HP-97 Printer Malfunction

[Paul Berger (Canada)]

Hmmm Very odd, the only thing I can think of that would make a whirring noise in the printer would be the motor however you say it will not move in the forward direction. If the paper feed switch is incorrectly wired it can affect the forward motion, but only if you do not have paper in the printer. With paper in the printer the end of paper switch (OPS) would be open isolating the forms feed switch from the forward line. One thing that occurs to me is if one of the transistors that energize the motor in the forward direction is marginal and does not supply the motor enough power to move it forward but it moves easily when you give it a little push. You could try removing the middle idler gear and see if the motor moves under no load, also if you can hear a hum you may want to put your finger on the motor to feel for vibration. When you are manually moving it in the forward direction it probably energizes it in reverse when the home position switch drops out.