TEK 2465B schematics or error code check list needed

Hi all, I have a Tek 2465B that stopped operating. I turned up the 'grid bias' and can read 'Test 05 Fail 42' at the top of the screen. I have a manual, but without schematics or troubleshooting flow guide. The manual indicates the error code is for the main board positive level too positive. I've checked the low voltage supplies and all is within spec. Schematics, error code indicated potential problems or other help is appreciated