Colecovision Video RAM Issue Help?

[+KylJoy]

I am not 100% positive but I believe I have a video RAM problem in a Colecovision. Here are two images:

 

During a blank screen interval:

 

Following the VRAM test of the diagnostics cart:

I have performed a 5v Video RAM replacement in other ColecoVisions and don't want to do that right now. I just want to get this unit fully working for now.

Can anyone tell me if there is a way to identify which RAM chip(s) is(are) bad from the images or a good way to test each chip?

Thanks!

[Ruggers Customs]

Logic probe or an oscilloscope.

 

 

Here's the datasheet for the 4116.

 

https://console5.com/techwiki/images/8/85/MK4116.pdf

[Ikrananka]

Wow - that's interesting graphic corruption - never seen one quite like that before. Wish I could help.

[+-^CrossBow^-]

Could this actually indicate an issue with the video processor chip itself and not necessarily the vram chips? I've not seen this kind of corruption either.

[+KylJoy]

Could this actually indicate an issue with the video processor chip itself and not necessarily the vram chips? I've not seen this kind of corruption either.

It's a lot easier to socket and replace that one IC so I might try that and see if the issue clears up. But I'd still appreciate it if someone could point me in a very specific direction.

[+KylJoy]

Well, I totally lucked out and replaced the only bad RAM chip with the first socket I installed. It was U17.

 

Here is a pic of the socketed RAM:

 

I used a spare RAM chip from a console that I performed the 5v RAM upgrade on in the past. It is interesting to me that two different brands of RAM were used on the motherboard previously. It looks like original work so I am guessing it was original like that. Anyone know differently?

 

Here is how the screen looks now:

 

[Ikrananka]

Congrats on the fix. Interesting to know that a faulty VRAM can cause that kind of graphic corruption.