Game Platforms-

  • and sell inexpensive Jamma PCB that plays defender well, based on mame emulation.
  • occasionally offers a multi-williams board that plays Defender with real hardware, no emulation. 100% accurate gameplay experience.
  • MAME does a nice job of emulating Defender from your PC
    • Interfacing your laptop with arcade controls is best done with an Ultimarc I-Pac
  • Technical Info for swapping out games or rom sets on a JROK board HERE

Graphic Fonts-

PCB Repair-

  • Board repair- Contact Ken Graham/Yellowdog on KLOV forums
  • Defender Boards to service/sales-
  • Power Supply rebuilds- Contact Dave Okert/DOKERT on KLOV forums

Defender Settings

The following info is taken straight from the Williams booklet on Defender.


1.  In game over mode, set switch to AUTO-UP and depress ADVANCE. The CRT indicates Function 1 and total left chute coins.

2.  Record audit totals and depress ADVANCE for functions 1-7. To review a total that has been advanced past, set switch to MANUAL-DOWN and depress ADVANCE.

Functions are displayed one at a time as follows:-

  • Function    Total    Description
  • 1                   0          (Total) COINS LEFT
  • 2                   0          (Total) COINS CENTER
  • 3                   0          (Total) COINS RIGHT
  • 4                   0          TOTAL PAID (Games)
  • 5                   0          (Total Bonus) SHIPS WON
  • 6                   0          TOTAL (Play) TIME (Minutes)
  • 7                   0          TOTAL SHIPS (Played)

3.  Operate ADVANCE to display Function 28, SPECIAL FUNCTION. From Function 28 you can return to game over or zero audit totals and return to gameover.

4.  With switch set to AUTO-UP, perform a. or b. as desired.

  • a- To return to game over depress ADVANCE.
  • b- To zero audit totals and return to game over, operate HIGH SCORE RESET to indicate “35″ on CRT Function 28 and then depress ADVANCE.

——-GAME ADJUSTMENTS (Functions 8-27) ——–

1. In game over mode set switch to AUTO_UP and then depress ADVANCE. The CRT indicates Function 1 and total left chute coins.

2. To raise Function number on CRT, operate ADVANCE pushbutton with switch set to AUTO-UP. To lower Function number operate ADVANCE with it set to MANUAL-DOWN.

3. With desired Function indicated, raise adjustment value by operating HIGHSCORE RESET with switch set to AUTO-UP; lower value by operating HIGHSCORE RESET with it set to MANUAL-DOWN. Value left on CRT is new setting.

For values, see below and, for pricing

Function   Factory Setting   Description (note that the bold defaults are RED ROM)

  • 08           10000        BONUS SHIP LEVEL (0=No Bonus Ships)
  • 09               3        SHIPS PER GAME
  • 10               3        COINAGE SELECT
  • 11               1        LEFT COIN MULT
  • 12               4        CENTER COIN MULT
  • 13               1        RIGHT COIN MULT
  • 14               1        COINS FOR CREDIT
  • 15               0        COINS FOR BONUS
  • 16               0        MINIMUM COINS
  • 17               0        FREE PLAY (Set to 1 for Free Play)
  • 18               5        STARTING DIFFICULTY (0=LIB; 1=MOD; 2=CONS)
  • 19              15        PROGRESSIVE WAVE DIFFICULTY LIMIT (4-25) e.g. 5-LIB; 10=MOD; 15=CONS;
  • 20               1        BACKGROUND SOUND (0=OFF; 1=ON)
  • 21               5        PLANET RESTORE WAVE NUMBER
  • 22               0        NOT USED
  • 23               0        NOT USED
  • 24               0        NOT USED
  • 25               0        NOT USED
  • 26               0        NOT USED
  • 27               0        NOT USED

4. Repeat steps 2 and 3 until all desired adjustments have been made.

5. Operate ADVANCE until 28 0 SPECIAL FUNCTION is indicated on CRT. From Function 28 you can return to game over or restore factory settings.  Perform step 6 or 7 as desired.

