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DuaneAL

Expansion bus issue

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I recently bought a lot of 5 99 4A's on Ebay that all had issues.So far, i've gotten 3 running. Two are perfect as far as i can see- they see the FinalGROM and the 32k sidecar(shorty from Arcadeshopper) with no problem and I can run all the FG programs that don't require F18A. The Third unit boots up fine with no FG or 32k sidecart and with the FG but no 32k sidecar, but if I include the side car, it boots to a loud noise and a black screen. Any ideas on what I should look at?

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I recently bought a lot of 5 99 4A's on Ebay that all had issues.So far, i've gotten 3 running. Two are perfect as far as i can see- they see the FinalGROM and the 32k sidecar(shorty from Arcadeshopper) with no problem and I can run all the FG programs that don't require F18A. The Third unit boots up fine with no FG or 32k sidecart and with the FG but no 32k sidecar, but if I include the side car, it boots to a loud noise and a black screen. Any ideas on what I should look at?

Are you using external ps?

 

Sent from my LG-H872 using Tapatalk

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Are you using external ps?

 

Sent from my LG-H872 using Tapatalk

No. I am also not going through the Speech Synth. The card works well on the other two as well. I haven't tried the SS to see if it provokes the same response. hold on, i'll go try it now. No problem with the SS plugged in. With the 32k plugged into the SS, boot was fine as well. Then I tried just the side car and got the noise and black screen again. I'll look to see if I have a PS that will work with it.

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Check the metal fingers in the side port. They may be shorting something out, as the symptom points directly to that problem. If it works fine with a Speech Synth, that tells me the metal flanges are protecting everything. If it fails without it, the fingers are probably in contact with a few of the pins in the 44-pin connector. . .and you get the black screen. I see you already found the issue though--and since the Synth doesn't push power across, that too would help avoid the problem of it doing strange things on the bus.

Edited by Ksarul

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Never mind- I found the switch for "ti/ext". That fixed it. Never would have looked if you hadn't asked about the power. I wonder why it works on the other three?

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Check the metal fingers in the side port. They may be shorting something out, as the symptom points directly to that problem. If it works fine with a Speech Synth, that tells me the metal flanfes are protecting everything. If it fails without it, the fingers are probably in contact with a few of the pins in the 44-pin connector. . .and you get the black screen.

Thanks for the response Ksarul! I figured out that my 32k was switched to external and was posting that when you responded. Would the switch make the 32k board act like shorted pins in the ext position with no power?

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Some ti's leak enough voltage to power the 32k some don't. It's strange but usually the prob is the switch/jumper on ext as you found

 

Sent from my LG-H872 using Tapatalk

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I forgot to say that with this fix, I'm up to four good TI'sand have have high hopes of fixing 2 of the remaining 3 bad ones. I bought two back in January and one was bad and the other was a QI so my FinalGROM wouldn't work. SO, I took a chance and bought 5 non-working units from everyones favorite e-bay seller in Colorado Springs. They turned out to be better than I expected, got here quickly and safely (well packed) and probably only cost a little more than they should have ($75 including shipping). Unfortunately, no power bricks- any ideas where I can score 3 or 4 of those?

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I found the "QI" motherboards do not care if an attached device is powered improperly. Specifically the 32k and nanoPEB un-powered will still allow the "QI" console to start up. At least the nanoPEB is not available to the console in this configuration, but I have not tried the 32k.

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I found the "QI" motherboards do not care if an attached device is powered improperly. Specifically the 32k and nanoPEB un-powered will still allow the "QI" console to start up. At least the nanoPEB is not available to the console in this configuration, but I have not tried the 32k.

Interesting! Chipwise, how different is the QI from the original board? So far, I've noticed differences between the two types that affects the FinalGROM and the unpowered 32k(sometimes), so I suppose that the cartridge port and the expansion port are both treated differently by the Q? Did I see that the 99/8 also couldn't use the FG? Timing Issues?

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Specifically, I am not the one to ask. I do know the reduced chip-count was thanks to integration of a number of the TTL logic chips into a large IC, much akin to the conglomeration of logic in a Commodore 64 PLA.

 

The CRU signals are missing from the cartridge port, and it has been discussed another signal is missing, but I cannot recall off the top of my head.

 

You can tell the difference between boards without opening the case by looking at the color of the grounding fingers in the expansion port. Brass-colored fingers are the standard board while aluminum/silver-like colored are of the "QI" board.

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Interesting! Chipwise, how different is the QI from the original board? So far, I've noticed differences between the two types that affects the FinalGROM and the unpowered 32k(sometimes), so I suppose that the cartridge port and the expansion port are both treated differently by the Q? Did I see that the 99/8 also couldn't use the FG? Timing Issues?

Not sure if you've found the Mainbyte resource yet, but if you don't feel like opening one each of yours up side by side to study the differences, there's a lot of information there and some really great, clear photos throughout the discussion.

http://www.mainbyte.com/ti99/computers/ti99qi.html

post-48993-0-50267000-1525494969_thumb.jpg

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Thanks, Helocast I had seen those- They are a great resource! I guess my real question was about signals and timing. I am a mechanical engineer,so the only thing I know about this electrical stuff is to try to keep the smoke in the little wires. Right now I'm up to five of my seven 4A's working. I have one QI and four silver non-QI's functional. I have two non-QI's, one biege and one silver, that beep with a continuous tone and present no video signal. They have different sounds. One has a deep sound at start that changes if you turn the computer on and off quickly. the other has a high pitched sound that stays constant when you turn on and off. I have swapped out the groms, video chips, and the sound chips between the two. I have not tried to swap chips from one of the good boards yet.

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