I had similar problems with my ESQ-1 a few years back. every 8th key would go out intermittently. I opened up the top panel and took out the keyboard assembly and gave it and the inside a good once-over, and it's worked fine. You may want to try an electronic component cleaner (stuff in a can, available at a computer store) and spray it on some of the contacts. Wee bits of dirt can raise havoc in those old boards.