I'm out of interesting stuff to try and fix so I started on a commando board I dumped in my 'can't be bothered' pile.
It's only issue is horizontal blocks and my first thoughts was a ram issue.
I decided to just started probing around the ram at 2b on the top board. It didn't take long to find a problem, the 3rd output at pin 9 on the ls157 @ 1b was showing random activity, so I pulled it out and threw it in the tester.
I took a quick look at the schematics just to see what the faulty output gate (pin 9) was responsible for, leading to the ram.
I had some new 157's so I replaced it and happily it fixed the issue.
Shinydaz2018-07-15 01:46:17
It's only issue is horizontal blocks and my first thoughts was a ram issue.
I decided to just started probing around the ram at 2b on the top board. It didn't take long to find a problem, the 3rd output at pin 9 on the ls157 @ 1b was showing random activity, so I pulled it out and threw it in the tester.
I took a quick look at the schematics just to see what the faulty output gate (pin 9) was responsible for, leading to the ram.
I had some new 157's so I replaced it and happily it fixed the issue.