Perkin Elmer LC-55

[herbmaker]

I have a small self-financed home lab with lots of very old surplus instruments. I am also able to make basic refurbish work and also construct some new equipment. I have Perkin Elmer LC-55 spectrophotometer which I planned to use as VIS-detector in my HPLC system (now at 450nm); I have a separate UV detector. Now the baseline of the spectrophotometer is rising up all the time during the measurement even if there is no solvent flow on in the system. I think the problem is in the electronics. Could anyone give me suggestions which circuit component could cause the trouble? I know my question is quite specific but I ask anyway hoping that some old repair man could read this and give some suggestion based on practical experience.

[HW Mueller]

What is in the cell during registering this rise?

[herbmaker]

In the cell there is solvent. In this application 10%acetone in methanol. There is no difference whether the solvent is flowing or not.