Adjusting R8 to Increase HP-97 Printer Intensity

[teenix]

(02-17-2021 04:33 AM)James Linder Wrote:  I ordered the PCB mount potentiometers. I see they have 3 connectors.
I see 1st or left terminal is to be grounded, middle #2 is input and right # 3 is output to PCB. In the pictures showing R8 which end is the output from R8 that is Input to #2 of the potentiometer? Also, where would the most convenient ground be located for terminal #1 of the potentiometer?I’m just a beginner on circuits and want to make certain that I do not screw up the installation. Do you think increasing resistance is guaranteed to increase print intensity? I bought some 50k ohm potentiometers in addition to the 20K’s just in case I need to add more resistance than 20K to achieve the desired results. Thank you very much for your help!!

Connection diagram attached.

The pot will use 2 connections. One from any end terminal, and the other the center terminal.
Unsolder one end of R8 and connect it to the pot end terminal via a short length of wire.
Solder a wire from the pot center terminal to the PCB hole where the R8 connection was unsoldered.

When you get the correct contrast on the printer by adjusting the pot, unsolder the pot wires, measure the resistance of the pot between where the wires were. Measure R8 resistance and add the two values to get the required resistor value.

As resistors come in certain ranges of values, you may have to choose the closest one.

A 1/4 or 1/2 watt type will do.

cheers

Tony