Missile Command help needed

[GearHead]

I have a cocktail version of Missile Command that was working nicely but now that I'm considering selling it the machine has decided to give up on life.  Before I start opening up the machine and poking around I was hoping someone here could help diagnose the problem.

The machines turns on and displays this on the screen.  I reseated all the socketed ICs and hit the edge card connectors with an eraser to clean them up.   Any thoughts?  Thanks.

[SirPeale]

What are the voltages?  I assume you have checked them with a digital multimeter.

[Q*Bert_OP]

 big blue?

[GearHead]

Peale,

Yep, I checked all the voltages at the test points on the board.
I get the +12, +5, -5.  The 10MHz and 5MHz clock signals are good too.

I'll check out the video sync levels later.

Q*Bert,

What do you mean by big blue?

[Q*Bert_OP]

Big blue is a very large capacitor(about the size of a coke can), located near the x-fmr block, on the metal plate in the bottom of the machine.

It can cause all kinds of wierd problems.

[Havok]

They are notorious for failing in Atari cabs. Bob Roberts sells them:

http://therealbobroberts.net/parts.html

And, a little bit of info about them:

http://therealbobroberts.net/bigblue.html

[Kevin Mullins]

Does the game play "blind" ?
Will it coin up and start a game with sounds and such going on even though you can't see it correctly ?

And does the Missle Command have a TEST or SERVICE switch in it ?

[RayB]

Since your voltages look good, I doubt the big blue is at fault (though I am no expert -- I am just assuming that the AC coming IN must be right, if the DC going OUT is right...)

Flip the test switch on, then power up. You will hear some beeps and noise indicating the status of your RAM chips, etc.  The manual will tell you what the beeps mean.

Also clean the board edge traces and make sure the harness is on tight.

[grantspain]

looks like a graphics ram fault to me,its a long time since i have seen one but did'nt the z80 chip cause faults like this

[Q*Bert_OP]

looks like a graphics ram fault to me,its a long time since i have seen one but did'nt the z80 chip cause faults like this

It's possible...

[GearHead]

I looked at all the DC voltages with a 'scope and they're smooth and clean.  This might rule out Big Blue being the culprit.

The game does not play at all.  Test switch up or down yields the same result - nothing.  No sound or change in the display.  The processor could be it.  Maybe the clock crystal?  I'm getting more of a sine wave than a square wave out of the 10MHz test point.

Any more suggestions?

Thanks.

[Q*Bert_OP]

CHeck your processor, I'm not sure about your crystal...