prorok

Debugging continues... I purchased another 7800. This one appears to be entirely stock, though I haven't opened it up yet to verify, and PETSCII Robots runs just fine on it. With one working and one non-working console, as time permits, I can start running increasingly invasive experiments to see if the problem moves with component swaps.

Thanks, Mitch. The embarrassing truth is that I even have the manual for Tower Toppler. Maybe I should actually read it some time! 🙂

The debug continues... While cycling through my Atari games today, I observed odd behavior with BOTH copies of Tower Toppler I have. I can put in the game and I can select 1 player or 2 player and sound on/off on the main menu. If I choose a 1 player or 2 player game with sound on, both cartridges have the same off behavior that they load the level and after the frog is ready to move on the platform, the level ends and progresses to the next level. This proceeds all the way through all the levels so that it cycles back to the first level. Interesting stuff. I have also taken the big step to figure out this mystery by procuring a second (purportedly working and stock) Atari 7800. It has arrived, but I haven't plugged it in to start more testing of the now two bizarre games: PETSCII and Tower Toppler. I foresee lots of desoldering, soldering and chip swapping in my future while I hunt for the problem.

Okay, more "newbie" questions from a guy who has been playing on a 7800 since the 90's... Is there an establish approach to 7800 debugging? I'm approaching the point where I'll start collecting all the IC's, socket EVERY DIP package on the board and just start swapping parts until I find some love. It would be cool if there were some diagnostics I could run that would exercise the CPU, MARIA, TIA, RAM, etc, so I wasn't just randomly swapping parts with the precision of a shotgun blast. I seem to recall there's some Uber-rare official 7800 diagnostics cart that is essentially unobtanium. Has someone developed a Homebrew test suite either on its own cart or that can be loaded on a Game Drive? Thanks for the guidance. And if you're still reading the thread, Al, let me know when time's up and you want me to send one of the two PETSCII carts back to you. I'm pretty sure it's not the cart's fault, but I'm happy to hold on to them until this problem is solved if you're cool with that.

Did a little more testing today to see if I have problems when any other games and just started walking through my collection in alphabetical order. Everything works in a way that doesn't affect gameplay, but I was being hyper sensitive to glitches that normally I'd just shrug off as artifacts of playing 8-bit hardware on a CRT. Asteroids: seems to work fine without any glitches Ballblazer: there's a brief flash of static between the Lucasfilm title screen and the Ballblazer menu select. The music at some points seems to stutter when it loops Choplifter: a few pixels here or there are glitchy Dig Dug: similarly, a few glitchy / glittery pixels here and there on the screen Again, I guess I'd have categorized all of this as normal, but maybe not. The image is all composite video out with a UAV mod running to a Sony Trinitron TV that could use a tune up. All of this seem normal or does it clue into where to look for the "hard fails" of PETSCII Robots?

Yes, this is the only game I've noticed a problem on. However, I generally play my 2600 games on the 2600 and only own about two dozen pretty common 7800 games, of which I play a minority. PETSCII is my first Homebrew and, in an effort to see if a "challenging" cart might be the problem, just procure Ballblazer this week as a test. Any suggestions for specific titles to try to see if I can repro the problem on anything else? In the meantime, I guess it's time to source a new RIOT and a socket for it. Any suggestions on good sources for that? Dan

Even though people call the Sally chip a 6502C, my understanding is that a real 6502C is something different, a 6502 that runs at 4 MHz. The Atari 7800 uses the same custom Atari C014806 "Sally" 6502 variant used in the 5200 and the 8-bit Atari computers. You can see the C014806 markings in the picture I posted earlier in the thread.

Sprayed some Deoxit in the cart slot and took a look at the cart slot solder joints...all looks okay to my eye. Alas, still not working.

Tried another experiment since everything on my 5200 is socketed in. I swapped the CPU from the 5200 into the 7800, but unfortunately, no change to the 7800 behavior. At least I know that older 6502 is fine. Probably should have tried this long ago, but I have a fresh can of Deoxit to try on the cart port and I will take a careful look at the cart slot solder joints.

Maybe, or it could have been done later. I purchased the system with several mods to have all the bells and whistles: UAV S-video out, blue power LED, recapped with new power regulator, and a normal barrel connector for the power supply. It's possible that as part of the Cadillac refurbishment treatment, it got sockets added for the MARIA and the 6502.

