Oki Microline 491

[Eric1968]

Did you adjust the printhead after you replaced it? The gap between the printhead and the platen roller should be adjusted using a feeler gauge and by adjusting the blue cam. The gap should be 0.35 mm with a variation of 0.02 mm. When the gap is too wide irregular printing can occur.

[krazeekidz3]

Awesome, guys, thanks!! I'll follow up after a visit to the customer's office this afternoon!
Thanks again!!

[blackcat4866]

I don't remember if Oki offers both multi-strike and single-strike ribbons. If you're using single strike-ribbons you can unwind a bit of the ribbon and see if any of the characters are overlapped or printed off the edge of the ribbon. It's harder to tell with multi-strike ribbons, but if it's printing off the edge that edge will become frayed.

Like wazza suggests, check that your ribbon is advancing consistently, and if it lifts that the lift height is correct. It could be as simple as the ribbon not latching in correctly or the drive not coupling correctly (very common with Nu-Kote ribbons).

Who would have thought I'd remember that? I spent a lot of time with Brother, IBM, and Juki typewriters back in the day. =^..^=

[JustManuals]

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Paul@justmanuals.com

I'm thinking you have a ribbon drive problem. If brand new ribbons are being installed, yet the front page varies in ink density, the ribbon is not moving at a consistant speed past the printhead, and an area which has been already hit by the printhead is being used again, or too much in one particular spot on the ribbon, therefor giving a lighter density. As soon as the ribbon actually moves forward, the ribbon is again new and will print darker.
With the power off, you should be able to slide the printhead unit back & forth while watching the ribbon winding mechanism. It should move at the same speed, without any lagging.
The back page will look great because the printhead has printed that through the first page. The first page is the one with the actual ink on it.

Also make sure the platen roller is clean.

My experience on these is limited to working on them over 10 years ago, but I did see this same symptom on the Oki's I worked on back then.

[krazeekidz3]

This machine is printing on NCR paper. The second page looks terrific. The first page is light in some areas, dark in other areas. No particular pattern. The customer changed the ribbon cartridge with several, brand new in the box, OEM, ribbons. (I witnessed this myself!!) No difference! Replaced the print head. No difference. Called me. I have no idea!! Can it be a driver problem? Can it be a power problem? Not sure where to turn. ANY feed back would be greatly appreciated!!
Thanks!!!