Been there, done that. With no manual. Here's what I did. My 7603's image
became horribly distorted and "weird" looking. The sides come off easily;
lo and behold: nearly all signal points are labeled. I checked the power
supply voltages and found they were a little off. So I checked it with a
different scope and found 120Hz riding on all the supplies.

After paying an hour or two to the troubleshooting gods, I found one of the
main filter caps in the supply had opened up. It happened to be the
particular supply that all the other supplies used for a reference thus
causing the 120 Hz to get into everything. Replaced the cap, back on the air.

No manual. Just some time spent pondering.  On the 7000 mainframes,
*everything* has a connector so it makes it far easier to troubleshoot. So
have faith; you might get lucky and be able to find the culprit.

Good luck!
Tom M.

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