Couple of Missile Command Repairs

lilypad19

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Donor 7 years: 2019-2025
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*** Note: I format these in a browser - not sure how they will come up on a phone. They are cross posted from my site :) ***

This is one of mine..

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This is the 'after' shot. Arcade customer sent in a MC board for repair (next one below) but wanted a spare since Missile Command is now down at their arcade. I had one that I'd picked up a while back and got it running while it is in transit. This particular board had a lot of little things wrong with it.. One thing I do like is the RAM are all ceramic packages. It had no RAM or ROM errors. It's not the brightest and shiniest board I've ever seen. I did wash it.

Items of note:
  • Missing Power LED - replaced
  • Missing Q1 (coin counter transistor) - replaced
  • Start 2 test point was missing - added it because I have them
  • Colors were off
  • Board was watchdogging
  • Cross hairs were leaving trails
  • Crystal was fine, the can was rattling - replaced it
  • Edge connector got cleaned up and liquid tinned. Copper was a little exposed
On first power up - board was watchdogging. Connected it to the CATBOX and ROM and RAM read good. Disconnected all of that and powered up again - still watchdogging. So I disabled the Watchdog.. board booted. Watchdog needed to be fixed.

Probing the watchdog circuit - the watchdog was not being cleared.. Working backwards..

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/WDOG was stuck high going into LS00@D8. It is generated by 7442@E8 Pin5. Replacing it fixed the watchdog circuit.

The colors were off. I determined that it was the BLUE and tested the R/G/B outputs at the video connector with the scope. Working backwards I found the following:

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Something that is pretty rare (at least for me).. R46 had drifted WAY out of spec. I could see good 'BLUE' signal going in and really bad signal coming out as compared to RED and GREEN resistors Testing the resistor, it read 2.8K ohms.. not 22 ohms. It was the original - maybe a monitor issue zapped it? Replaced it and colors restored!

The last item was color trails being left by the crosshairs...


This one I did a quick search and found a repair log Game board #16 and it looked nearly identical. One thing about this is it only started after the board warmed a couple of minutes - thermal failure. I sprayed it and some of the other chips in this area with Freeze Spray but the issue didn't clear.

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Repair log said replace the LS153@P7. Before that I did clip onto the chip with a tester and it seemed to effect it. Replacing the LS153 did nothing.. Below that is the LS251@N5. Probing that showed bad outputs on Pin5. I hit this chip with Freeze Spray (a little better than the first pass earlier) and the issue cleared. Replaced it and the color trails were fixed.

Board works!
 
Next Board - from the Arcade

Sent to me reported not working.. But it powered up for me. It does have a couple of issues that need to be addressed.

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This finger repair works - but the spacing between them is too close. The edge connector has a bit too much play east-west and can short between pins if not placed perfectly. On the bench it dropped the voltage down to 2.8v (on my meter). I will replace these so that it can't happen in the future. It may be why the board was reported not working..

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Board has a Braze kit and these RAM replacements. Both work fine - I did remove the Braze for testing.


The issue it does have is this color bar static below the text crawl. It changes depending on the colors directly above it. That area should be black and off the screen. Missile Command has a funny sync signal and I have to reset my LCD to get it on the screen in the first place, notice the lettering off the top.

The finger edge was bothering me...

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Removed the copper tape (which should have been soldered IMHO) and cleaned up the edges with Rust Erasers. They do the best job polishing up the metal. The second finger in was actually in good shape once I removed all of the goop from it.. Added fresh copper tape and used Liquid Tin to recoat all of the exposed copper.

The last part was finding the issue on the bottom. Missile Command has a strange setup on how it maps colors and treats the bottom 32 lines of the screen. This Website has some really good info. One new thing I learned is the Easter Egg diag modes (credit to the site above)

In self-test mode, there are some features not mentioned in the service manual:
  • Slam + P1 left fire: draw full-screen grid
  • Slam + P1 middle fire: draw color bars, erase screen, then exercise non-MADSEL read/write of video RAM
  • Slam + P1 right fire: draw color bars
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In diag - you can see the small vertical bars on the bottom and can cause them to rotate by hitting the fire buttons.. All that said - I spent a little too much time looking for the root cause..

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Probed all through this area trying to determine why I was getting color bits when they should have been off..

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However - when I finally went backwards a bit I found the issue (and it makes sense...) 7404@E6 pin 4 was not reaching ground. /VBLANK was sorta 1/2 working.. Missile Command has a lot of VBLANKS..

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Board works!
 
Awesome work. Got me to get mine off the shelf and get them sent you.
 
Love your dedicated control panel,
not used to seeing the trackball being on the left side of the 3 fire buttons...
Great info..
Either way it WORKS! GREAT JOB...
 
Yea - that controller was the second one I ever made - I have a bunch of different ones now.. It's not meant to 'play' the game so much.. it's meant to test it.. I've considered redrilling a new aluminum plate and moving it all around.. but there is no to reason as far as testing goes.
That controller is used for bench testing a bunch of games.. Anything with an optical controller I test with it..
Trackball games of course... but it also tests Tempest and Pole Position on the bench..
 
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