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Colecovision AV Mod Help - Rolling Screen


Jeremy Popp
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DSC07171_copy.jpg

 

I built my own av mod after gathering info online based on the LM-318N. The mod generally works great, colors are great ETC. However, I tested Smurf the other day, and once I get past the colecovision screen, and game select, the screen starts slowly rolling vertically. Then I started testing other games, and it does it for Front Line, Pitstop and Turbo plus more. Seems like if there is scrolling in the game, I get rolling on the screen. About 75% games = no problems, 25% = roll.

 

It DOES NOT roll using my 51" plasma, but tested on 3 CRT's with rolling.

The above image is exactly what I made with a parts list as follows:

 

75 OHM Resistor (purple green black gold) 373-75 20 pc 0.49
(2X) 10k OHM Resistor (brown black orange gold) 373-10k 20 pc 0.49
AMP 134-LM318N 0.74 ea
47 uf 25 v capacitor 31-165 0.10 ea
10 uf 25 v capacitor 31-11338 0.10 ea
47pf capacitor 135-561R10TCCQ47 0.42 ea
PCB 21-4595 1.09 /pr

 

Also listed is the www.mcmelectronics.com part number. I have 2 colecos that do this, and neither one roll using RF. I also have tested with multiple power supplies with no change. Only conflict I can find in my mod is some call for a 27pf ceramic cap, and some say 47pf.

 

Any suggestions? I'm not an electrical engineer, but I love DIY projects like this, and I had a few spare colecos so i figure why not.

 

Thanks

Jeremy

Edited by Jeremy Popp
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I don't know which schematic you went with, the one I am using has 47uF from pin 6 of the op amp to 75 ohms resistor. Your board has 10uF cap on that spot. Maybe try swapping the 10uF and 47uF you have on 12v to ground rail?

 

Or did you have a schematic that has 10uF on video out and 47 on 12v rail? I'd like to see that one.

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I don't know which schematic you went with, the one I am using has 47uF from pin 6 of the op amp to 75 ohms resistor. Your board has 10uF cap on that spot. Maybe try swapping the 10uF and 47uF you have on 12v to ground rail?

 

Or did you have a schematic that has 10uF on video out and 47 on 12v rail? I'd like to see that one.

 

That did it! Amazing, thank you so much, I owe you one. I didn't have a schematic to go by, I just used pictures from the arcade componets mod and another similar mod. I thought I double checked everything, but I must have got them backwards because it works great now.

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Just FYI, there's another place to get 12v. If you did the DRAM mod and replaced with a +5v only version and removed the old inductor L2 and L3, one of the hole left behind is connected to 12v rail. Since it's easier to position the amp board in the area outside RF box, it might be easier to run wire to the 12v spot.

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