C550 varying punch position

[mascan42]

I have a customer that has a C550 with an FS-518 and PK-512 punch unit. The punch keeps varying the distance from the edge of the page. If I run 10 punched copies, 3 will have the holes closer to the edge than the rest, and 1 will have the holes actually touching the edge. The punch was originally completely missing the page, and causing jams, until I adjusted the punch loop. But once I got the holes back on the page, increasing the loop any more didn't do any good.

Any ideas what might cause this?

[emujo]

The 1st thing I would do is to pull the cover off of the punch PWB and manually dial in the pots that represent the sensors..turn each one by one until they go out, then back till they re-light. (assuming the sensors are clean). Next I would run the punch edge detect in service mode. This should resolve any issues not caused by a bad punch board, or punch sensor. Emujo

[jeroen2005]

Check the mylars in the conveyance unit .These are seated before paper enters the punch unit,if they are damaged this may cause a timing problem.

jeroen2005

[mascan42]

The newer finishers (on the C550) don't have any pots on the board. I've already made the edge detect adjustment, and checked for any damaged mylars. There's been no change.

Just to be clear, it appears the paper isn't being delayed by slipping rolls or obstructions in the paper path, but the opposite - the punch unit is firing too late.