Sony Monitor KX14CP1-SM boosting G2/screen voltage does not change brightness

[terryfi]

Hi everyone,

I recently acquired a Sony Monitor KX14CP1-SM monitor. It is a multisystem, composite and digital and analog RGB capable monitor.

I opened it up for servicing and noticed when I adjust screen pot the screen brightness changes a bit but immediately the feedback circuit will turn it back down. So I can't notice any change of brightness with lowest and highest voltage setting with exception of some trace lines at maximum. I have verified the pot is working G2 voltage changes between 270V to 630V within spec.

The focus knob works well I measured the its voltage at 670 volts, everything else is ok, I have reflown the solder on neckboard. The R G B driver voltages are within spec. The picture knob is maxed out. I also measured the R G B input voltages at TDA3505 (RGB interface chip) they are all above spec'd voltage of 5.9v.

Appreciate everyone's comments and suggestions.

[terryfi]

After looking at service manual I see some probably X-RAY protection circuit involving HVR, maybe that is kicking in?

^^ Correcition, I don't think HVR is related to XRAY protection for this specific monitor, the pot for CV actually is H.STAT to change the converge RGB horizontally.