ColecoVision Issues

[EmOneGarand]

Just got a Colecovision I won on Ebay, it runs but it has vertical lines running through the couple games I tried, tried cleaning the games didn't fix the problem. I read somewhere that the power supply is finicky and could be causing this, anybody know anything about this? Thanks.

[Bruce Tomlin]

While people talk a lot about the power supply, the real power problem is the power switch. The grease in the switch (which keeps the contacts from oxidizing) was crap, and in approximately 100% of the units manufactured, it turned to gunk more than 10 years ago. The oxidation reduces power to the circuitry, especially to the finicky 4116 DRAM chips used for video. And it's a lot of work taking one of those things apart to rebuild the power switch.

 

Also, the 4116 DRAMs are known to fail. If the startup screen has incorrect letters, that's not only a sure sign of a DRAM problem, but can even tell you which chip to replace.

[EmOneGarand]

While people talk a lot about the power supply, the real power problem is the power switch. The grease in the switch (which keeps the contacts from oxidizing) was crap, and in approximately 100% of the units manufactured, it turned to gunk more than 10 years ago. The oxidation reduces power to the circuitry, especially to the finicky 4116 DRAM chips used for video. And it's a lot of work taking one of those things apart to rebuild the power switch.

 

Also, the 4116 DRAMs are known to fail. If the startup screen has incorrect letters, that's not only a sure sign of a DRAM problem, but can even tell you which chip to replace.

Weird, the games I tried did not show a startup screen, there was just a blank screen with a delay before the game would boot.

[Bruce Tomlin]

That possibly indicates that the high bit (D7) of DRAM is stuck high. This would also cause a vertical line in every graphics cell, but the line should also show in the missing startup screen as well. Whichever is the lowest numbered DRAM chip is D7. (and D0 is the highest numbered chip)

[EmOneGarand]

That possibly indicates that the high bit (D7) of DRAM is stuck high. This would also cause a vertical line in every graphics cell, but the line should also show in the missing startup screen as well. Whichever is the lowest numbered DRAM chip is D7. (and D0 is the highest numbered chip)

Should I see about replacing that DRAM then? I'm about to modify my console for A/V and since it's supposedly a pain in the ass to get open I should fix things while it's open Where could i get a replacement for the DRAM?

[EmOneGarand]

is this the same kind of DRAM used in the colecovision?

 

http://www.mikesarcade.com/cgi-bin/store.pl?sku=RAM4116

[EmOneGarand]

Nevermind, the AV mod fixed my graphical problems though I'm getting quite a bit of bleed and interference with the picture, I think all my grounds were secured...