Conversation

Notices

1. Embed this notice
   Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:47:55 JST Dan Fixes Coin-Ops

   in reply to

   In the real world, what's actually happened is you've turned the game on, and for the first blink of an eye, all is chaos.

   The power supply's still waking up, current is rushing into capacitors to charge them up, you might be giving the processor a volt, two volts, half a volt, you don't know, and the memory chips it's connected to might be getting different voltages too - your five-volt line is still getting charged up and nothing's ready yet but that processor, man, it's AWAKE and it's ALL FIRED UP

   (big smoothing capacitors are in this system, to ensure that your 5v line is a nice smooth steady 5v, not ripply or going higher when the computer's not working hard and lower when it is or anything like that)

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:47:56 JST Dan Fixes Coin-Ops

     in reply to

     Right where to start

     Okay, you've seen a computer chip right, big black thing with dozens of little silver legs coming off it, well each of those legs has a job to do. Your most basic job of any chip is, put electricity out of a combination of one or more legs, based on the combination of electricity going into one or more legs. That's true whether we're talking about the Motorola 6800 that Baby Pacman uses, or the whizbang processor in your phone.

     In most chips the question of "Is there electricity going into this leg" is a rather coarse one, in that there's no "Well yeah a bit," it's either "Yes there is" or "No there isn't," and back in the day, chips ran on five volts. New ones run on 3.3 or even lower, but back then it was 5v (some used 12v too, for example some memory chips used 5v to read and 12v to write, but we're concerned with 5v now).

     So the question we've gotta ask ourselves is, does four and a half volts equal a "Yes there is" or a "No there isn't"

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:47:56 JST Dan Fixes Coin-Ops

     in reply to

     In an ideal world, you turn a game on, electricity goes into the processor, it wakes up and goes RIGHT THEN MEMORY CHIPS, WHAT'S MY FIRST JOB, WHAT'S AT MEMORY ADDRESS ZERO, and it looks at the sixteen wires connected to its "Address" legs and some attached ROM or RAM chip will stick its hand up and go "ME FIRST BOSS" and off it goes doing its job.

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:47:57 JST Dan Fixes Coin-Ops

     in reply to

     Alright Dan so this is supposed to be an easily-accessible account for the technically-curious-but-not-necessarily-technically-proficient, what the hell's a reset section

     Alright so the reset section's job is to say to the computer, "WAIT - just, just bloody WAIT a SEC you little - alright go!"

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:47:58 JST Dan Fixes Coin-Ops

     in reply to

     Noticed that some of my scores didn't end in 00, too.

     I mean, that's a pretty good error-check there - pinball scores always end with at least one 0, and you might well assume that in the computer they're stored divided by 10 and then there's a dummy display digit that's always 0, and that was true on electromechanical games but on solid-state games the computers actually store the whole score in memory, meaning that a score that doesn't end in a zero is a REAL NICE CLEAR OBVIOUS INDICATOR that you've got PROBLEMS, maybe a RAM chip's going bad or this thing got hit by a particularly angry Cosmic Ray or something, either way take the dollar bills off the glass 'cause these scores ain't valid uh I mean no gambling amusement only

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:47:58 JST Dan Fixes Coin-Ops

     in reply to

     So I play some games and clear some scores and set some new ones and figure out what's what and the headline is this:

     This game doesn't always boot, and when it fails, battery-backed-up data gets messed up.

     So, what that battery acid was eating was the computer's RESET section.

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:47:59 JST Dan Fixes Coin-Ops

     in reply to

     Alright so, what was happening with this game.

     Well, my Pinball Initials are CMJ, that's short for CavemanJoe, which is the name under which I run Improbable Island, so this thing was packed full of scores that were all CMJ.

     Now. One day I go to turn it on, and it doesn't turn on. Normally it plays a weird slowed-down slightly spooky version of the first half of the pacman song as the sound computer slowly comes to life, while the videogame and pinball computers take like five seconds to do some self-tests, and then it goes into attract mode. Well I got the sick sounding half-a-song, but no coil click and no lights and nothing on the screen, so I go "Oh haha here we go" and I turn it off and on again and this time it comes back and works alright.

     And it gets to the high score screen and I go "Hang on a sec. Who the hell is BMJ?"

