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Missile Command / Asteroids deluxe repair log

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Monstermug View Drop Down
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    Posted: 04 Nov 2017 at 7:50pm
Not much time to fix anything of any interest recently or at least take the time to documentate it anyway.  

Got two boards on the bench today.  An asteroids deluxe and Missile Command.  Asteroids was reported to have a rapid clicking coin mech on start up.  Straight away I new the watchdog was barking and probing reset pin on CPU proved this.  With probe on reset Pin 40 of 6502 I pressed around the board until I found that the the culprit.  CPU socket was bad.  Replaced this and the game works.  

Missile command was next.  Reported to have blue screen on startup.  Hooked up a quick and dirty jamma adapter for power and video.  Got a blue screen.


Found a missing .1uf 25v radial cap at C42 so replaced that with a 104. 

Probe reset pin and that seems to be acting normal and so was all the address lines.  Game seems to be running.

Decided to hook up the famous "philmur audio probe" as my adapter didn't include sound.  Grounded test point to ground and heard the low beeeeep high bip sounds which I think means that self test passes.


As someone has previously shotgunned this board before and socketed all ram chips, I decided to try replace all 4114s with known working ones.  It didn't do any difference.  

Next I turned my attention to the graphics section, specifically the colour pallet.  Probing L7 showed w/e line of pin 3 held high.  This signal comes from 7442 decoder at E8.  Probed E8 showed all outputs stuck high although the 4 inputs were toggling as normal.  Removed this chip and replaced with 74LS42.  


And was greeted with this: 



Game seems to be fully working but no trackball to test it and no time to bodge one up. 




Edited by Monstermug - 04 Nov 2017 at 8:39pm
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bonehead View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bonehead Quote  Post ReplyReply Direct Link To This Post Posted: 04 Nov 2017 at 9:10pm
You are a genius!!!!

2 of the best arcade games live again. Time to dig out my salamander pcb to see if you can work your magic for me.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurray Banana Quote  Post ReplyReply Direct Link To This Post Posted: 04 Nov 2017 at 10:02pm
Cracking bit of fixing
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Post Options Post Options   Thanks (0) Thanks(0)   Quote neil1637 Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 2017 at 8:39am
Great fixes.
Please visit my Arcade Diary Blog at https://neilsarcadediary.wordpress.com/

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark H Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 2017 at 5:28pm
Excellent - we must save Atari games !!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philmurr Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 2017 at 5:43pm
Nice fixes, Missile Command isn't the easiest of boards to work on Thumbs Up

Good to see the old audio probe being used in anger!

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