Robotron - weird horizontal lines

debaser138

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I've got a Robotron where the CPU board failed to boot. I picked up another working Robotron board and the game is working but I'm getting a couple of static horizontal lines across the upper part of the screen. They are always there, except on the RAM, ROM and CMOS test screens (all of those tests pass fine).

I've upgraded the RAM to 4164 but that didn't change anything.

Any ideas on what this could be?
 

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Those look a little like the line at the top of the screen. Have you tried adjusting the vertical size? There is an adjusting screen in the diagnostic to set the horizontal and vertical width. Try bringing up that screen and see if the vertical size is too big as it sometimes will curl over and ghost back on the screen.

ken
 
Yes those are normal and the other board had them in the exact same spot. You have to adjust the chassis pots so it puts those lines just up enough to hide them under the bezel.
 
Rob,
I think you're thinking of the vertical lines on the right, those are normal to Williams games and can be adjusted so they are just off the screen. I think he's referring to the horizontal 'dashed' lines across the top quarter of the screen. They flash, blink and move around a bit, especially during attract mode.

I had the same problem with my Robotron (G07 monitor), which started to do it a few years ago, and gradually got worse. Since the symptoms worsened over time, I figured it was monitor-related. I did a thorough rebuild on it, including new caps, which fixed the problem.
 
The horizontal dashed lines are an artifact of the video circuit. There was some discussion of this at length a while ago. Apparently they can be eliminated by putting a modification that appeared in later MPU boards which delays the video circuit starting to generate the video signal by a couple of milliseconds.

What debaser is seeing is that very topmost line with the garbage curled around slightly. Think of the screen as a flat sheet of clear plastic. If you push the plastic up too high, it will curl over and you will see the image reversed and upside down. The cure for it is to either reduce the vertical size and reset the vertical position (which is what the grid screen in the diagnostics is for) or to do a capkit and then reset the parameters for the display.

ken
 
Rob,
I think you're thinking of the vertical lines on the right, those are normal to Williams games and can be adjusted so they are just off the screen. I think he's referring to the horizontal 'dashed' lines across the top quarter of the screen. They flash, blink and move around a bit, especially during attract mode.

I had the same problem with my Robotron (G07 monitor), which started to do it a few years ago, and gradually got worse. Since the symptoms worsened over time, I figured it was monitor-related. I did a thorough rebuild on it, including new caps, which fixed the problem.

Nope I meant the ones on the top. I had to mess with the pots to get it up to the top of the screen.
 
Wouldn't the score be cut off then? We must be looking at different lines.....

Have you never seen curl at the top of the screen? If you adjust the size of the screen the lines at the top will "curl" over the top and start to slide down the screen:

Code:
  ___
 /   \ ----------------- top of viewing area
|    |
|
|
|<--------------------- image on screen
|
|

By adjusting the vertical size and the vertical position the image that has folded over will get pulled back into its normal position at the top of the screen.

ken
 
Have you never seen curl at the top of the screen? If you adjust the size of the screen the lines at the top will "curl" over the top and start to slide down the screen
Yup absolutely, I just didn't see any foldover in the picture debaser posted above.
 
Just to clarify, I'm not talking about the artifacts on the right hand side of the screen. I know those are normal. I took the picture before I adjusted the monitor so those are not visible.

It's not foldover. I've attached a picture of the crosshair screen.
 

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Same issue here

I have the same issue here. Robotron looks and plays great but I get these freaking lines that come on and off and don't know how to cure it. I have a 4900 monitor. If you go into the color bar test it looks like the bars are bent at the top. the grid looks normal though.

Let me know if you or anyone come across a fix for this.
 
Stargate does the same thing. Just adjust your vertical size smaller, and those will move further to the top, to the point where you can hide them.

Yellow dog has it correct.
 
Foldover means it's time to recap the monitor if you can't adjust it out.

Since it's the VERY top lines in the picture it will fold over and onto the grid without disturbing the grid itself.
 
Fix

O.k. I think I know the fix. It's a pain in the ass though. You would have to adjust the horizontal width to make the screen small enough where those lines would be on top of the high score. Now, the picture will be a lost smaller and as soon as you even try to increase the horizontal width those lines shift below the high score.

The fix:

Adjust the horizontal width until those lines are well above the high score. The picture will be a lot smaller and it won't fit the screen.

Next, you'll have to discharge the monitor and remove the chassis. This is a WG 4900 that I'm working with. C365 cap position is the Horiz width cap which will need to be changed to a
different value so it will expand the screen to hide those lines. The capacitor that will needs to be used is Polypropelyne (Bob Roberts sells these). The best method of testing which cap will work best with your chasssis / tube is as follows:

Make a double ended alligator clip wire. At position C365 you'll need to remove the cap at this position and solder in two posts so you could clip one alligator clip on each post. On the opposite end alligator clips you'll need to dry different size polypropelyne caps to see if the picture gets better or worse. Once you find the right cap and the screen expands properly, those lines should go away.

Here is a list of Horizontal width cap locations for different monitors from Bob Robert's page:

* Common Width Cap Positions
* Wells-Gardner K4600 Series - C615
* Wells-Gardner K4900 Series - C365
* Wells-Gardner K7000 Series - C38
* Electrohome G07 - C515

The Bob Roberts link for the horizontal width caps page is as follows:

http://arcadecontrols.com/BBBB/width.html

Now to test this method myself. However, I'm confident that it should work for all.
 
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