This preamp was humming and some of the graphical sliders worked as a noise generators rather then equalizer. Also the two momentary switches were bad. I couldn’t find the exact momentary switch so i had to modify the switch cap slighty to fit modern replacements.
Re-cap and upgrade of main filter cap from 2200uF to 15000uF resolved all the PSU induced hum and one of the transistors in the graphical equalizer actually had a small crater where the silicon chip used to be inside of the plastic casing. It was interesting that the transistor was still working-ish but it was acting as a noise generator.