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linuxfanman

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  • Birthday 09/17/1975

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  1. Looks like a pull up resistor going from pin4 (LP) to +5VB works. At least with the bad ANTIC in the 600XL right now. I'll get a new one ordered here soon for the true fix.
  2. It was so late when I finished last night I really didn't get to test it that much. The graphic glitches are gone now. Which is great, but I can't seem to load my AtariMax 8Mbit flash cart without power cycling a few times. It seems to load to a black screen, the Self Test, or to some random game on the cart. So it's still not right. It will load regular carts just fine. So going with what Rybags said... Yeah I'm not happy with it, I think that's the reason it's having issues loading the flash cart. I'm thinking signaling timing is slightly off on PH2 causing issues loading flash carts. The 600xl loads the flash cart fine. So I put the Sally chip and 74ls08 from the 600XL in the XEGS and it still does the same. So that rules out the Sally chip. Looking through my chip stash now, it doesn't look like I have a 74f08 to swap out right now to see. But I'm thinking that's it. The 600XL buffered PH2 line looks much better then the one produced on the XEGS. Thoughts???
  3. I'll put the good ANTIC back in my 600XL and buy a "new" one. It is a weird failure, only thing I can figure its internally shorted to voltage or signal. When LP goes low (ground) it sends voltage/signal through what ever it's shorted to and to DL during the VBI screwing up the whole thing. Idk. Just my guess. Might explain the "noisy" address and data lines. That disappeared too after the ANTIC replacement.
  4. Well, I de-soldered the ANTIC and put a socket in. I lifted pin 4(LP) which would make it low like the button was pressed permanently and wow, glitchy graphics from the start. So I took the ANTIC out of my 600xl and put the one from the XEGS in it. Now it's producing horrible color (just way off), and the same glitches. Put the ANTIC from the 600XL in the XEGS and bingo, works like new. So it looks like I'm the search for an ANTIC CO21697. Before I head to flea bay, anybody here have one for sale??
  5. @_The Doctor__ Yeah I really need to just make a test rig for Atari 8Bit's like I have for the C64, and few other systems. I really just started getting into Atari 8bit's. So my chip swapping selection is really zilch right now. I have a ton of Amiga, and C64 chips (Denise, Agnus, SID, VICII, etc..) Unless I rip open my 600XL that I just fixed dodgy sockets in... Hmmm 🤣🤣🤣 I'm still waiting for my chip tester (backbit) to come in, which tests all the 8bit chips (along with a ton of other chips). Should I open the 600xl or wait? That's the question... 🤣😉🤣
  6. @Rybags I'll have to de-solder it and put in a socket. But I was thinking the same thing, just lift pin 4 (LP) to see. Yeah the OS passed in Self Test, and SALT tests. But since it handles the display list (I think, could be wrong. I'm still learning the 8bit), along with ANTIC, it's got to be one of them. The LS08 seems to function properly. Logic seems to function as it should according to it's truth table when probing it. PH2/O2 looks good coming out too. Seems to me at least, to have a lot of rippling at the top of the wave in the data and address signals. Here's a video... ANTIC seems to be the warmest, not hot, but warmest chip on the board also... PXL_20240206_005122538.mp4
  7. Here's some videos of what it's doing. It does the same thing when you load a cart. Once you hit the fire button, it glitches. Not sure if it does it on tape or disk based games as I have no disk or tape drives for Atari 8bits. But I'm sure it would. PXL_20240205_234154132.mp4 PXL_20240205_233739668.mp4
  8. @_The Doctor__ I've tried multiple joysticks, Atari, Jem, Wlco, other 3rd party all known good, all with the same issue. I've traced the line back from the port to the GTIA and the 74LS08, R69, R63, L27, L25, (no shorts, values good) all seems fine. It replicates the issue with the keyboard connected or not. Powered by my bench supply at 5 volts. Reads 4.97v at the controller ports, GTIA and ANTIC. Address lines and data lines do look noisy though. Clock signals looks good, no noise.
