Replacement chips for original arcade hardware - what is allowed?

  1. Replacement chips for original arcade hardware - what is allowed?

    11-14-2019, 08:59 AM
    Hi there, I am new to this site, and have some questions on what is allowed in terms of replacement chips for original arcade hardware to still qualify a board as valid for achieving world records.

    I repair arcade circuit boards, and many of the original chips are becoming very expensive or obsolete, difficult to program without expensive and ancient 30 year old programming machines, or are no longer manufactured and impossible to find. There are modern alternatives and equivalents now, and replacement implementations that don't materially alter gameplay.

    In particular, I would appreciate some clarification on the following items as to whether or not they would disqualify a submitted score:

    1. Replacement of one kind of RAM with another. For example on a Williams board, replacing older, hotter 4116 with 4164, and modifying board to remove the 12v and -5v voltages that original RAM required.
    2. Replacing static ram with nvram or battery backup ram for saving high scores. For example replace 6116 and onboard battery with 6116 nvram chip, such as this one:
    3. Replacing a hard to find and program PAL chip with an easier to find GAL, for example PAL2GAL conversions found here:
    4. Replacing an obsolete custom chip with an alternative reproduction, such as these: ( or Caius' amazing chip work (
    5. Replacing one original TTL with another variant, for example 74LS161 with a 74S161
    6. Replacing bipolar proms with alternative implementations like this:
    7. Combining multiple original hard-to-find ROM chips into a single ROM with larger capacity, for example:
    8. High score save/freeplay kits that modify the program roms only slightly to add Free Play capability and/or HSS
    9. Use of higher quality chips instead of original spec chips (like using a 6116 instead of a 2016 ram chip, use a z80b instead of z80a, etc.)
    10. Replacement of crystal oscillators of a certain speed that can't be sourced anymore, with the next closest value crystal
    <- Any other items that others can think of? ->

    To illustrate the challenge for a board repairer these days, lets say that a broken board has a dead PAL chip. I could choose to replace this with a modern GAL equivalent, at $1 per chip, using an inexpensive USB programmer for $40-$50, or I can replace with an original chip at $10 per chip, and requiring an antiquated 30 year old programmer that only runs on Windows XP and costs $500 used off of ebay. For functionally the same output, the choice in terms of cost to repair is a big one, but I don't want to do that and render a board unsuitable for achieving a world record on.

    On games that originally had batteries and did save high scores and/or game stats (such as Pole Position), these batteries are 30 years old, leaking onto the boards and ruining them. I would love to be able to remove these batteries and replace with a RAM chip that just persists the same data that the original RAM chip did, just without the corrosive battery in place. Some games were never built with the ability to save high scores between power ups, and those usually require some sort of ROM code modification to prevent the high score table being reset on power-up with dummy entries, so I could understand not allowing that change for those kinds of games, but it would be great to have a little more clarification specifically around what is allowed other than just it needs to be on "original hardware".

  2. 11-14-2019, 10:06 PM
    Thanks for posting this, Adamt - a great question! Where does "unmodified original hardware" cross the line into something where the "original" is lost with necessary repairs and part replacements?

    I'm not sure the community will be able to articulate a clear consensus on this question given the broad range of situations that can occur with a PCB repair - it may just require a declaration from TG leadership. My own personal view is that repairs to original hardware - including substitution for parts like RAM or CPU - should be permissible based on the premise that such changes would not bestow an "unfair advantage" to someone playing on that hardware. There has to be a degree of trust that repairs such as the ones you've outlined are conducted to keep classic games up and running. At the same time, those repairs could be scrutinized if it appears that they materially impacted the game operation when evaluating video evidence of the submissions. What do others think?
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  3. 11-17-2019, 08:18 PM
    Agreeing with The Evener. Nothing described in the op stands out as being something other than preservation. We can point to hi score kits on donkey kong being permissible, various cps2 preservation efforts (darksoft kit, suicide battery deletion solutions) being permissible. I think everything proposed in the op is generally in line with these degrees of precedent that have already been set.
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  4. 11-18-2019, 04:15 PM
    There is nothing wrong with any of the above mentioned replacement parts. The games are based on timing and cpu control signals. So replacing a chip with a faster, or slower, or better, or made from other sources don't affect the outcome of the game. Only the processor and or program roms can affect game play to the advantage of the player. Well 99% true, there are probably some instances where it might benefit the player. Most repairs have little to no affect of the gameplay, there is only a small percentage of the board that controls the game play and the rest is devoted to other task that wouldn't have a postive affect for the player.
  5. 11-19-2019, 02:19 PM
    So what about a cause like with Atari Gauntlet, where to get around a missing Slapstic protection chip, the slot has jumpers installed and the machine has a patched ROM that allows play in this manner? Yes, it is a change to the game's code, simply to get around this difficult-to-replace security chip.
  6. 11-21-2019, 12:21 PM
    Quote Originally Posted by GibGirl View Post
    So what about a cause like with Atari Gauntlet, where to get around a missing Slapstic protection chip, the slot has jumpers installed and the machine has a patched ROM that allows play in this manner? Yes, it is a change to the game's code, simply to get around this difficult-to-replace security chip.
    I think this is similar to what YesAffinity mentioned regarding getting around suicide batteries too, which often require an unencrypted rom/s different from original, or just plain unencrypted roms on games that had encryption modules or encrypted CPUs encased in epoxy (Sega games like Turbo, Future Spy come to mind).
  7. 11-23-2019, 09:55 PM
    I'm also interested in these guidelines. This should be clear and maybe score submission should add that extra step to show the board better, not that just it's there. Control panel view from the bottom as well. Basic things, such as a switching power supply used as a replacement should also be mentioned by TG. Replacement of original joystick/spinner, etc. with a better one should be mentioned. Basically, all the possible solutions as yes or no for today's gameplay. Something like a "guidelines to submit and validate your high score."

    10. Replacement of crystal oscillators of a certain speed that can't be sourced anymore, with the next closest value crystal
    I would say this one would certainly be a no no, if you wanted to use it to set some official score. For home use it's fine. The crystal will alter cpu clock and, depending on frequency, make the game either faster or slower. If you want to marathon a game, such as Nibbler, you would benefit from a bit faster game (assuming you are good at the patterns for it). Imagine shaving a few hours off your time to get the high score. That exact problem happened to Dwayne Richards at an event for Nibbler, if I recall correctly. His game was running faster and in the end his score didn't count. Other games, such as Donkey Kong, could benefit from a slower frequency crystal, to make the game bit slower/easier. Of course I'm talking about +/- 1-3% in crystal frequency max.

    If you repair boards, I think it's important to attach a note with changes made to the board itself. If the board is repaired, but all original, that's important as well and should be written and attached to the board. Imagine, if someone went for a high score and later found out that his board was not "legit" due to a recent repair that altered the gameplay. Safely attached note to the board will be much better than an email to the customer (who has no idea what that means) stating the changes. When it's resold, that note would travel with the board and a new player would not risk getting his/her score negated due to changes done by previous owner.

    Think using unencrypted roms and chips with patched code should be done as per game basis. This also should be cleared by TG. As time goes by, more and more rare chips will fail. Running the board to the original specs might be a real challenge. All that before you even start playing the game and try to go for the high score.
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