OK. so it was really, really messed up!!!
Display kept getting dimmer, and dimmer, and then got to the point that no matter what I did I could not get ANY display at all! I started worrying the CRT was failing, and died. But no! Did NOT adjust the CRT bias or touch anything in the CRT ckt. at all.
I checked all the PS DC voltages. Spot on. Then tried to adjust the DAC per the adjustment section in the svc man. It would not adjust to the 2.5 volt total range, and kept getting worse, and worse! Studied that bridge ckt. with the adjust pot, found R2013 10k COMPLETELY open. There was a small amount of electrolyte leakage from the caps, but this area looked perfect! No idea why that resistor would open!
So to my surprise this fixed not only all the brightness issues, but also many other problems that I was certain were going to require a complete CAL. NOT SO!!! DAC adjusted just fine. Everything seems to be working now!!! Previously amplitude, and Freq measurements were pretty far off. I'm so pleased to get this baby runnin' like it should be. About $300 and a little troubleshooting. Yippeee!
Thank you all so much for your support, and guidance. Reassuring to get informative replies. Thanks!
Martin