Ti-99/4A possibly overheating?

[Diesel419]

To start I want to preface this by saying I am VERY NEW to the world of TI-99 4/A computing, so my apologies for my ignorance.

 

My 99 is my first vintage computer and I only just got it. Also I have no cartridges yet so all I've done is start learning basic.

 

The computer boots perfectly and runs very well for about 10 ish minutes.

 

At about that time the machine starts a gradual descent into graphical corruption that ultimately ends with the screen turning into nothing but a corrupted mess.

 

In addition even the simplest basic programs right out of the original ti basic textbook won't execute properly during this process, constantly running into errors that aren't there.

 

The reason I believe this is heat related is that if you simply turn the machine off and back on again it immediately starts to corrupt again. 

 

But if you turn off the machine and walk away for a few minutes, then the computer starts to work correctly, for about 10ish minutes again.

 

Any suggestions on what might be the problem?

 

 

Edited October 26, 2022 by Diesel419

[HOME AUTOMATION]

Sounds like it could be the VRAM, or perhaps the VDP, itself. Can't rule out the power supply board though...

[+retroclouds]

Yes, also think that it is the video ram. It would explain why the basic programs don’t work, because that is where TI-Basic stores the tokenized version of the program.

[matthew180]

The VDP (9918A) in the 99/4A requires a heat sink.  If the console has been opened before, the heat-sink may not have been reinstalled properly.  Alternatively the heat-sink thermal paste is surely dried out by now and should be removed and replaced with fresh paste.  Just use the same stuff you find online for modern CPU coolers and such, it won't take very much.

 

I don't know that I have heard of the DRAM overheating.  I'm not sure if video corruption would be a symptom of power supply going bad.  But the voltages are easy enough to test with a basic volt meter.

[Duewester]

First, as a former trainer in the Navy and in maintenance for a fortune 100 company, don't apologize for ignorance. Ignorance is just a matter of not knowing and that can be fixed by learning. Stupid- is a conscious decision to ignore what you know.

Second. welcome to the world of Ti-99 4a.

Well, as discussed in another topic in this forum, you could use an old AT power supply to bump in power and see if that works. While you're in there replacing the thermal paste on the vdp is a good idea.

Me personally, I think opening up a 40+ year old console and inspecting it for visual problems is a good idea anyway. Even if it has never been opened before inspecting it can't hurt. I bought one on Ebay that looked almost like it just rolled out the factory door but when I opened it (fortunately I hadn't powered it on) the RF shield was bent and twisted and not only contacting the shield/ground, it was in contact with several other components - an IC, some resistors, and had no thermal paste on the VDP or the socketed 9904. So someone had been inside and did a real sloppy job of putting it back together. Turned out the power wart transformer was bad too.

[+arcadeshopper]

- dram overheats and dies over time.. best to replace with modified 4164's no this doesn't get you 64k ram, just uses them as 16k

- original linier power supplies are very warm, I put a fan on the vents to draw out heat on hot days/long term use or replace with the qi switching ps

- vdp overheats cooks and heatsink compound is pretty much dried up after 35-40 years, needs to be replaced at the very least.. 

 

 

 

[Switch1995]

Any of the "regulars" on here using this?:

 

https://www.keelog.com/ti-99-4a-psu-modern-gray-au-replacement-ti-99-4a-power-supply-au-plug/

[matthew180]

Wow, I have never seen those!  Nice looking units, good info, it looks like a lot of effort went into making them.  Seems like nice quality.

 

However, my main concern is in using the same external socket as the original power supply, with incompatible voltages.  The rewiring to bypass the internal power board is left as an exercise for the user.  Despite the warnings on the site, people *will* buy this an just plug it in.

 

It seems a different external plug and socket would have been a better solution, with the final piece being an internal cable assembly that connects the different external socket to the 4-pin power input on the motherboard.  This way you only have to open your 99/4A, disconnect and remove the power supply board, install the internal adapter cable, close it back up, and plug in the new external supply (to its "different from stock 99/4A" power socket).

 

[+arcadeshopper]

1 hour ago, Switch1995 said:

Any of the "regulars" on here using this?:

 

https://www.keelog.com/ti-99-4a-psu-modern-gray-au-replacement-ti-99-4a-power-supply-au-plug/

 

no because it requires rewiring your console to non-standard voltages. This is a recipe for catastrophic failure in the future by someone plugging in the original AC supply into a DC connector.. 

[Switch1995]

1 hour ago, matthew180 said:

external plug and socket would have been a better solution, with the final piece being an internal cable assembly that connects the different external socket to the 4-pin power input on the motherboard

That might be an interesting little product by itself.  Are the 4-pin "molex" inputs to the motherboard standard across the many "flavors" of the 4/4A?  Maybe the housing for the external socket could be orange as a "warning" for future users.

 

https://www.cablesforless.com/custom-cables/

 

Also, is the external plug a standard that could be communicated to a service like I link above?  

 

Edited October 26, 2022 by Switch1995

[Diesel419]

So after reading all the advice you folks have provided, here's what I'm going to do.

 

Replacing the thermal paste is the only thing I can do without ordering more parts, so I'll do that tonight, And post an update.

