Space invaders deluxe Midway video issues

CanadianGamer

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I'm trying to help a friend with a space invaders deluxe upright arcade and I'm hoping someone can shed some light on the problems it's having. I'm attaching a video of the issues as well as photos of the boards. The video is in attract mode, and don't mind the background noise as there was construction going on. There has been some work done to it by the previous owner and has been this way since my friend bought the machine. He was told it was working, and just the score was a bit garbled, but obviously it's more than that. The RAM chips all look new, and have been socketed, and the ROMS have had some repairs done on them. My suspicions say the ROMs are the issue but hoping someone can confirm. I have tested the voltages on the boards and they are all good, and I have tried reseating the chips and connectors, all seem in good shape (aside from the rom chip repairs). Any help is greatly appreciated.

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This may be a long shot, but ages ago I had a similar issue that I thought was the board and is was actually the monitor. Swiping the contrast pot back and forth fixed it.
 

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Thanks for the input! I will try the contrast control since it's an easy thing to try first. I don't have a rom burner so I'd have to buy a test rom from someone, but I could try swapping out the LS 166 at C4.
 
I adjusted the contrast control, and did manage to get a little better picture, but still garbled numbers and text, and also not displaying characters properly. I don't know a lot about testing chips, but I put my logic probe on LS166 at C4 and there was pulsing on all the pins, either low or high. What should I be looking for when testing LS166?
 

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(Assuming the monitor is good) it looks like the DC blocking cap on the video out is leaky, giving an extreme HPF'ed look to the video.

...but I'd suspect the monitor first since there's far more analog stuff happening on that side.
 
I do have a scope Lurch, I'm just not very skilled at using it. What would I look for when scoping pin 13? Just check if it's flat-lining or wavy?

HudsonArcade, Would you mind clarifying the DC blocking cap on video out being leaky please? Am I just looking at doing a cap kit on the monitor? The scores and lettering etc being garbled just didn't seem like a monitor issue to me, but I'm not an expert by any stretch. Thanks.
You really need a scope to check if the signals coming out of pin 13 of the 166 are good.

(Assuming the monitor is good) it looks like the DC blocking cap on the video out is leaky, giving an extreme HPF'ed look to the video.

...but I'd suspect the monitor first since there's far more analog stuff happening on that side.
 
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there is a cap in series with the video output. it filters out a dc signal from the video output because if it charges long enough it will no longer allow voltage to flow. a video signal is alternating so it will pass through the signal. the cap could be bad or faulty thereby degrading the signal. the cap is on the main board. the signals coming out of c4 are standard pulses that turn the light of the monitor on and off. they are synched with the monitor scanning. there is a verticle and horizontal timing signal added in with the video to sync the monitor but that is working good. if you were good with a probe you would see pulsing with it and the sound would be decent a bad signal not hitting high and low would sound sick. I don't know how to describe it. the first time someone brought it to my attention and it was obvious.
 
a regulat tv with composite signal input can test the signal output. yellow rca jack. center pin hot outer ring gnd. this way you know if its signal or monitor
 
I usually never had to replace any caps on the board except tantalum caps. only twice did I have the filter cap go bad
 
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