How to clean a printer?

by Ben Ong

PC100A/C is a robust device, which operates like a line printer (and therefore much faster than HP's printers for the hp-41 series).  However the most common problem for this printer is that (due to age) the print-out is not very consistent (some characters can be read easily while others are faded). I recently opened up the printer and found a solution to solve the above and I like to share my experience... The main reasons that the printed characters are inconsistent are:

bulletPrint head dirty.
bulletInconsistent pressure of the metal print head against the rubber roller.  

To correct the above, proceed as follows:-  

bulletOpen up (disassemble) the printer.  There are three tapping screws at the botton of the printer and two in the battery charging compartment.  Once you have removed the screws, the upper half can be seperated from the lower half.  IMPORTANT - There is a wire that connects between the lower half and the upper half and therefore do not seperate the two halves physically, just move the upper half away slightly to allow enough room to access the print head mechanism.  
bulletPrint head cleaning.  Unlatch the spring that press the metal print head agaist the roller to release the print head mechanism.  Be very careful here because the pring is under high pressure and note the positioning of the pring correctly so that it can be fitted back easily.  Once the spring is detached, you can move the print head mechanism loose enough to get a close look at the printed circuit of the print head.  Clean it carefully with soft cloth/alcohol and reassemble the spring.  At this point, you may wish to adjust the spring slightly to give more pressure on the rubber roller.  
bulletInconsistent printing.  Use 2 small springs (normal battery holder springs, etc) and fasten one each against the two black tapping screws at the corner of the metal print head mechanism.  To do this, loosen the screws slightly, insert one end of the spring into the recess and retightening it.  

After you have done the above, reassemble back the printer by placing the upper half onto the lower half.  When you do this, you will notice some resistant caused by the two addtional springs that press against the upper half.  Once you have tightened the bottom screws in place, the two springs will give sufficient pressure for the print head against the roller.  These two pressure points, together with the original spring will produce even pressure across the whole print head mechanism and thus give a very much consistent printing of characters.


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