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Printer and Photocopier Troubleshooting and Repair Collection : HP LaserJet III paper feed problem      
 Copyright © 1994-2007, Samuel M. Goldwasser. All Rights Reserved. Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: 1. This notice is included in its entirety at the beginning. 2. There is no charge except to cover the costs of copying. I may be contacted via the Sci.Electronics.Repair FAQ (www.repairfaq.org) Email Links Page.
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HP LaserJet III paper feed problem

My LJIII wouldn't feed paper past the registration assembly. Sounds like a mechanical problem right? No, it was not mechanical but rather it was electronic problems. At first I replaced the two drive transistors on the solenoid board thinking that one of them burned out but that didn't solve the problem.

Then, the whole thing came apart as I traced the connections for one of the solenoids back to the DC controller board. Guess what? One of the PCB traces near the 78324 IC (large square one) was corroded away. I quickly soldered a wire across it and now it works perfectly! Now I wonder what could have caused that...?