HAMEG HM303-6 Remove Panel Knobs

[2X]

Hi,
I have the HAMEG HM303-6 oscilloscope and I want to remove the front panel in order to clean it and to clean the screen inside (it seems there is a drop of oil or something like this).
At the below service manual writes "Turn the 3 variable knobs (arrow marking) from their calibrated detent to a position..." what is the "calibrated detent to a position"?

At the page 16 writes:
"Note! Before inserting the variable knobs shafts, check that the potentiometers are in calibrated detent position. Thereafter insert the shafts completely and turn the variable knobs clockwise until the arrow symbols point to the right. Then fasten the shafts using the hexagon sockets accessible in this position. Turn the variable knobs counter clockwise (ccw) until the unfastened hexagon sockets can be fastened."
The potentiometers (page 17) must be calibrated only if a PCB replaced or even if a board removed and reattached again?

Also, for the cleaning of the screen can I use an isopropyl alchohol or glass cleaner or there is a deticated cleaner for these screens?

[TaylorD93]

Not sure if you ever worked it out,

beside each Y attenuator switch there is a symbol showing the "calibrated" position, in this case you would need to rotate the vernier Y axis pots (not the rotary switch itself but the knobs you have removed for your photos) to the 3 o'clock positon.

It looks like that wording is for the older versions of HAMEG scopes where a lock nut is hidden inside the Y axis knobs. On your model, to remove them you need to first remove the vernier rods, they slide through the front panel and switches and there is a flex coupler inside, so to remove the facia, for each knob with a vernier adjustment you need to loosen the rods. then they slide out.

Technically you dont need to remove the knob from the metal shafts you have photographed. Once the flex couplings are loose, the metal rods slide forwards and then you can slide off the larger knobs. be careful they sit on a hollow plastic shaft that is part of the switch itself, if they snap you are in a world of pain to glue them back together reliably!