 

Beyond that, what would be the best way to test things like the power board and the VRAM?

 

Edited October 26, 2022 by Diesel419
Grammar

[Duewester]

3 hours ago, Switch1995 said:

Any of the "regulars" on here using this?:

I saw two ladies on YouTube extolling the virtues of the ps. I looked into it and ordered one. Now I currently have a BBB case on file about them. I ordered one, got charged for it immediately and never heard another word from them. When I inquired, I got delaying tactics until my bank would no longer cancel the obvious fraudulent charge.

Hope you have better luck. 

[Switch1995]

Just now, Duewester said:

I saw two ladies on YouTube extolling the virtues of the ps. I looked into it and ordered one. Now I currently have a BBB case on file about them. I ordered one, got charged for it immediately and never heard another word from them. When I inquired, I got delaying tactics until my bank would no longer cancel the obvious fraudulent charge.

Hope you have better luck. 

Wow!   That's all I need to hear.  This might have been the shortest time a project was checked off my list  

[Diesel419]

Ok, I have pulled apart the computer, put new thermal paste on the VDP,  reconnected everything as shown in the photo, and tested the machine.

The length of time from startup to unusable has gone from 10 ish minutes to 30 ish minutes, but that's not the most interesting part.

 

By spraying duster gas onto the VDP both onto the heatsink and directly through the holes, I can halt or even reverse the effects.

 

I'm assuming then that replacing the VDP might be my best course of action.

 

If so, where would be the best place to get a replacement?  Preferably a place where I don't have to deal with shipping from China.

 

Edited October 27, 2022 by Diesel419

[+9640News]

Last night, I discovered on Ebay someone selling two untested TI's not more than 3 miles from my house.  I went over and both TI's were in working order that I picked up at a good price.

 

The "brick" power supply cord "hummms" quite a bit.  I can't say I have ever heard a power supply hummm before.  Not that I need the power supply, but are there people using power supplies that hummm, or is it an indication of a potential failure near term?

 

Beery

 

[Duewester]

12 hours ago, Diesel419 said:

If so, where would be the best place to get a replacement?  Preferably a place where I don't have to deal with shipping from China.

I sent you a message.

[matthew180]

21 hours ago, Diesel419 said:

If so, where would be the best place to get a replacement?

 

An F18A would fix your problem, if only they were available!  What the hell is that guy up to anyway?  I should go check the status on that project...

[+arcadeshopper]

On 10/26/2022 at 11:58 AM, Duewester said:

I saw two ladies on YouTube extolling the virtues of the ps. I looked into it and ordered one. Now I currently have a BBB case on file about them. I ordered one, got charged for it immediately and never heard another word from them. When I inquired, I got delaying tactics until my bank would no longer cancel the obvious fraudulent charge.

Hope you have better luck. 

BBB is a marketing company.. don't waste time with them they can't do anything but badger them to sign up for their club ..  call the local district attorney in their location

 

 

[+OLD CS1]

4 minutes ago, matthew180 said:

 

An F18A would fix your problem, if only they were available!  What the hell is that guy up to anyway?  I should go check the status on that project...

Probably being lazy and planning for Free Play and getting hold of that sweet, sweet PCjr.

[Duewester]

1 hour ago, OLD CS1 said:

Probably being lazy and planning for Free Play and getting hold of that sweet, sweet PCjr.

Actually I think I read that the chip shortage got him. Working on the V2 mostly. Saw a couple of V1's listed here a while back but they didn't last long.

Gotta say, even the V1 is awesome. 

[+OLD CS1]

1 minute ago, Duewester said:

Actually I think I read that the chip shortage got him. Working on the V2 mostly. Saw a couple of V1's listed here a while back but they didn't last long.

Gotta say, even the V1 is awesome. 

Propaganda.

[Diesel419]

1 hour ago, matthew180 said:

 

An F18A would fix your problem, if only they were available!  What the hell is that guy up to anyway?  I should go check the status on that project...

Oh believe me sir, if I could, I would.  I've been scouting for upgrades since before I even received the machine, with that total piece of unobtainium being near the top of my list.

[+arcadeshopper]

2 hours ago, Diesel419 said:

Oh believe me sir, if I could, I would.  I've been scouting for upgrades since before I even received the machine, with that total piece of unobtainium being near the top of my list.

hmm just had 20 in my store a month ago.. course they are stuck in customs     sold quick!

 

[Diesel419]

With a new-used VDP installed the overheating issues with my TI-99 have vanished!

 

Now to find a disk solution that doesn't cost more than twice what I paid for the computer.

[Duewester]

@Diesel419 Glad to hear it. Disk solution - TiPi. Plenty of talk about it here in the forums. You're gonna need a Raspberry Pi though and they aren't cheap at the moment. Scalpers gobble em up and charge too much for them. Keep an open on the Adafruit.com web site at 11:30 am on Wednesdays. Lady Ada puts her new stock from the Raspberry Pi org on the shelf. You'll need to have a verified account to order one so log in a few minutes early. Heads up though. Shipping will be expensive if you go their UPS regular method. I almost always go USPS.