I've been doing a lot of power cycles on my SOL-20 recently as I've been trying to bootstrap Northstar DOS. My SOL has been problem free for quite some time, and strangely enough I was just thinking how luck I had been when about 30 mins later I powered up my SOL only to be greeted by a blank screen!!!

neoncluster.com

The problem didn’t take long to fix. Less than an hour. It was the 74LS163 @ U40 in the video circuit. It's great having everything socketed, because if you can get a general idea where the problem is using a logic probe, and have a good supply of logic chips, I just do quick chip swaps until I find the problem. It's cheating a little, and doesn't always work, but when it does, it's fast and efficient.