I have been working on a non-functional 485 that I picked up. I discovered that the inverter was cycling rapidly on and off. I resolved an issue that was shorting out the +15V power line, which restored all power supply voltages to their correct levels.
Now, the trace is very bright (enough that if it is moved down onto the screen, it will occasionally trip the protection circuit and cause the power supply to cycle). The intensity control has no effect.
I have checked the DC restorer diodes with my DMM - all appear OK.
Would anyone familiar with this type of problem be able to advise next troubleshooting steps?