Three black dots, about 2mm diameter, every 100mm down the length of the paper.

Most petri dishes are either 90mm or 100mm in diameter (halve this for radius)

yeah it surely does

set both valves rocking at TDC

Hi,
Sounds like something stuck on a roller with a diameter of ~1/2" diameter.
Good luck.

sure, put on the buttonhole foot after putting a button into it and using the screw knob to set the length you want.
Turn stitch length knob and stitch width knobs to zero, (always set them to zero first to avoid wear on the stitch selection mechanisim) then turn the left stitch selector knob to the blue button hole symbol. Now turn middle knob stitch width, to the blue buttonhole symbol. Now turn right knob stitch length to blue 1, sew down the first side of your buttonhole until foot slide in the buttonhole foot reaches end stop. raise needle and turn stitch length to blue 2, and sew three bar tacks across buttonhole. Again, raise needle and then turn stitch length to blue 3 and sew back down otherside of buttonhole until you reach the end stop. Needle up, turn length know to blue 4 and sew three bartacks to end. there is a last blue symbol dot on stitch length knob, this will sew a stitch in place to tie off the ends. Raise pressure foot, remove your work and draw top threads to underside with a needle, and tie off or use a dot of fray stop. Done! if you don't have a manual you could email me and I'll send you a copy of mine, tallygirl98 at yahoo dot com.

If you measure the distance of each dots or try to roll the paper and find out that the diameter of each dots are the same. This means that your opc drum is worn out. You can refer to youtube on how to dismantle the cartridge.

You have something on your "**** glass", the narrow piece of glass that the scanner "looks" through during adf use. Get some window cleaner or rubbing alcohol and clean it with a damp cloth. Often, it's correction fluid (Liquid Paper). A little dot is all it takes because the paper is traveling across the dot, effectively drawing a line down the length of the page.

(Please rate this response as I'm trying to obtain the next level.)

Hi Darcy: the "D" stands for Diameter, and the "F" stands for focal length.
so its a 100mm=4 inches. 900mm is how long the light is..to reach the eyepiece.
let me know if this helps.
STH55

inspect the pc drum, if there is no dots, then its ok, also inspect fusing unit rollers and transfer belt for dots and clean laser glass.

This is the add toner light. Replace the tube of toner and will be well.