6. To return to game over, depress ADVANCE with switch set to AUTO-UP.

7. To restore factory settings and zero audit totals:

  • a- Operate HIGH SCRORE RESET in AUTO-UP to indicate “45″ on CRT Function 28.
  • b- Depress ADVANCE. The game returns to audit Function 1.
  • c- Set switch to MANUAL-DOWN and depress ADVANCE to indicate Function 28 on the CRT. d- Set switch to AUTO-UP and depress ADVANCE.


  • To reset the high score to the factory settings and erase signatures, depress HIGH SCORE RESET in game over mode.

Difficulty Label History (Larry DeMar Jan 2013)

  •  Hard for the player is a conservative setting by the operator.
  • Easy for the player is a liberal setting by the operator.
  • The manual and operator settings were created for the game operator’s point of view, with setting history going back to electromechanical pinball machines with jumper wires that changes the settings.  Often there were tags next to jumper blocks showing “Cons” or “Lib” to help guide these selections.

Goldilocks zone- (Larry, May 2013)

  • As to the 990,000 behavior, it took months for the highest scores we saw to creep from 200,000 to 300,000 on upward.  I was with Eugene, at a location where John McCue, our local Chicago Ace (who went by ACE on the High Score Table) put up a score over 500,000.
  • He (Jarvis) said at that time that he thought something interesting may happen when the player gets to 1,000,000 (rolling the score).  He went back to the code the next day and verified that you would get “an advance” of 1 ship from future ships earned for each scoring event between 990,000 and 1,000,000.  Thus if you hit more lower scoring objects during this window you will rack up more ships.
  • He made the conscious decision to leave this new “feature” out there and history indeed confirms that this was a brilliant move.
  • I mention John McCue as our Chicago Ace as Doug Mahugh still lived in Seattle at the time and was working along the same curve in parallel.
  • Paul Spriggs’  Youtube demonstration

ROM Variations and Difficulty- (per MOS)

UPDATE July 2014- Help Andrew Welburn with his history of Williams boards HERE

There are 3 official ROM sets for Defender: Blue, Green and Red (released in that order) and a nebulous White set rumored to be prior to blue. They all differ to some extent, and all have separate Instruction Booklets (the smaller format).

  • A collector told me he estimated Red ROM machines outnumbered the Blues/Greens by a 7:1 ratio. And that the Green ROMs strongly outnumbered the Blues. An estimated total of 55-60.000 units were produced.
  • Blue ROM set – Runs the game on 10 ROMs (#4 and #5 not used). – Early series CPU – The ROM board has different jumpers than the Green and Red ROM boards. – The attract mode reads: “LANDER 100”
  • —-Instruction Booklet #16P-3000-103 (no date) reads: Function #18 = Starting Difficulty: 0=LIB; 1=MOD; 2=CONS (Factory default=0) Function #19 = Progressive Wave Difficulty Limit, 4-25, e.g. 5=LIB; 10=MOD; 15=CONS (Factory default=10) Function #20 = Background Sound: 0 = OFF; 1 = ON
  • Green ROM set – Runs the game on 11 ROMs (#5 not used) – Early series CPU – The attract mode reads: “LANDER 100”
  • —-Instruction Booklet #16P-3001-103B (March, 1981) reads: Function #18 = Starting Difficulty: 0=MOD; 5=CONS (Note: no LIB setting) (Factory default=0) Function #19 = Progressive Wave Difficulty Limit, 1-30, e.g. 01=LIB; 10=MOD; 20=CONS (Factory default=10) Function #20 = Not Used
  • Red ROM set – Runs the game on 11 ROMs (#5 not used) – Later series CPU (which made it possible to flip the screen for the cocktail version) – The attract mode reads: “LANDER 150”
  • —-Instruction Booklet #16P-3001-103 R-T (July, 1981) reads: Function #18 = Starting Difficulty: 0=LIB; 5=MOD; 10=CONS (Factory default=5) Function #19 = Progressive Wave Difficulty Limit, 5-30, e.g. 5=LIB; 15=MOD; 25=CONS (Factory default=15) Function #20 = Not Used
  • Note: difficulty never progresses beyond 30 (for function #19): a game set to 05-30, will play exactly like a game set to 05-00 (=100). Difficulty 30 is max.
  • For hardware differences between the CPUs/ROM boards, see here:
  • Williams Video Games Hardware Identification and Compatibility:….html#defender

