lgallair Posted October 12, 2020 Share Posted October 12, 2020 A TI 99/4A QI computer recently came into my possession but sadly it has video RAM issues. According to this website, the issue is bit 5 is stuck at 0 because that screen shot is exactly the same screen I get. My problem is I do not know which chip to replace. The diagram shows the chip locations for a non-QI model. Does anyone know which 4116 chip represents the bit 5 circuit on a QI board layout? Quote Link to comment Share on other sites More sharing options...
+arcadeshopper Posted October 12, 2020 Share Posted October 12, 2020 11 minutes ago, lgallair said: A TI 99/4A QI computer recently came into my possession but sadly it has video RAM issues. According to this website, the issue is bit 5 is stuck at 0 because that screen shot is exactly the same screen I get. My problem is I do not know which chip to replace. The diagram shows the chip locations for a non-QI model. Does anyone know which 4116 chip represents the bit 5 circuit on a QI board layout? From the same page (below the examples) shows which bit is which chip. to test the theory try piggybacking a good chip on top of the old one https://www.ninerpedia.org/wiki/File:Vram.jpg The image shows the bit numbers on the circuits. Note that Texas Instruments uses a big-endian bit order, i.e. bit 0 is the most significant bit (27), and bit 7 is the least significant bit (20). Accordingly, if your failure symptom is Mask 11011111, this means bit 2 is stuck at 0. 1 Quote Link to comment Share on other sites More sharing options...
+mizapf Posted October 12, 2020 Share Posted October 12, 2020 Note that he refers to a QI board. Quote Link to comment Share on other sites More sharing options...
+arcadeshopper Posted October 12, 2020 Share Posted October 12, 2020 Yeah I noticed but shouldn't it be the same bits just in a vertical line? Or do you think ti rekajiggered the ram locations tooSent from my LM-V600 using Tapatalk Quote Link to comment Share on other sites More sharing options...
Ed in SoDak Posted October 12, 2020 Share Posted October 12, 2020 (edited) I suppose you could meter the datalines from brain to RAM for continuity on bit 2. But that might require chip pinouts and/or schematic. Edited October 12, 2020 by Ed in SoDak 1 Quote Link to comment Share on other sites More sharing options...
Stuart Posted October 12, 2020 Share Posted October 12, 2020 54 minutes ago, arcadeshopper said: Yeah I noticed but shouldn't it be the same bits just in a vertical line? Or do you think ti rekajiggered the ram locations too The 9918 has been rotated 180 degrees on the QI board, so anything might have happened ... 1 Quote Link to comment Share on other sites More sharing options...
HOME AUTOMATION Posted October 12, 2020 Share Posted October 12, 2020 Yes, changed! Now (more correctly) in respective order. D0=U9 ram IC located closest to the video port. . . . . . . D7=U16 ram IC located closest to keyboard connector. 1 Quote Link to comment Share on other sites More sharing options...
Ed in SoDak Posted October 12, 2020 Share Posted October 12, 2020 Hokay, for what it's worth! Here's a clip of the 99/4A schematic and board layout, with RD line 2 called out. It goes from pin 30 of U100 (TMS9918) to pin 14 of U106 (4116 RAM). Seems to agree with the pic blaming the 5th 4116 from the left as the faulty chip. So, just trace out pin 30 on the QI's 9918 to whichever 4116 it leads to. Stick one DMM probe to 9918 pin 30 and check each 4116's pin 14 in turn. Only one chip should have continuity. I leave it to you to figure out which pins those are. Aw, heck, I looked that info up too. I don't have a QI schem or layout, which would have made it all much easier! 3 Quote Link to comment Share on other sites More sharing options...
Ed in SoDak Posted October 12, 2020 Share Posted October 12, 2020 (edited) 1 hour ago, HOME AUTOMATION said: Yes, changed! Now (more correctly) in respective order. D0=U9 ram IC located closest to the video port. . . . . . . D7=U16 ram IC located closest to keyboard connector. U11 for the win! All we need now is the board pic called out like on Ninerpedia. Edit: Or is that too obvious? Edited October 12, 2020 by Ed in SoDak Quote Link to comment Share on other sites More sharing options...
HOME AUTOMATION Posted October 13, 2020 Share Posted October 13, 2020 40 minutes ago, Ed in SoDak said: U11 for the win! All we need now is the board pic called out like on Ninerpedia. Edit: Or is that too obvious? Well, U asked for it! But my camera Scks. Don't have a board to photograph either. 2 Quote Link to comment Share on other sites More sharing options...
Ed in SoDak Posted October 13, 2020 Share Posted October 13, 2020 Thanks Homey! lgallair oughta be able to figure it out from here. Quote Link to comment Share on other sites More sharing options...
+dhe Posted October 13, 2020 Share Posted October 13, 2020 If you are going to fix RAM, may as well do the upgrade! 1 Quote Link to comment Share on other sites More sharing options...
HOME AUTOMATION Posted October 14, 2020 Share Posted October 14, 2020 2 hours ago, Ed in SoDak said: Thanks Homey! Hmm, Your TI-99/4A parts placement diagram differs from the one in my book somewhat. Particularly around the VDP XTAL. Here's another copy of the book I'm using... https://archive.org/details/TI994AConsoleAndPeripheralExpansionSystemTechnicalData/page/n17/mode/2up I didn't know we were HOMEIES! ...much Love. Quote Link to comment Share on other sites More sharing options...
