Asteroids Deluxe board problem with video

wolfeel

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I have an Asteroids Deluxe board with some issues that you can see in the video.

http://www.youtube.com/watch?v=srJTHlRvxeM

I put it in a tested and working cab. All chips look clean. I will try to pull, clean and re-seat. If that does not work could anyone give advice on where to begin? I have a DMM, Logic Probe and will have an Oscilloscope soon.
 
I am positive it is not a monitor problem or anything else other than a board problem because I put the board in a tested and working machine. Just to clear the video up you will see it in normal mode first (I was playing it) and then I switched to test mode and then you can see me play with the x and y pots on the board.
 
Pulled, cleaned and re-seated all socketed chips with no change (the all looked very clean). Board looks to be recapped. Just to make sure tested 5V on board and found 5.08 VDC.
 
You've got foldover....I'd start by checking out the video output section, specifically the "Y" side. Maybe a bad 4016.

Edward
 
You've got foldover....I'd start by checking out the video output section, specifically the "Y" side. Maybe a bad 4016.

Edward

I 2'nd that. Also check for -15V at the Y DAC. If it were missing bits, the video would either skip sections or wrap around. Yours looks like it's all there but just goes the wrong way after reaching the center line. That points to a loss of voltage scale, hence the -15V may be missing. Find the 7915 3-pin regulator. It may be really hot. Either something on the -15V side is shorted and overloading the 7915 or it's shot.
 
Well I am on the right track because your guys advice is where I was heading. I thought the problem existed in the video output section but I was not sure which section, X or Y. After reading your guys advice and thinking about it for awhile it does make sense that I would be missing -Y information, causing the -Y image to fold over the X axis.

I believe I have found chip B12 (a 4016B) bad and this is how I found the bad chip:

With the board out of the machine I set my meter to test for junction drop, grounded the red lead and looked at the junction drop on the pins of each chip in the X and Y video output sections. I looked at matching chips in each section and found that a pin on B12 did not have junction drop while the matching chips pin in the other section had junction drop. So I am assuming I have a faulty chip at B12. Was this a correct way to test the chips? How else do you guys test chips?

wysiwyg2:

Thanks for the advice on where and what else to check. I am away from home but when I get back I will try testing some more.
 
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