White Rom Set-

  • Info regarding Andy Welburn’s dump of white roms.  ( defenderw )
  • This is probably the very first production romset before Blue roms
  • This file is the original white roms with modification to rom 10 because checksums didn’t match after it was dumped.
    The other defendw file is simply early blue roms masked as white due to an honest mistake because the blue mark faded.
  • Shows a Defender with the scoreboard many of the bootlegs have – i.e. DRJ 20000, SCD 18000, etc.
  • Mame v141 can run this file, Mame v106 can not.
  • Larry DeMar July 2014- I can’t be certain on this but it looks to me like this is an early version of the game. SCD (not SCF) would be Sam Dicker who probably made the choice to change to SAM. KJF is indeed Ken Fedesna. Eugene probably made the call to add Steve Ritchie to that spot in the table and made the tough choice to remove Ken for that purpose. I don’t remember this specifically happening, but the white label roms in that board strike up a visual memory for me and this speculation would be consistent with what I see in that picture and the two HSTD tables. In the video, the self-test is showing “Unit OK” so it isn’t a ROM error, at least not to the extent of each chip reading out its contents to match a checksum. There may have been a hardware change where the “older” white roms don’t correctly operate the newer hardware in your game. That’s the first thing that fits these facts for me but I just don’t remember.
  • Historical perspective per Ed Thomas- Artik International was sued by Williams Electronics for copying and selling the roms (very early in release)  to a number of companies with similar interests. Many  “kits” were sold, word got back to Williams rather quickly about what was happening and Williams immediately filed a lawsuit. See:  This is how so many early bootleg versions were released back in 1981. It’s not too uncommon to find (their) code mimicked to the ones produced by Williams.
    Gameplay, size, sounds, the lay of the land, etc. are all similar, hence the reasoning for lawsuits. Williams won of course, but the code was leaked. Which is one of the reasons it makes this topic of the “Original White Rom Set” rare and important.


ROM Versions- (Larry DeMar May 2013)

  • May 2013- My memory is foggy on the timeline for the updates but I seem to remember that they were done early on.
  • Oct 2013- I would consider updates (refinements from Green to Red) to be Eugene’s intended work, refined from experience. Once Red was released, Green was merely another stage of Prototype.

Gameplay differences between the ROM sets. The ROM sets are not equally hard to play.

  • On any given setting, the Blue ROM set is harder (=faster), than the other two ROM sets. This is mostly felt on easy/default settings (B/G=00-10; Red=05-15), but goes all the way up to max (99-99), though here the difference between the Greens and Blues is hardly noticeable anymore.
  • On the Blue and Green ROMs difficulty can be set to escalate all the way up to max/99 (or actually 00, to be exact), whereas on the Red ROMs difficulty stops at 30 (function #19): 30 is max (even though you can set it to 99-99, it will play exactly like a 99-30 setting).
  • This difference in difficulty between the Blue/Green ROMs and the Reds is not as huge as the figures seem to imply: between difficulty 20-30 the Baiters are becoming a real problem, and effectively stop most players from marathoning Defender – on any ROM set.
  • The Baiters are not getting much harder after 30-35 (on any ROM set), and are not the biggest difference between the Blue/Green ROMs and the Reds – the Landers are. Around difficulty 65 they’re lifting humanoids so fast the game can’t handle their logic very well any more: they very often take an extra lap (or two) through the ceiling, and out through the floor again. Landers also often get stuck when trying to lift humanoids, spraying bullets like crazy.
  • And ‘Space’ is monstrous: the ‘Dateline’ seems to be following you everywhere, so often when you turn on the Mutants, they’re going the other way – fast. The usual strategies don’t work anymore. Hyperspace mostly feels like a suicide-button – it’s really the last way out.

