Missile Command V Blank error in test mode only

TrevEB

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Oakland, California
My missile command appears to run perfectly fine until I switch it into test mode.
The test begins but then halts with a flashing screen and raspy tone indicating a
v blank error.

See Video
http://www.youtube.com/watch?v=oApIPJgT994

There are no visible signs of damage to the board. In fact the board is remarkably clean.
I've tried pressing on the corner socket chips with no effect.
The chips are very firmly in place and will tear the socket apart
if I attempt to remove them.

The voltages all test out perfect.

Is this problem indicative of an eventual failure during game play mode.
Is the problem isolated to the game board?
The schematics show references to vblank at
E6, H7, J6, L8, M9

I've only owned this machine for a few weeks.
I don't believe that it has ever passed the system test.
While I've owned it, I have replaced the caps,
rebuilt the trakball and replaced the bulb & starter.

Any suggestions on how to remedy the problem?
 
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I don't think that's a VBLANK error. It looks like one of your switches is stuck closed. Look at your slam switch, player starts, coin switches, and fire switches.

Note that you can narrow your search by observing the gameplay, i.e. if there's no screeching during play then it's probably not the slam switch. If you can coinup with both slots then it's probably not the coin door switches. Etc...
 
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I have worked on my switches, but will take a closer look at them.
currently during gameplay:
slam switch no screeching
both coin doors work
both player 1 and player 2 flash and start.
all 3 bases fire properly, but I may have fouled up the wiring while mucking with them.

2 of my base switches have red leds and one has the proper black switch.

The slam switch should be open. no contact between the leaves. I slipped a piece of tape in there to keep it quiet when I open the door during work (with the safety switches taped shut.)
I know it stays quiet with the tape is removed and screeches when triggered.
 
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There is a third coin door switch input. On an upright it's left unconnected. If you have a voltmeter you can check it at pin 2 of R49.

Also check the three player 2 fire inputs. You can check voltage at J19 pins D,E, and 5. Alternately you can check pin 2 on R52,48, and 53. If one of those reads close to ground, it's possible that one of the capacitors C95,97,or 96 has shorted. Also possibly a bad LS191 @ K9.
 
Bit Slicer, you were correct.
Thank you!
I had reconnected the 3 base switches incorrectly.
In test mode, the three buttons acted like they were being held down all at once.
Easy fix and everything works great now.
 
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