ti99iuc Posted July 10, 2019 Share Posted July 10, 2019 Hello, a 99er friend on Facebook has this issue on a TI-99/4A so i checked screens on ninerpedia https://www.ninerpedia.org/wiki/Troubleshooting to check if this issue is recognizable but i can't see a matching... Maybe it could be more of one chip broken to show this issue? or maybe another thing... Any Idea and help please? Quote Link to comment Share on other sites More sharing options...
iliketurtles Posted July 10, 2019 Share Posted July 10, 2019 Are those stripes showing up in the color bars or are they just an artifact of the picture? Quote Link to comment Share on other sites More sharing options...
ti99iuc Posted July 10, 2019 Author Share Posted July 10, 2019 Stripes, sure Quote Link to comment Share on other sites More sharing options...
GDMike Posted July 10, 2019 Share Posted July 10, 2019 Looks like bad ram..anyone else chime in Quote Link to comment Share on other sites More sharing options...
AwkwardPotato Posted July 10, 2019 Share Posted July 10, 2019 This one is weird; normally when one of the VRAMs fails, the corresponding bit just gets stuck and garbles the entire screen. It could be the VRAM at U104 seeing the random ' " ' characters, otherwise I'd suspect the VDP. 1 Quote Link to comment Share on other sites More sharing options...
ti99iuc Posted July 10, 2019 Author Share Posted July 10, 2019 (edited) ok thanks for the suggestions guys. Edited July 10, 2019 by ti99iuc Quote Link to comment Share on other sites More sharing options...
+FarmerPotato Posted July 10, 2019 Share Posted July 10, 2019 11 hours ago, GDMike said: Looks like bad ram..anyone else chime in TLDR; still points to what others have concluded, one bad VRAM chip, bit number 6. This is fascinating.. only three spaces >20 are transformed into quotes >22, each time in column >09. (but not column >19) Characters A and 1 have a bit set at VDP address >989 and >A09. Other letters in this sequence would be ! and Q, which we don't get to see. Inside the TI logo chars, >809 is normally set. >849 is also inside the TI logo and NOT set normally or in the picture. >889 and >8c9 are not used. Then Color bars.. they are all clear and background color, foreground transparent. Characters >60 to >D8 are the color bars. They must have the >02 bit set consistently in VDP memory in at least >B00 - >B07, from >B40 to >B47 and so on upwards through >E47. (pattern descriptor table. .) VDP RAM above that first 4K is unused by the title screen. 3 Quote Link to comment Share on other sites More sharing options...
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