Robotron CPU PCB--------Advice??

tec9

Active member
Joined
Dec 25, 2006
Messages
2,111
Reaction score
23
Location
New Britain, Pennsylvania
Hey all-
I got a Robotron machine that has a slight issue. It has a small amount of video garbage that is on the screen most of the time. The garbage is right below the border of the stages. The garbage is not on the screen during certain test modes, so I don't think it's a monitor problem. (monitor was rebuilt) The game does not report any errors, and plays fine. I did a quick swap of some parts I had lying around, and I have verified that the ROM board is good. It is running the original power supply and my voltages are close...about 4.94VDC, and -5V is spot on. I believe the problem is on the CPU PCB. I have swapped all the socketed chips on the PCB, and the video garbage remains. Any ideas or suggestions? I plan on buying the power supply rebuild kit, but was wondering what else would cause this?
-Mark
 

Attachments

  • 016.jpg
    016.jpg
    73.2 KB · Views: 37
What is this, a K4900 monitor? If so, adjust your V-LIN pot and see if that line moves above the border where it normally is. Sometimes (especially on monitors that haven't been capped lately) the image will fold over a little when the vertical size reaches the top. If the V-LIN pot doesn't help (or you don't have one), you can try decreasing the vertical size a little to see if that makes it move above the border. If so, then you can either live with it for now, or rebuild the monitor...
 
Thanks for the reply!
Hmmm....maybe your on to something. Now that I think about it, I didn't recall this machine having a problem, but never really played much with it, as it's been sitting in my shed for awhile. I decided to throw a cap kit in it, and that's when I noticed this issue. The monitor in the machine is a 4900, and it was just re-capped. I don't remember seeing a "V-Line" adjustment pot on the chassis, but I'll take another look. I also think that I have another working 4900 chassis sitting around, so I'll swap that in. I'll take another look tonight.
-Mark
 
Quick update:
I ran out to the shed tonight, and did some quick fiddling on the monitor, and it looks like it was a monitor issue. A quick adjustment made it dissapear, but I noticed it for a second during a different screen. Didn't have time to make a fine adjustment (it's cold outside!) but it should be resolved! It really looked like a PCB issue....glad it wasn't! Thanks!
-Mark
 
Back
Top Bottom