jschaap26
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Posts posted by jschaap26
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On 12/15/2019 at 4:04 PM, AwkwardPotato said:
Try applying new thermal paste on the stock RF shield/heatsink and see if the problem goes away. If the system still acts up afterwards, there's a good chance that the 9918A is failing (chips aren't always completely non-functional when they're damaged).
If a VDP can't stay stable even with refreshed thermal paste on the stock heatsink, it's a better idea to replace it than cut up the shield/install heat pipes/custom heatsink, since the problem will likely only continue to get worse.
Thanks for your thoughts. Yeah, I have applied modern thermal paste and reattached the shield/heatsync but, unfortunately, after 15 minutes it still starts to act up unless I keep a running fan over the vent holes. That being said, where is the best place to find 9918A replacements?
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Last night I was able to get a digital multimeter test the power supply. After spending a lot of time on the Internet trying to find the pinout and voltages and coming across a lot of conflicting information I saw that the voltages were written on the wall wart (see attached pictures). Pins 1 & 2 were 19.77 VAC and 2 & 4 were 8.93 VAC. I am not sure if this is pretty much what I should expect or significantly out of spec. Any wisdom on that point would be much appreciated.
Also, I did run the machine (with a fan on the VDP) for a good while and the 4624N did not get hot. It stayed room temperature the whole time (@HOME AUTOMATION).
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8 hours ago, Lee Stewart said:
Considering that the TI-supplied heatsink is comparatively thin and touches both the chip and the metal shield, I should think a hole would need to be cut in the shield to accommodate the larger heatsinks.
...lee
Yes, that was my thought too.
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33 minutes ago, --- Ω --- said:
Yes, but the best way to eliminate the overheating problem (IMHO) is...
(ducking & running)
I've heard about these. Are they still for sale today?
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40 minutes ago, wierd_w said:
Speaking of which, it looks like the default choice in the late 70s was the white junk. Blech. Put a nice chipset heatsink on there with some silver compound. Will probably get the overheating issue sorted. Another thing to check would be reseating the IC. It could be working harder than it should be, due to poor signal fidelity, and generating heat.
Do you have suggestion(s) on where I could find a good heatsink for the 99? And I am guessing that this would mean somehow removing the existing "heatsync" (rectangular metal slab) attached to the RF shield?
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11 hours ago, HOME AUTOMATION said:
Dragonstomper! I didn't notice, I'd been promoted.
Ooops. I'm new to the forum and it shows. Apologies.
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So I did some more testing tonight. I got rid of the big room fan and fired up Donkey Kong (this game tends to make the issue appear quickly) from my FinalGROMM99. Sure enough, 3 or 4 minutes in the issues started. When it did, I hit the 9918A with a shot of compressed air (not cold air, just compressed for blowing out dust). After a 3 or 4 second burst things went back to normal. They would stay fine for about 30 seconds or so before the sound and / or graphics started to distort again. I would hit it with another spray and things would again immediately stabilize. The system never crashed as long as I did this which was about 7 or 8 times I think.
After that I pulled a heat sync fan from an old PC, wired it up to a power adapter and put that right over the 9918A (see picture) so that it was cooling that and nothing else (not the power supply components). I played Donkey Kong and other games for quite some time and the issues never came back.
At this point, I am again, suspecting the 9918A as the culprit and wondering if just putting thermal compound on it will resolve all the issues. But, I am very troubled by the fact that Dragonstomper is saying that the 9918A should have no problem running without cooling or the heat sync... The last thing I want is to put it all back together have the same issues.
Again, your thoughts are welcomed.
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Thanks everyone for your thoughts. So I ran it bare and played Donkey Kong for like 3 minutes and the issue came back. Then I put a fan (the only one I had handy so don't judge! Hahaha) on it and it ran like a champ without any issue. And had my best game of DK ever!
So does this mean:
A) The chip is good and I should just reapply some quality thermal grease and reassemble?
B) The chip starting to have issues and should be replaced before being reassembled?
Appreciate all the help.
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So after watching some disassembly videos I was able to very carefully disassemble my 99/4a tonight. I was surprised to find a MASSIVE amount of thermal compound on the 9918A. This can't be normal... can it?? I am not sure if this is a sign that someone was being very sloppy the day it was assembled or if someone has been in it before and tried to resolve what they thought was a heat issue with a load of thermal paste. The paste seemed a little rubbery but not completely dried out.... So I can't tell if it was original or not. At any rate it took my 45 minutes of detailed cleaning to get it off the chip, heat sync and board. What a mess!!
The plan from here, I suppose, is to reapply thermal grease, reassemble and see how it behaves. Or, I suppose I could run it bare with a fan on the 9918A and see what happens? Thoughts anyone?
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2 hours ago, Nick99 said:
Is the problem the same without the speech synth?
Yes, the behavior is the same when the speech synthesizer is not connected.
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I was really excited to have acquired a cosmetically excellent TI-99/4A. I was even more happy when it powered up and worked, seemingly, without issue. However, now I've notice that after about 15 minutes or so of game play video distortion and / or graphical errors will start to happen. Shortly thereafter, the sound and / or game play will begin to distort or act crazy. Eventually it will freeze the machine.
If I leave the system off for while and come back later it things will be good for another 15 minutes or so but eventually the behavior always returns. It does this on an original Parsec cartridge as well as a FinalGROM99 cartridge/3D printed case I have. It gets pretty warm on the face of the console just below where the cartridge is inserted. But perhaps this is normal...
After buying the TI, a joystick adapter, speech synthesizer and the FinalGROMM cart it's so disappointing to realize that the TI has a major issue. I really did not want to have to crack it open... sigh. Any suggestions anyone has about how to diagnose and fix this issue are greatly appreciated.
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Just circling back on this issue. Thanks everyone for you responses.
The paddles move smoothly and do not jitter. While the paddles stop in roughly the same place it is not exactly the same place. If I were capable of creating a circuit diagram I definitely would... but then again, if I had that kind of know-how I could probably fix this without any assistance! Haha. I think replacing the capacitors might be a good first step and something I could probably do. I'll just need to figure out what the appropriate modern day replacement should be.
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I've got a Concept 2000 TV+4 Pong clone I purchased from eBay. Amazingly, when I hooked it up to an old LCD that I picked up from a Goodwill (has coaxial in) it worked. However, there is an issue with the "players" only being able to move from the top of the screen to just below the middle. I opened up the the slide controllers and the main unit looking for a pot I could adjust to fix this issue but found nothing. I attached a picture that shows the lowest point the players will go when I have the paddles (or sliders?) all the way at the bottom of their range.
I would greatly appreciate any insight someone may have on how to fix this
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Black screen and the screech of death...
in TI-99/4A Computers
Posted
I've got a 99/4A that when powered on outputs black video sustained screech when turned on. I've seen other post about this same problem and have tried what I believe are all the simple fixes including:
- Checking the power supply (I've tested the voltages and it's confirmed working for two other 99's)
- Removing the cartridge connector
- Reseating all the sockets chips
- Looking for anything on the board that is damaged
I had a spare 9918A and swapping that in but got the same results. I have a logic probe and could run tests (if given VERY specific instructions) but no soldering skills. Thanks in advance for your insights.