InfiniteTape
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Posts posted by InfiniteTape
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Finally got back to the bench. I decided to look closer to the CPU, so I walked through the address lines. Line A8 (CPU pin 16) looks like this at everywhere along its path.
I did pick up another working console last weekend, and this is what A8 should look like.
Pondering my next step. A8 connects to the CPU, RAM, ROM, GROM Port, IO Port, and U509, so plenty of points of failure.
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Well, what I was able to determine last night is that the GROM select is never being pulled down. When I can get back to this on Sunday, I'll start tracing my way back, but it's going to be a learning process through all the logic chips. At least I'm picking up another console on Saturday so I can do comparison testing without disturbing my daily driver.
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16 hours ago, speccery said:
I can look at this in the evening if I have time. I just designed a GROM replacement board which I got properly working yesterday, I will be opening its own thread for that when I have time . My TI is wide open at the moment due to that work, so easy to measure.
I'm not sure your picture displays a bus conflict. If the only activity which was done during the capture on the 8-bit bus is reading of GROMs, this could be ok - need to compare to a working TI though. The GROMs have weak drivers and they leave their outputs floating after the bus cycle is over (i.e. GROM CS goes back high). If nothing else is being read on the 8-bit bus then no device would actively be pushing the signal anywhere. It would be interesting to look at this if you would also include the GROM chip select signal on another channel.
My understanding is that a common failure point are the 4116 video RAM chips, if you have the F18A board you could plug that in to see if it fixes the issue as it incorporates its own VRAM.
I should mention that I did contribute a little to Noel's video by doing some comparison measurements for him. In his case one of the issues was a blown up ROM chip if I recall correctly.
I'm attempting to get that 2 channel shot. It's being finicky. Might need to come at it again tomorrow.
I did swap in an F18A, but I get the "waiting for VDP data" screen, so I don't think I'm getting to the 9918 initialization part of the startup sequence.
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23 hours ago, Ksarul said:
If you pull a copy of the original 99/4 troubleshooting manual from WHT, I believe it has a lot of relevant signals shown in it--even though it was for the 99/4. The troubleshooting tree isn't half bad either. Note, the manual is in two parts.
I'd been using the tree in the 1983 manual, but thanks for the pointer to the 99/4 manual with the signals. In both trees, I get stuck in a loop where it has me remove the groms and sound chip, replace them one-by-one, then loops back to the top of the page. Hmmm...
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Here is U614, 74LS245, pin 9. This is the side that starts at pin 41 of the 9900. It looks like what I expected.
Here is pin 11, which is the output D0 line that goes to the GROMs, sound chip, cartridge port, and expansion port. To me, this looks like what people in YouTube videos call a bus conflict, hence my suspicion of the logic chips leading to the GROMs. However, I haven't dug into one of my working consoles to compare.
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9 minutes ago, GDMike said:
Cool. This would be nice to know what we should be seeing, then I'd be better at using my scope to track down issues on my my machine.
But first I need to identify if my ps is functioning before I do that. I've tried 2 different ps and get different types of black screen. It get a no response on one totally black and a gray on the other...I have to start way back to the PS first, as I'm thinking one of the PS actually killed the MB.
Good luck I'll be watching this.
I'll post some pics of what I'm seeing later tonight. I was suspicious at first of the 5V rail only reading 4.2V, but I tried swapping in a supply outputting 5V and didn't get a change in behavior. I went ahead and ordered some replacement scratchpad RAM chips, but the more I poked around, the less convinced I was that was the problem.
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Inspired by watching too many Adrian and Noel videos, I'm trying my hand at board-level repair of a TI. It's the typical black screen and tone failure mode.
An area I've honed in on is the GROM data bus after the 74LS245. I've removed all the GROMs and the 9918, but when I look at D0 on the output of the 245 and the GROM sockets, I get sloped triangle waves at different amplitudes instead of the square waves on the input side. Has anyone seen this before? Any advice on telling if it's the 245, 373, or 244 that's causing it, or if I'm totally on the wrong track?
