StephenM Posted August 14, 2020 Share Posted August 14, 2020 Hi, This is my first TI99/4a repair and have been trying to find a solution in this forum but cannot find one. Initially I had screen corruption and found that one of the 4116 RAM had failed. As in the first pic. Success, a nice simple repair but after trying it again the screen slowly corrupts after about 20 seconds. First it starts nicely then a pixel disappears from the hyphen and then characters and different coloured blocks appear in the lower third of the screen. I tried it with a cartridge and the game works, but as before, it starts to fail graphically. Any ideas? Screen image is a bit poor as it needs a composite modification as the original modulator needs grounding properly. Best regards StephenM Quote Link to comment Share on other sites More sharing options...
AwkwardPotato Posted August 14, 2020 Share Posted August 14, 2020 Make sure the voltages coming off the internal power supply are staying in spec as the machine warms up. If they are, chances are the VDP needs to be replaced (or one of the 4116s is behaving intermittently, but that's unlikely). Quote Link to comment Share on other sites More sharing options...
StephenM Posted August 14, 2020 Author Share Posted August 14, 2020 Cheers, will do. Is the VDP chip widely available or will it need this new fangled F18 replacement that I'm reading about? Quote Link to comment Share on other sites More sharing options...
HOME AUTOMATION Posted August 14, 2020 Share Posted August 14, 2020 Did you review this? www.ninerpedia.org...Troubleshooting 1 Quote Link to comment Share on other sites More sharing options...
StephenM Posted August 14, 2020 Author Share Posted August 14, 2020 Just now, HOME AUTOMATION said: Did you review this? www.ninerpedia.org...Troubleshooting Yes I did, which led me to replacing one of the 4116 RAM. The issue manifests itself after 20 seconds which is a bit weird. Quote Link to comment Share on other sites More sharing options...
HOME AUTOMATION Posted August 14, 2020 Share Posted August 14, 2020 Maybe the VDP is getting too hot... some run hotter than others... need adequate cooling. Quote Link to comment Share on other sites More sharing options...
+Lee Stewart Posted August 14, 2020 Share Posted August 14, 2020 24 minutes ago, StephenM said: Cheers, will do. Is the VDP chip widely available or will it need this new fangled F18 replacement that I'm reading about? TMS9918A VDPs are available on EBay for $4 and up. ...lee Quote Link to comment Share on other sites More sharing options...
+retroclouds Posted August 14, 2020 Share Posted August 14, 2020 looks like bad vram to me. 2 Quote Link to comment Share on other sites More sharing options...
StephenM Posted August 14, 2020 Author Share Posted August 14, 2020 1 hour ago, HOME AUTOMATION said: Maybe the VDP is getting too hot... some run hotter than others... need adequate cooling. I do have the whole board out of its case for testing so no heatsink at the moment. Quote Link to comment Share on other sites More sharing options...
HOME AUTOMATION Posted August 14, 2020 Share Posted August 14, 2020 If you can burn your finger ...that's definitely a bad sign. Quote Link to comment Share on other sites More sharing options...
StephenM Posted August 14, 2020 Author Share Posted August 14, 2020 9 minutes ago, HOME AUTOMATION said: If you can burn your finger ...that's definitely a bad sign. I could cook my dinner on it, it's that hot. So I'll get a new VDP and post the results when I receive it. Cheers Quote Link to comment Share on other sites More sharing options...
HOME AUTOMATION Posted August 14, 2020 Share Posted August 14, 2020 well, some of them do get rather hot... my first sure did! Some cages have a heat-sink built in. So, might still be ok. Quote Link to comment Share on other sites More sharing options...
HOME AUTOMATION Posted August 15, 2020 Share Posted August 15, 2020 Quote Link to comment Share on other sites More sharing options...
GDMike Posted August 16, 2020 Share Posted August 16, 2020 (edited) I ordered an 9918a from eBay and it worked in my system that had faded coloring, and applied new thermal grease - that chip lasted 15 minutes and croaked. At least with the old chip I can still use the computer. Scared to buy another from eBay even though mine said tested, from Arizona but chips were from China the seller said, but no TI logo either. A test needs to be longer than 5 minutes. Edited August 16, 2020 by GDMike Quote Link to comment Share on other sites More sharing options...
StephenM Posted August 17, 2020 Author Share Posted August 17, 2020 10 hours ago, GDMike said: I ordered an 9918a from eBay and it worked in my system that had faded coloring, and applied new thermal grease - that chip lasted 15 minutes and croaked. At least with the old chip I can still use the computer. Scared to buy another from eBay even though mine said tested, from Arizona but chips were from China the seller said, but no TI logo either. A test needs to be longer than 5 minutes. Definitely need to be stress tested for a couple of hours. My system boots perfectly but something is going wrong when it warms up. I'll need the PAL version for mine. Quote Link to comment Share on other sites More sharing options...
Stuart Posted August 17, 2020 Share Posted August 17, 2020 Stephen - where in the world are you? Is it a TMS9929 you need? Quote Link to comment Share on other sites More sharing options...
StephenM Posted August 17, 2020 Author Share Posted August 17, 2020 2 minutes ago, Stuart said: Stephen - where in the world are you? Is it a TMS9929 you need? I'm in the UK. I've ordered a couple from different sources, alas China, so it will be a while before they arrive. Fingers crossed that are what they say on top of the chip. Quote Link to comment Share on other sites More sharing options...
Stuart Posted August 17, 2020 Share Posted August 17, 2020 11 minutes ago, StephenM said: I'm in the UK. I've ordered a couple from different sources, alas China, so it will be a while before they arrive. Fingers crossed that are what they say on top of the chip. I've got some 9929's here looking for a new home. If you want a couple, PM me your address and I'll pop them in the post. 2 Quote Link to comment Share on other sites More sharing options...
StephenM Posted August 17, 2020 Author Share Posted August 17, 2020 37 minutes ago, Stuart said: I've got some 9929's here looking for a new home. If you want a couple, PM me your address and I'll pop them in the post. Cheers Stuart. Quote Link to comment Share on other sites More sharing options...
Like us on Facebook
Follow us on Twitter
AtariAge on Instagram
Watch us on YouTube
Chat on Discord
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.