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Argus25 · 21st Jan 2019, 11:04 pm

I am not familiar with this particular computer, but other vintage computers such as early IBM's and the SOL-20 etc.

Most likely this is a RAM issue as the RAM IC's (at least in my experience) are a lot less reliable than the other logic IC's (typically 74LS series) that comprise the computer.

One thing to check initially is for any stuck low or high bits on the RAM IC outputs or any anomalous or intermediate logic states with the scope that should not be there. Also check the data & address bus for stuck bits. Also if the system RAM IC's and video RAM IC's are the same type, you can swap them around if they are in sockets, if you don't have any spares on hand.

A very good place to post your question, if you don't have any luck finding the fault, is on the Vintage Computer Federation/Forum's site where there are many people with the same computer that might have worked through the same fault before, it could save you a lot of time.

21st Jan 2019, 11:04 pm	#2
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: Commodore 64 Garbled Screen I am not familiar with this particular computer, but other vintage computers such as early IBM's and the SOL-20 etc. Most likely this is a RAM issue as the RAM IC's (at least in my experience) are a lot less reliable than the other logic IC's (typically 74LS series) that comprise the computer. One thing to check initially is for any stuck low or high bits on the RAM IC outputs or any anomalous or intermediate logic states with the scope that should not be there. Also check the data & address bus for stuck bits. Also if the system RAM IC's and video RAM IC's are the same type, you can swap them around if they are in sockets, if you don't have any spares on hand. A very good place to post your question, if you don't have any luck finding the fault, is on the Vintage Computer Federation/Forum's site where there are many people with the same computer that might have worked through the same fault before, it could save you a lot of time.