Space Invaders off of Detroit CL

CMAC

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I picked up a Space Invaders off of CL a week ago. Here are the original pics:
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The good:
Cabinet/side art/coin door/control panel in pretty good condition.
Planet/white-black light/backdrop all there and working.
Plays with video and audio output.
Insides are very clean and all original except for the speaker.
Looks like it never had the wood skids taken off and feet installed. They have cabinet paint on the ends.
$75.

The bad:
The bezel has been cracked and taped back together. You can see it in the ad picture but it's much worse in real life. Has to be replaced.
Monitor has vertical collapse.
Bass sound is distorted. Could be because the original speaker has been replaced with a car speaker (4 ohm).
Top back door is from a different SI. Didn't come with a key and somebody cut out the wood strip from the right vent to get inside?
Bottom back door is missing. The classic repair had been made to the back door switch - taping it down with nasty sticky electrical tape instead of simply pulling it out.

I'll post more pics later.
 
After playing with the yoke connectors the vertical collapse has been fixed and I have a nice image. Disconnected the car speaker and hooked up a 8ohm speaker - sounds (especially bass thump) are all still distorted when volume is turned up at all. Bass is always distorted. Any ideas on fixing this sound problem?

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OK, so I'm trying to measure the +18V which is responsible for sound amplification (+5, -5, +12 all checked out OK). Measuring across the 1000uF capacitor (I assume by placing a lead on each end of the cap) on the power supply I get 15.08V. Measuring on pins 10 & 11 of the 16 pin connector on the daughterboard I get 9.97V which when the game is being played and sounds are being produced drops as low as 1.95V. So it looks like this is my problem. Am I correct in assuming the 1000uF capacitor on the power supply is the one failing and leading to the unsteady voltage? Should I be looking at something on the daughterboard instead?
 
Well, mine was indeed the power supply. I replaced all 4 of the A14 diodes with 1N4007s and the 1000MF 35V electrolytic cap in the little sound voltage circuit area below the connector jack. I left the 1N4004 alone. One of the A14s was bad and one of the leads from the cap was coming loose from the end of the cap. Now all the sounds are great.
 
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