PeakTech 6225 Lab PSU with a drift problem

[YadiYada]

I set this PSU to a voltage (tried different starting points: 5V, 12V, 15V or 30V) and a load of 200mA or 2A.
The originally set voltage drifts down by about 120mV over the course of 20-30min or so. I have two of these PSUs and they do the same.
Any clever ideas on how I could "fix" that? Including schematic for reference (I know the schematic shows MCH-K305D but that seems to be the OEM's).

[ArthurDent]

The schematic you show is not for the actual power supply but just for the metering section of the supply. The two leads that go from CN0 on the top left then down between the V/A metering sections are the inputs to the meters that would connect to the sensing area of the actual supply which isn't shown. There should be more schematics.

[YadiYada]

The second page of the attached PDF is showing the main diagram.