The difficulty settings for playing 5-man Defender, i.e. the Twin Galaxies Tournament Settings (aka ‘TGTS’), are the default settings for the Red ROMs: 5-15. There’s no mentioning of what ROM set to play, but the Reds are implied by the 5-15 default setting (because default on the Blue and Green ROMs is 00-10). But the Blue/Green ROMs set to 5-15 are noticeably harder than the Red ROMs on 5-15 (and the Blues clearly being harder than the Greens). So if you’re trying to improve on your TGTS score: be sure to play the Red ROMs.

Max difficulty is 99-00

  • Gary and I have deduced, since 00 is max (=100) for Prog Wave Diff (#19).
  • But bitd we all had it 99 was max, so ’99-99′ is what we still say.
  • There SHOULD be a difference, but so microscopic there is no way to tell the difference. But just for the sake of it, I set it to 99-00 nowadays.
  • Try setting the game to 00-00, and you can clearly see that Starting Difficulty seems to apply to waves 1-4.
  • There’s a brutal jump in difficulty between waves 4 and 5 – and especially so on the blue & green roms.

How the difficulty settings work.

  • This is a good way of thinking about them:
  • Starting Difficulty means what difficulty wave 5 will be – waves 1-4 are merely adjusted to make an even progression of difficulty up to it.
  • Progressive Wave Difficulty Limit is the maximum difficulty the game will reach – at SOME point.
  • A 5-15 setting means wave 4 will be at difficulty 5, and that wave 15 will be at difficulty 15. Think: “15 minus 4 = 11. Difficulty will escalate for 11 waves, starting from wave 4.
  • ” 99-99: “99 minus 99 = 0. Difficulty will escalate for 0 (zero) waves, starting from wave 4.
  • ” 30-10: “10 minus 30 = -20.” But you can never have a game with decreasing difficulty, so all negatives are treated as ‘0’.  This is the same as a 10-10 setting.
  • 00-99: “99 minus 0 = 99.” Difficulty will escalate from the absolutely easiest possible setting, to the absolutely hardest (almost), during the course of 100 waves, counting from wave 4. Difficulty 99 should be reached at wave 104 (?).

More Example from MOS- (Feb 2013)

So the Red default settings – 5-15 – spelled out looks like this:
Wave 4 = diff 5
W5       = diff 6
W6       = diff 7
W7       = diff 8
W8       = diff 9
W9       = diff 10
W10     = diff 11
W11     = diff 12
W12     = diff 13
W13     = diff 14
W14     = diff 15

  • And on the Green ROMs it’s 100 steps/waves of difficulty progression on the 00-99 and 01-00 settings. On the Reds nothing happens after wave 30-35 on those settings, whereas the difficulty on the Greens just keeps going for 100 waves (wave 4 to wave 103), when diff 99 or 00 (100) is reached. But the biggest increase in difficulty – by far – occurs waves 1 through 30-35 on those settings (on both sets).
  • There are only 2 settings where the difficulty increases for 100 waves (not counting waves 1-3): 00-99 & 01-00. And only on the green (& blue) ROMs.
  • #18 – Starting Difficulty: 00  Here ’00’ means ‘zero’ – the easiest possible setting. ’99’ = the hardest.
  • #19 – Prog. Wave Diff. Limit: 00  Here ’00’ means ‘100’ – the hardest possible setting.
  • This is all clear when you set the game to 00-00 – i.e. the brutal jump in difficulty between wave 4 and 5.
  • So the hardest possible setting is actually 99-00.
  • And the easiest possible setting is 00-01.

Planet Restore value explained, random conversation:

  •  Question from Paul Spriggs- How many of you have noticed that the game adjust mode that allows you to change this(setting 21) is in 16 bit hex? This means you cant, for example set the game to refresh every ten waves, as if you set the value to 10 it restores the planet every 16 waves, as 10 in hex = 16
  • It means you are limited to the planet restore options. You can set it to 9 and they will be refreshed after each 9 waves. Set it to 10 and its every 16 waves. Set it to 11 and it will restore every 17. Set it to 20 and its humans back every 32. I wonder if Larry or Eugene can explain why ONLY this particular value is in hex, not decimal, and also can we ask Larry DeMar and Eugene if they are sick to death already of answering a string of silly questions!
  • Guess from Jim Bowley- The user settings menu uses binary coded decimal to make it easy to interact with the user, but when the programmer coded the Planet Refresh he forgot it was BCD. And probably no-one tested it above 5.
  • Larry DeMar confirming Jim’s suspicion- The setting menu was programmed by Paul Dussault and the number is stored in BCD.  The number was then used by the program without converting it to binary.  I assume that Eugene tested the “factory setting” of 5, and maybe even another value, probably 1 or 2 without noticing that he didn’t convert the BCD number to binary.  –Oct 2013 via the WDPU group