HOME AUTOMATION Posted October 16, 2020 Share Posted October 16, 2020 Hmm, reviewing this thread in it's totality... @lgallair, most likely did review this page --https://www.ninerpedia.org/wiki/Troubleshooting--. In which case, it's fair to assume he is correct in diagnosing bit 5 as the culprit.(not bit 2). So, in contradiction to our previous posts. The following would be correct... Quote Link to comment Share on other sites More sharing options...
+mizapf Posted October 16, 2020 Share Posted October 16, 2020 If someone could do a good photograph of a QI board, we can add that to Ninerpedia with the appropriate chip numbering. 1 Quote Link to comment Share on other sites More sharing options...
RickyDean Posted October 16, 2020 Share Posted October 16, 2020 (edited) 3 hours ago, mizapf said: If someone could do a good photograph of a QI board, we can add that to Ninerpedia with the appropriate chip numbering. I have a few more days till my Vaca is over, if no one had posted one by then, I have a Q1 already out of the case (non working), I can take a photo or two then. Monday or Tuesday. Edited October 16, 2020 by RickyDean spelling Quote Link to comment Share on other sites More sharing options...
HOME AUTOMATION Posted October 16, 2020 Share Posted October 16, 2020 This post contains a decent pic... ..not sure about it's terms though! Quote Link to comment Share on other sites More sharing options...
RickyDean Posted October 16, 2020 Share Posted October 16, 2020 2 hours ago, HOME AUTOMATION said: This post contains a decent pic... ..not sure about it's terms though! Looks as good as any I'd take, should be sufficient. Quote Link to comment Share on other sites More sharing options...
lgallair Posted October 18, 2020 Author Share Posted October 18, 2020 Thanks for all the help guys. I recently upgraded the RAM in my Joust cocktail with 4146 so I have a bunch of 4116 RAM's to try. Was going to piggy back onto the offending RAM chip when all of a sudden, the power board went "poof" before I could even try. After the little tiny puff of smoke dissipated, I could not identify what exactly blew. I'm guessing an electrolytic cap. There is a small burn mark on the white wire which goes to the two-pin power connector. So I'm off to Digi-Key for some caps and am going to re-cap all 10 or 11 caps on the power board. Now I have at least two problems with the TI-99. Sheesh! 2 Quote Link to comment Share on other sites More sharing options...
lgallair Posted October 29, 2020 Author Share Posted October 29, 2020 I recapped the power supply and now the power on all rails is good except for the -5V rail. It's fluctuating around -3.3v to -3.5v. I'm not sure how to get the voltage within spec. There's a variable pot but adjusting that seems to only change the +5v rail. I had a PC power supply sitting around with the proper voltages (+5v, +12v, and -5v) so I hooked it up to the motherboard. It booted up to the same screen as before. I piggy-backed a 4116 RAM chip on each 4116 chip on the board in succession and determined the faulty chip. I de-soldered it and replaced with a socketed ram chip. I'm so happy the blown cap didn't damage the main pcb. 4 Quote Link to comment Share on other sites More sharing options...
Ed in SoDak Posted October 29, 2020 Share Posted October 29, 2020 3 Quote Link to comment Share on other sites More sharing options...
Keneg Posted October 30, 2020 Share Posted October 30, 2020 On 10/28/2020 at 10:05 PM, lgallair said: I recapped the power supply and now the power on all rails is good except for the -5V rail. It's fluctuating around -3.3v to -3.5v. I'm not sure how to get the voltage within spec. There's a variable pot but adjusting that seems to only change the +5v rail. I had a PC power supply sitting around with the proper voltages (+5v, +12v, and -5v) so I hooked it up to the motherboard. It booted up to the same screen as before. I piggy-backed a 4116 RAM chip on each 4116 chip on the board in succession and determined the faulty chip. I de-soldered it and replaced with a socketed ram chip. I'm so happy the blown cap didn't damage the main pcb. Check the 7905 regulator voltages in and out. If the input is good, I think -8 or less and the output is bad, it is likely the regulator. If the input is bad, you need to check components before it. 1 Quote Link to comment Share on other sites More sharing options...
lgallair Posted October 30, 2020 Author Share Posted October 30, 2020 The QI power supply does not have a 7905 but there is an A1012 regulator. I tested it with a DMM and found the input voltage the same as the output voltage. I have a replacement on order. Will see if that works. Thanks. Quote Link to comment Share on other sites More sharing options...
pnevmati Posted July 2, 2021 Share Posted July 2, 2021 I know this is off-topic but please allow me piggy-back on an active thread: I salvaged a TI99 4A/QI from being thrown to the garbage, and I am about to refurbish it, but I miss the transformer. Unfortunately, I cannot find the exact voltage or the schematic for the QI power supply. From what I read I believe it is 16V AC. Anyone with either knowledge or pointers on how to proceed? Can one measure the voltage on the AC adapter? Many thanks! Quote Link to comment Share on other sites More sharing options...
+arcadeshopper Posted July 2, 2021 Share Posted July 2, 2021 I know this is off-topic but please allow me piggy-back on an active thread: I salvaged a TI99 4A/QI from being thrown to the garbage, and I am about to refurbish it, but I miss the transformer. Unfortunately, I cannot find the exact voltage or the schematic for the QI power supply. From what I read I believe it is 16V AC. Anyone with either knowledge or pointers on how to proceed? Can one measure the voltage on the AC adapter? Many thanks!The qi supply works with the original transformer. It only uses one of the 2 ac power connections the 16vac one http://www.mainbyte.com/ti99/hardware/power_supply.htmlSent from my LM-V600 using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
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