Yes, Al has sent me a replacement and it performs consistently with the original cart. I just tested the replacement cart with the timing circuit disabled and the bad behavior is still the same. Yes, only the MARIA and the 6502 are socketed. Dan

Thanks for reiterating the suggestion to go exploring for the timing circuit. It appears mine was intact: C64 was in place. I went ahead and desoldered one leg and lifted up, but, alas, PETSCII is no different...same AA logo corruption on first screen and crash thereafter. Meanwhile, there's nothing on the bottom of the board in the vicinity of the 6502. The only thing on the top of the board in the vicinity of the 6502 is a yellowy-orange thing jumpered across two pins of the MARIA chip. Any thoughts on next steps? Thanks for your help so far!

Well, I've run the next rounds of experiments and not much closer to getting PETSCII running yet. EXPERIMENT 1: I plugged in the over-spec'd 2500 mA power supply and PETSCII Robots fails in the same consistent way after the first screen. EXPERIMENT 2: I completed a significant "Rite of Passage" and successfully placed and received my first-ever order from Bradley at Best Electronics. Included in that order was my lifetime maximum of ONE POKEY chip: a sealed box copy of Ballblazer. Given all my Atari stuff as a kid came second, third, or fourth hand from garage sales, this was the first time in my life I had a brand new Atari game box I could tear the shrink-wrap off of. Plugged in Ballblazer, played a few rounds, and it appears to work just fine, complete with the groovy music. I had been operating from a theory that maybe the 7800 wasn't getting the power it needed to run the extra HW on the PETSCII carts. That's why I went with a beefier power supply and another title that has extra HW and extra current draw. If I want to keep beating down the power supply theory, I could take a stern look at the internal voltage regulator, but I'm starting to doubt this is the problem since I'd think the problem would be more intermittent, vary with temperature or playing time or something...and why would it have anything to do with the corruption of the Atari Age logo on the initial screen? Nevertheless, I'm getting ready to open up my 7800 and start probing the regulator. In the meantime, is there anything else I should take a look at while I'm inside? Dan

Thanks, CrossBow, for suggestions on next steps. My first guess is that my so-called 1A power supply isn't actually putting out up to 1A, or its slew rate is so slow, it's not ramping up fast enough for a rising current draw. If problems continue after I try the overkill power supply, you make a good point that the voltage regulator is the next piece that take a good look at. To some extent, solving this mystery is at least as much fun as playing the games themselves. We'll solve this puzzle eventually. Dan

Update for those following along at home... Al was kind enough to send me another cart and, unfortunately, it fails in exactly the same way, including the logo corruption. Obviously, my attention is now very focused on my console. I'm now giving a stern look at my power supply. My 7800 is modded to accept a standard 2.1mm x 5.5mm barrel connector and I'm using whatever (supposedly) 9VDC / 1A power supply the modder sent to me when I purchased the console some years ago. While I have never had problems with other carts, I have no other home-brews or stock carts with a lot of additional on-cart hardware (such as a HOKEY or a POKEY). My current theory is that the power supply is not fit for purpose. I've ordered a 9VDC / 2500 mA Triad Magnetics power supply to try out as my next cheapest option as I debug. Thank you, all, for the suggestions. Tune in next week for the next installment to this drama. 🙂

You may not hear it on the video but the ping-like sounds are produced as the text is printed.

I broke out my 1Up card and some IPA to clean the game contacts (that looked pretty darned clean to begin with) and no change in behavior. I ordered some Dioxit from the almighty Amazon I can try spraying in the cart slot when the order arrives this weekend. At least the failure mode is consistent.

...but, given that I live in the Hill Country, it might be for me if you're willing to meet up for some debugging.

This past weekend at VCFMW, I picked up a copy of Attack of the PETSCII Robots from David Murray, The 8-Bit Guy. I fired it up today, ran in to problems, contacted David and he's pointed me to y'all. I get the initial color Atari logo and get to the next screen of detecting human presence, but when it segues to the title screen and kick off the POKEY music, it crashes. Usually it plays some tone with a solid color screen, then sometimes after a few second changes to another color screen and another tone. Sometimes I just get a black screen and no tone. I don’t have this problem with any of the other several dozen 7800 carts and countless 2600 carts I have, though this is my first ever cart with a POKEY soundtrack. My 7800 is lightly modded (nothing too exotic): UAV for composite video mod, blue power LED, and a standard barrel connector for the power adapter. I guess it’s possible the UAV is causing me trouble, but I suspect the Venn diagram of UAV modded 7800’s and PETSCII Robots has some decent overlap. I *did* read the friendly manual and the insert, but found no hints. Obviously tried reseating the cart a few times, but no love. Any thoughts for next steps? Thanks for your help! Dan in Austin