82162A Printer Contrast Redux



#2

Some time ago I sought advice on the print contrast of my 82162A printer.
(82162A Printer Contrast)

I am happy to report that I have finally figured out what the root cause was for the poor printing and was able to fix it. I am posting the solution here for completeness of this issue should anyone have a similar problem in the future. The problem was with the Resistor pack 1810-0540 that is used to control the output voltage of the power supply to the print head. Using the schematics that Tony Duell had created, I was able to figure out where to measure some of the voltages at several locations and I was also able to determine that I would be able to measure the resistance values of the resistor pack that feeds back to the power supply. As I was repeating my measurements, I notice that the output voltage had increased. I then did a quick print test and now the printer was printing correctly with the proper contrast. I was thrilled at this point. Figuring that I did something to the circuit board, I carefully inspected the components I tested and found several cold solder joints on the 180-540 resistor pack. Apparently, the action of testing these joints created enough of a connection to make it work properly (at least for a while). After a little de-soldering, cleaning, sanding, some flux and a little more solder, the printer functions good as new.

I like to slay my own dragons and I derive a good deal of satisfaction when I have success. But I don’t think I would have had success this time without the schematics from Tony Duell. They were invaluable to trouble shoot this problem. So, thank you Tony.

Tom F


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