Adjusting R8 to Increase HP-97 Printer Intensity

[teenix]

(04-01-2021 02:15 PM)James Linder Wrote:  After trying different things I now just replace R8 with a new 200K ohm resistor in every HP desktop I restore and this always results in a high quality, dark print quality. It’s wasted effort to play around with other resistance values when just installing the maximum resistance HP lists in their service manual is a sure thing!

I would be checking the print head PWM signal at this setting just to check the mark space ratio. If HP installed a much lower resistance in a particular unit , then there would have been a reason.

It also might be a different component that aged causing the faded print, but this would be hard to test as it will be encapsulated on the printer's analog board. Myself, in this case, I would put up with a slightly faded printout. I guess the analogy is I wouldn't drive a tired and slow old car flat out all the time, it wouldn't last ;-)

cheers

Tony