Defender Artwork-

Generic Control Panel Overlay (CPO)

Original CPO-


Cabinet Artwork-

  • Prototype Defender plus a licensed Italian version cabinet by Video GElectronic GamesLINK
  • Regarding Color decal instead of stenciled red/black- There were lots of games with that decal (rather than the yellow and red stenciled paint that adorned most of the the cabinets).  Certainly hundreds.  Maybe thousands. – Larry DeMar, Nov 2012
  • The original artwork was stickers for prototype games. These were cost reduced to stencils. – Eugene Jarvis, Apr 2014
  • Talked to Connie (Constantino) Mitchell the artist, and he confirms its the real McCoy. The first 4 or 5 protos had full color art stickers as opposed to the cheap-ass stencil that was produced. I remember being somewhat indignant about the switch at the time. – Eugene Jarvis, 2004
  • Yes, this shows the Defender man is based on KLAW from the Fantastic Four comic book series! Issue #56, Nov. 1, 1966


Stencil Information-

The cabinet front typically had red stars, but repainted cabinets tend to have yellow stars.

  • GameStencils sells the closest reproduction product, but the die-cut material is a very light membrane, very difficult to work with, and the end result doesn’t have the nice edge fade of original stencil overlay sheets, due to the sticker adhesive.

As seen in these images, the actual stencils used for cabinet artwork varied.


Sometimes the right side of the cabinet has the astronaut facing front, the more correct but more rare version has him facing backwards


  • We (Williams) would have applied the decal sides (colorful stickers noted in prototype above) at our factory, but any painted stencil work would have been done at our wood cabinet supplier. When we first started building Defender, we were in a small factory space on Belden Avenue where Williams had previously designed and built slot machines. We never expected Defender to be as big of a hit as it turned out to be, so not a lot of factory space was ever contemplated being needed. There never would have been room in the Belden facility to be spray painting on the side cabinet art. Because of the success of Defender, Williams started looking for more manufacturing space, which turned out to be a factory facility up in the Gurnee, Illinois area. – Ken Fedesna, Apr 2014
  • We (Williams) never painted anything (other then touchup) internally at either the Belden facility or the Gurnee facility. All cabinet art, both the base coat as well as any stenciled art that was painted on the cabinet, would have been done by the external cabinet suppliers that we used back then. – Ken Fedesna, Apr 2014

Don Hodges Explains The Reverse Button

  • some players report the reverse button will intermittently stop working during busy play
  • My initial analysis of the reverse button gives the following information.  When the reverse button is pressed, a subroutine to handle it is called.
  • First the sub checks to see if a reverse is already in progress, if it is, then the sub aborts.  Else, a flag is set to indicate the reverse is in progress and the reverse is implemented.
  • Then, a small delay is programmed and regular game play commences.
  • After the delay, which i think is 2 interrupt cycles, the sub returns and then checks to see if the reverse button is still being pressed.
  •  If it is, then the code loops back to the small delay again and this is repeated until the reverse is not pressed.  After this, another small delay of 5 interrupt cycles is programmed and game play commences.
  • After this delay, the flag is cleared, which indicates that the reverse is complete, and then the subroutine is finished. So, if you hold down the reverse button, you only get one reverse.  Also, if you press the reverse button twice in a row very rapidly, you get one reverse instead of two.
  • The reverse button is handled in hardware by the same circuit that controls the fire button, thrust, start buttons, smart bomb, hyperspace, and joystick down, so they *should* be all given equal priority, but perhaps you cannot press several at once and expect them all to work.

6809 Assembly Language and Code


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