  9. Hello all, I just wanted to get some input from everybody before I dive into this repair. I have a XEGS I just purchased (not working) that is doing some weird stuff. It will boot fine into Basic, Missile Command, Self Test. I can run the self test, Salt and super salt with no errors. However, it starts having issues as soon as you press the fire button on the controller, (port 1 and 2). In Missile Command, it will make the all the background graphics jump around on the screen making the game unplayable. However, sprites and color are not messed up. Sprites are located where they should be without glitching. If you run self test and press a joystick button during it, it makes the text disappear and re-appear, over and over again randomly. If I run a cart like pole position, which you can play without pressing the fire button, it works perfect until you hit fire, and then the games graphics glitch with a bunch of garbage on screen and crashes the whole computer. Seeing that the sprites and color are working ok, I'm ruling out GTIA. I'm thinking it's the ANTIC chip, when you press the joystick button it makes the LP signal go low which it should coming off the trigger lines from GTIA, and going through the 74LS08 AND Gate. I think it has something to do with the VBI (Vertical Blank Interrupt) and when writes to the DLI (Display List Interrupt) in shadow ram $2XX, something is going haywire. The LP signal gets written to the shadow ram at next VBI, that's where I think the problem lies, like it's corrupting the DLI at that time. If pictures or video is needed I can upload some. But could this be caused by the system OS? Any thoughts???
  10. @Paul Westphal Thanks for the advise. I checked and I have signal there. But not sure if the delay frequency is right. But through further troubleshooting I found bad sockets to be the culprit. One being U7. The socket is causing a floating ground on that chip. Which entail, buffers the CASINHIBIT signal from the MMU going into the delay line IC which is fundamental to creating the correct CAS signal timing going to the RAM. I'm actually happy that the computer died. It's made me learn about how the 8-bit works. But I still have a lot more to learn. 😉
  11. @Rybags After I saw your what you said above, it dawned on me that GTIA is kicking in with U7 being grounded properly, but not even trying to boot the OS/Basic, the system goes into HALT. When I got home from work I started checking other sockets and found pin 13, the PIA line, of U1, the memory decoder, was not making good contact either to going to PIA. So with out PIA mapped in memory, yeah the system wont boot. Now I'm going to have to check every trace from every chip I pulled because these sockets suck. Like one time use I guess. lol.. Is this common with Atari 8-bits, bad sockets?? Amiga's and C64's are notorious for that. Probably anything with sockets from the 80's. LMFAO
  12. Alright, I think I may have found the issue, but I won't know until parts come in. Before I de-soldered anything else off the XEGS, I decided to poke around the board some more. I found that U7 the 74LS08 was acting wonky. Pin 7 is ground, but I found it floating. So I pushed a bit with the tip of my multimeter probe and it contacted solid ground. I took the chip back out and de-oxited the socket again, and re-seated the chip. Nope. Same thing floating ground on the scope. So I pulled the chip up a bit so pin 7 had good contact, other pins did not. But I tried it, and I got a brownish screen. So I'm thinking this is it. This is the chip that works in conjunction with the delay to created the ras and cas signals. Plus the other pins on the chip work with other timing signals for Sally, Anitic, and GTIA. I'm beginning to see how picky the 8-bit is with timing, assuming because of the parallel bus. But I'm all out of sockets to try it now. Fingers crossed when they come in.
  13. Nope, the CPU from the XEGS doesn't boot the 600xl either. But I did scope out LUM0 through LUM3, and CSYNC on GTIA and am getting nothing out of them. Stuck Low. Hmm. Symptom of something else, or a bad chip...
  14. @xrbrevin No, I meant swapping the CPU's above. I just got my XEGS to work, replaced the MMU with one I burned on with the XEGS MMU Code to get it running.
  15. @flashjazzcat I'm in the process of de-soldering the Sally from the XEGS (which I just got working MMU, 74LS138 memory decoder issues on that one). I'll report back once I swap them. I just hate de-soldering on the XEGS though, delicate via's/traces. Really a testament to the Tramiel Era of cheapness compared to how well built the 600xl is. Wish I had a Syscheck II. Might get one after this fiasco. I don't get any Atari's in to fix, mainly Apple's and Commodore's. But this is my personal Atari. It's just driving me nuts I can't figure it out. If it was an Amiga it would have been fixed already. LOL Is this flashjzzcat from YouTube?? If so, thanks for all the videos, I've been watching them trying figure this out. If you want check out my channel. https://www.youtube.com/retrogamergenx I mainly do retro video game console and vintage computer history videos, but I also have a play list for repairs and mods. I have a video I did over a decade ago on my old channel that I reposted on this one doing the 600xl 64K mod. That's last time I worked on an Atari 8-bit, and before I had all my equipment.
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