From: joe@user.com   
      
   "Rick"  wrote in message news:45060021.5F2D6F60@rcn.com...   
      
   > This all begs the question: Does anyone know what this problem is with   
   > dot matrix printers as they age?   
   >   
   > I've seen if more than once on a well used printer where the head   
   > transport seems to just "jam" or stick, usually when traveling in a fast   
   > motion, creating all manner of illegible chaos when it recovers from   
   > getting hung up. I've had the problem with a Star Micronics NX-1000 and   
   > and old Epson that predated that one.   
   >   
   > On most of them disassembling the printer to see what type of bearings   
   > are moving across that carriage rail is very difficult. But it seems   
   > hard to believe the head transport is running on bearings that use no   
   > lubricant at all when shipped.   
   >   
   > Rick   
      
   I've seen a couple of problems with old printers.   
      
   One is 'indexing'.  In some printers, there's a 'strip' that has slots or   
   bars   
   on it.  This is used to index where the head carriage is.  I've seen these   
   get dirty and now the head position gets confused at certain spots.  I've   
   had some luck using a 'gun patch' LIGHTLY doused with alcohol wiped   
   over the strip.  Also examine the sensor that reads the strip and use a   
   small hobby/model paintbrush to brush away any foreign matter.   
      
   There are some printers that don't use the strip, and encoding can be in   
   a 'wheel' assembly that the cable turns.  I'm not sure, but my personal   
   perception is the 'ink jet' printers I've seen to lean towards a plastic   
   strip that is sensed by the head.  One I looked at seem to have position   
   information encoded into the strip and not just be 'bars' that are counted   
   by a quadrature detector.   
      
   I'm not too comfortable about running ANYTHING, even a dry patch,   
   over one of these encoded strips.  However, if it's not working, I suppose   
   I'd have nothing more to lose.   
      
   The other problem can be friction of the head carriage assembly.  In some   
   cases, the motors are 'steppers' and the software assumes that a 'step   
   sequence' generates a known degree of movement.  In these cases, the   
   carriage 'registers' it's position, usually at the left, and as it moves out   
   or   
   back, it should know where it is.  The problem occurs when the printer   
   comes back to 'home' (or to the other side) and it an 'end of travel' sensor   
   is detected (or not detected) at the correct position.   
      
   USUALLY, this is because the carriage has 'missed' a move, and that   
   can be because of 'friction' on the rails or it can be because the motor   
   has gotten weak with time.  If the motor has shorted out a winding, it   
   may still appear to work, but one of the 'steps' may not have as much   
   torque as before, causing the carriage movement to fail occasionally.   
   This kind of failure can occur more on starts or reversals than on constant   
   movement.  If you see printouts where the vertical alignment 'drifts',   
   that's usually a sign of motor (or it could be lower voltage issues)   
   problems   
   and not necessarily friction.  However, SOMETIMES, it can be corrected   
   by reducing friction.  But then you're just hiding the problem for another   
   day.   
      
   Bottom line is there's not a simple consensus as to how these things work   
   and how they fail, other than some of the obvious issues and how they   
   COULD interact with the firmware in the printer.  It really depends on   
   the firmware in what it expects to find and how it deals with things when   
   what it finds isn't what it expected.   
      
   Mike   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)