try the variable inductor, I do not see a change and now not sure if it is back to set to original setting.

Those colors are weird for sure. Chances are it is the crystal, so no harm in replacing it. I know that the 99/4 has a potentiometer towards the back of the board unlike the 4A; tomorrow I'll open mine up and mess with it to see if it could cause something like this. I also wonder if this could have something to do with an NTSC/PAL problem...

[globeron]

I changed the 9918 to 9918A (seems he 9918 gave some visualisation problems when it becomes hotter, i did not try thermal paste yet).

 

I tried different PAL modulators, one gives me this type of colours in the video.   Maybe it is the crystal related?   (As i tested the PAL modulator on my TI-99/4A and gives a good video output)

[globeron]

I have it working now, but only with GBS8200 device.

 

First I replaced the crystal from another /4A, did not make a difference.

 

Then replaced with another 9918A chip of my european ti/4a PAL. (maybe the other chip is a 9928 as that was a usa console NTSC) of another /4A, then it suddenly worked with the GBS8200, but the PAL is weird enough still black and white. Not sure if there is a difference?

 

The original 9918 chip shows the screen completely scrambled.

 

The /4 is a European console with DIN6 pin,

But now with GBS 8200 is sharp (and a bit flattened colors as expected).

 

 

Parsec still does not work with 9918A chip in a /4 console.

 

 

 

 

 

Furthermore i wanted to troubleshoot with the F18A card, but I cannot fit it in a /4, because of the orange component.

 

 

 

 

[globeron]

Also noticed when assembling all together that the keyboard metal connectors touches the metal coverage and gives keyboard errors.

 

Here it is fully assembled

TI-99/4 with built-in Speaker and earpiece connector.

 

 

 

 

This TI has the power connector with

the BIG pin. As the original power brick was broken a long time ago a converter was made with a meanwell adapter.

 

 

 

 

 

 

[AwkwardPotato]

11 hours ago, globeron said:

Then replaced with another 9918A chip of my european ti/4a PAL. (maybe the other chip is a 9928 as that was a usa console NTSC) of another /4A, then it suddenly worked with the GBS8200, but the PAL is weird enough still black and white. Not sure if there is a difference?

 

The original 9918 chip shows the screen completely scrambled.

 

The /4 is a European console with DIN6 pin,

I'm surprised that the European 4A had a 9918A in it, and that the 4 used to work with a PAL modulator, because both the 9918 and 9918A are NTSC chips. AFAIK TI never shipped a system with the 9928(A) in it. 

11 hours ago, globeron said:

Parsec still does not work with 9918A chip in a /4 console.

Sadly, most software that won't normally run on a 4 still won't run after installing a 9918A. Probably down to ROM/GROM differences.

 

Glad to see that you found what was causing the keyboard problem, and to see the 99/4 mostly working 

 

[AwkwardPotato]

Wait, I thought all 99/4s were NTSC units with the original 9918, and European users could only use them with TI's NTSC monitor. But the GBS8200 doesn't work with the composite output of the 9918(A), it needs the YPbPr output from a 9928/29. Is the VDP that came in your 99/4 labelled as a 9918, or something else?

[globeron]

39 minutes ago, AwkwardPotato said:

Wait, I thought all 99/4s were NTSC units with the original 9918, and European users could only use them with TI's NTSC monitor. But the GBS8200 doesn't work with the composite output of the 9918(A), it needs the YPbPr output from a 9928/29. Is the VDP that came in your 99/4 labelled as a 9918, or something else?

 

I cannot read the label anymore on the chip, it is all washed out, but you are right I think I switched the numbers.

 

European consoles Din 6 pin have YPbPr component output which works with GBS8200

Then it is probably a 9928 chip and it explains why the 9928A chip? of my european /4A works.

 

(The earlier tests where with a chip of a /4A of the US, 5 Din plug which is 9918A and NTSC)

 

I have another /4 of USA with a 5 DIN plug which works with a composite cable directly into the TV. (This one is then the one with the 9918 chip in it).

 

There is somewhere a link which describes the differences between pins on the 9918 and 9928 chips.

 

Edit:

Link http://www.unige.ch/medecine/nouspikel/ti99/tms9918a.htm

Edited December 19, 2020 by globeron

[AwkwardPotato]

Thanks, that makes more sense. I never knew the 99/4 could come with a 9928/29, everything I recall reading online suggested to me that they only came with 9918s.

[globeron]

11 hours ago, AwkwardPotato said:

Thanks, that makes more sense. I never knew the 99/4 could come with a 9928/29, everything I recall reading online suggested to me that they only came with 9918s.

This is the original chip. I put the sticker on it as otherwise i cannot identify how to insert it.

[Retrospect]

19 hours ago, AwkwardPotato said:

Wait, I thought all 99/4s were NTSC units with the original 9918, and European users could only use them with TI's NTSC monitor. But the GBS8200 doesn't work with the composite output of the 9918(A), it needs the YPbPr output from a 9928/29. Is the VDP that came in your 99/4 labelled as a 9918, or something else?

Hi .  Some time during 1982, a certain computer shop in the UK started selling the 99/4 on it's own with no monitor for £250.... So there must of been PAL versions that worked with our TV's.  

[jens-eike]

Yes, my first computer was a TI-99/4 with PAL modulator (and internal speaker/pot). TI abandoned the NTSC monitor bundling before and used the TMS9929 (no A).

[jens-eike]

On 12/20/2020 at 10:01 AM, globeron said:

This is the original chip. I put the sticker on it as otherwise i cannot identify how to insert it.

It is clearly marked already: TI used the groove at the side of pin 1 (to 20) on many chips in the 1970s

[globeron]

On 12/24/2020 at 4:29 AM, jens-eike said:

It is clearly marked already: TI used the groove at the side of pin 1 (to 20) on many chips in the 1970s

Thanks Jens-Eike. I will check it again when back. Did not notice that earlier.