I got the PC-3100S quite a while ago and it *mostly* worked, it powered up into BASIC and you could throw direct commands at it and have it fire back at you, but something was wonky about the way it was storing program lines. You can check for more details about that in the main PC-3100S system article.

The primary suspect was bad RAM. I sent it off to my friendly repairperson for a health check and repair. It was indeed a bad RAM chip, and it now works beautifully!

In addition to the RAM chip replacement, he recapped the entire machine for hopeful longevity, and also built me a custom video cable so I can use it either with the dedicated monitor or plug it into any ol' composite video input-wielding display for more flexibility (photo upload impending).