Realising there is no documentation on the internet to calibrate these oscilloscopes.
I have a GOS 653G Or a (ISO-TECH ISR658G) and wanted to calibrate it. Note that powering up the unit will give better calibration results as the CRT warms up and the power supply reach a static voltage. Ensure this is the case before calibration.
I have identified 5 variable resistors on the cursors board. This is the board that is controlling the cursors drawn on the screen. There are some things one needs to be aware of when trimming these.
1. The cursors need to be at the extremities of the screen as these need to be aligned to the edge of the graticule.
2. These need to be adjusted with caution and in ratio to the zoom variable resistor located near the CRT tube ref.