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:48:00 JST Dan Fixes Coin-Ops

     in reply to

     Anyway I'm putting off explaining to y'all why this thing was broken, because it's very tempting to say "The battery leaked and ate some stuff."

     (see back when persistent storage cost £oadsamoney, you'd just hook up a battery to your RAM chip if you wanted to save high scores and stuff. Williams used 3 AA's, Bally and Gottlieb used a board-mount rechargeable NiCd. Thousands of pinball computers have been destroyed by leaking batteries)

     Anyway yeah I could tell you that and that'd be very neat and tidy but the details of WHAT the battery ate are WAY jucier and more interesting. My problem is I try to keep this a super accessible account so explaining what the eaten bits did and why that meant the machine ended up doing what it was doing would involve explaining how a computer works and that scares me a bit 😅

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:48:01 JST Dan Fixes Coin-Ops

     in reply to

     I mean, it makes sense that the score lives in the pinball computer, I suppose, I guess, they've already made the pinball computer to keep score and it's been doing it for a few years and they know it works, but still

     Baby Pacman: "Mom can I have a scorekeeping subroutine"
     Bally: "No honey, we have scorekeeping at home"

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:48:01 JST Dan Fixes Coin-Ops

     in reply to

     Other pinball machines in the early 80's only stored the highest score, no initials, that didn't happen until alphanumeric displays came about in like, ooh, I dunno, I wanna say like '86 ish - Baby Pacman stores the top eight WITH INITIALS

     On the SAME COMPUTER with the SAME 5101 RAM CHIP

     And yeah, we know the initials and the other high scores live on the pinball computer, because that's the board the battery lives on and you can defederate it from the videogame computer and it still remembers

     Now is that, maybe, why this game is only 2 players instead of 4 like every other early 80's pin? It had to sacrifice two players' game states' worth of memory space to keep track of initials and extra scores?

     Also that'd free up 2 players' worth of display wires to communicate with the videogame computer

     It's a miracle this thing works at all

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:48:02 JST Dan Fixes Coin-Ops

     in reply to

     So the pinball computer is a bog-standard Bally pinball computer (or MPU as they're called in pinballland) from the early 80's. There's one diode of difference between Baby Pacman's MPU and other regular Bally pinball MPU's. So how the hecc do it work

     Well remember the orange numerical score displays on 80's pinball? Yeah it talks to the videogame board through the wires that would've gone to those displays

     And the videogame computer talks back to the pinball computer through its playfield switch inputs

     and your score lives on the pinball MPU

     So when you're playing pacman, the computer that keeps track of your score has NO IDEA WHAT'S GOING ON, it just gets told by the videogame computer "Increase the score" and it doesn't know why

     this is the board that the high scores are saved in also

     but your score is shown on the video screen

     which is plugged into the videogame board

     so...

     ...what's going on, does the videogame computer keep its own copy of the score which it spits out on the screen? No it can't be that, because then WHAT HAPPEN IF THE COMPUTERS DISAGREE, so I guess the videogame computer goes "Increase the score by 100 points, I am simulating pressing this playfield switch that scores 100 points," and then sixty times a second asks "Remind me what's the score again so I can show it to the player," is that really what happens? How bad do I wanna find out?

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:48:03 JST Dan Fixes Coin-Ops

     in reply to

     (I know I only tend to update this thread when there's really ridiculous fedi meta, I didn't even check today whether there WAS any current meta, which is a shame because)

     See the way this game is supposed to work is that it's organized by three computers who resent each other

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:48:03 JST Dan Fixes Coin-Ops

     in reply to

     You see three boards in that photo and you might think one board per computer, nah, the one on the left is the power supply/driver board, the bottom board has the videogame computer and the sound computer, the top board is the pinball computer

     Guess where your score lives

   • Embed this notice
     Dan Fixes Coin-Ops (ifixcoinops@retro.social)'s status on Sunday, 03-Dec-2023 01:48:04 JST Dan Fixes Coin-Ops

     Baby Pacman thread update, when you say things like "Aye the vinegar smell is 'cause I was giving the computer a bath, I'm all done sanding it now," you know things have taken a turn eh

     Cor but just look at that bare-copper-and-green, that's some Aesthetic there innit