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I had something that looked like this. Pretty sure it was Radio Shack brand.
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On 8/30/2022 at 7:12 AM, retroclouds said:
I would buy it! 😀
So would I. I did wonder if, in the spirit of the code article, whether the design techniques could be described in a format like 99er columns. Then we could have a "best of" collection at the end.
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On 8/20/2022 at 7:54 PM, Switch1995 said:
$1780...I know Geneves are rare but jeez...
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Searching around a bit, it sounds like he really didn't release much, but there's some linked in this thread:
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With this setup, you could probably also tie to the FinalGROM's reset buttons, then make yourself a key combo on the remote side to trigger them.
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Pandoc might be able to do it: https://pandoc.org/
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13 hours ago, OLD CS1 said:
A clone is completely different, and it does not seem Taito ever sued Nintendo. It may be a "blatant rip-off." If one were to consider a rip-off or clone as piracy, one could also accuse Texas Instruments of pirating Space Invaders. Even if Nintendo had violated Taito's copyright, similar to the Ms. Pac-Man saga, the fact pattern would bear no resemblance to the GaryOPA situation.
The TI and Nintendo clones pre-dated by several years the Atari vs. Philips case over K.C. Munchkin!'s similarities to Pac-Man, which set the precedent that a clone can copy the expressive concepts in an original work, which violates copyright. It may be that Japanese copyright law didn't give Taito the standing to attempt a suit against Nintendo.
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1 hour ago, jedimatt42 said:
( sorry, this will be off topic.. Glad I didn't check Atariage until now, I wouldn't have expected to find spoilers... I guess no where on the internet is safe on a Sunday )
Sorry, I figured it wouldn't be a big deal three hours after the fact.
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Installed this morning while doing some multitasking. Awesome product, Shift838!!!
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Failing here as well.
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Thanks for all your hard work! I've got my order in.
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22 hours ago, Tursi said:
Post a pic. We should be able to tell
Looks like it's the wait state switch based on the diagrams at http://www.mainbyte.com/ti99/16bit32k/32kconsole_2.html
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16 hours ago, InsaneMultitasker said:
Is it this console speedup modification, by chance? Might go along with the internal (possibly 16-bit) 32K update?
http://www.mainbyte.com/ti99/speedup/speedup.html
I'm thinking it might be something like that. I need to run some more trials, but it does seem a little faster. I ran the Megademo in 7:30 rather than 8:00, so about a 9% speed increase. If anyone has any other good tests, especially those that don't need a working FCTN key, I'd love to try them.
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On 3/9/2022 at 3:55 PM, Switch1995 said:
This poor TI looks like it has been operating a coal mine shaft elevator for 40 years...and then got shipped to a Russian tank.
https://www.ebay.com/itm/133947049546?hash=item1f2fddc64a:g:ukQAAOSwOeFhWi2e
I grabbed this, figuring if nothing else it might have some parts to salvage. While the keyboard needs some work, it turns out that this guy has an internal 32K mod. There's also a small toggle switch on the back. It doesn't disable the 32K, so I'm not sure what it does yet.
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2 hours ago, dhe said:
One thing, I bet you all don't do very often, is sort from highest to lowest?
The 725 one is just a few miles away from me. I've been tempted to make a lowball offer just to see what happens. I think it's been posted for more than a year.
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I lost the inside piece for one console. The next time I get far enough down in my project list, I plan to create models of both pieces for 3d printing. You know...2025.
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Received mine today, and the initial results look promising, even with the PEB extension cable in use. I've currently got it mimicking HAL 9000 on repeat. "Hello Doctor Name Continue Yesterday Tomorrow"
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Trying some board debugging
in TI-99/4A Computers
Posted
@Duewester, glad you're chipping away at it. Life's gotten a bit busy here, so I haven't gotten to spend the in-depth time on investigation that I wanted. I tried installing just GROM 0 from a working TI, but that didn't change behavior. I also tried piggybacking different 6810 chips to see if that might help diagnose a scratchpad ram problem, and that didn't work either. (Both were shots in the dark.)