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Colecovision Video RAM Issue Help?


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#1 KylJoy OFFLINE  

KylJoy

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Posted Thu Oct 11, 2018 10:07 PM

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:

20181010_194039.png

 

Following the VRAM test of the diagnostics cart:

20181010_193828.png

 
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!


#2 Ruggers Customs OFFLINE  

Ruggers Customs

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Posted Thu Oct 11, 2018 11:52 PM

Logic probe or an oscilloscope.

 

 

Here's the datasheet for the 4116.

 

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



#3 Ikrananka OFFLINE  

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Posted Fri Oct 12, 2018 10:14 AM

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



#4 -^CrožBow^- OFFLINE  

-^CrožBow^-

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Posted Fri Oct 12, 2018 10:17 AM

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.



#5 KylJoy OFFLINE  

KylJoy

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Posted Fri Oct 12, 2018 4:46 PM

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.




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