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[Reply #15 on:]

I can see why the contrast adjustment doesn't work. The Vo pin is not connected on your board because jumper J1 is open (same as on mine), but unlike my board, yours does not have the 10K pot - although the pads have been tinned as though it should have been fitted. Similarly, the Vout pin is not connected - it goes to the resistor at position R12, which is not fitted.

The best suggestion I have is to source a pot of the correct size to fit at VR1, and remove the 0 ohm resistor R6 which is shorting it out. The pot on my board has a resistance of 18K end to end but is set at 2K. So a 10K pot (which is what the ST7920 datasheet shows) would be fine.

[Reply #16 on:]

Thank you for the help, at least now I know (more or less) why the contrast is not working. The contrast is btw enough ok, also I'll think if it's the case to made these mods. Important is the backlight is working and I don't need other resistors.

Thank's a lot for the support!

Simon