asked Sep 6, 2007 at 8:36pm
Unknown Printer

Oki Microline 320 Turbo 9-Pin Dot Matrix Printer

I have one of these that I need to figure out what's wrong with it. I'm not exactly fimiliar with these dot matrix printers.

The user attempts to print labels, it prints about 6 of them and then they get these strange characters. They turn the machine off, then on again and it prints another 6 labels, then does the same thing again. The print head has been replaced. Is this a board problem? What can I do to fix this?

Make sure there isn't a computer issue.

Make sure you have a good printer-computer cable and that its solidly connected on both ends.

Run the printer self test by pressing the LF button while turning on the power.

If printing problems are still evident during the self test and/or through the I/O, remove the case if you haven't already and direct some cool air at the main board. (There are several latches just under the front edge of the case that can be released with a slot style screwdriver.) If extra cooling extends the print time or solves the problem, I would replace the main board. Regardless, the main board is almost certainly the problem. There are no comprehensive schematic diagrams in the service manual to facilitate repairing it. Get the service manual free here.

You can inspect the carriage trailing cable but I've never seen a problem with them unless some strange "mechanical event" has occurred.

Blow the paper dust out, particularly around the paper sensor.

Clean the platen. There are products made for that purpose.

If the backup roller assembly roller is made of plastic, replace it. The plastic ones get a flat spot eventually and cause margin drift.

Lubricate the carriage drive rack gear with a light grease. If you are bold I suggest taking it out and cleaning it.

Clean the carriage rod and lubricate it with a couple of drops of very low viscosity oil. I use Tri-Flow that is available at cycle shops. To much lubrication just helps attract paper dust.

You can get parts at

For your amusement: I once found dog biscuits inside one of these carried there by rodents. They even gnawed the case around the I/O opening. That taught the customer the pitfalls of feeding their customer's dogs.

by Bert on Sep 7, 2007 at 12:00am Add comment
I have worked on a lot of these.
Bert's advice on maintenance is spot on.

It sounds like it is either a computer problem or the emulation on the printer is set wrong.
i.e Printer set to Epson, the Computer is sending IBM control codes.

Find a user manual and put the printer in hex dump mode and you will be able to see what codes are being sent to the printer.
by mcprinter on Sep 7, 2007 at 12:49pm Add comment
It appears that two techs are better than one. mcprinter is trying to give me a head ache by mentioning hex codes. Seriously, the input is appreciated. I didn't think of an emulation problem. Refer to page E11 in the Users Guide to determine which mode the printer is in.
by Bert on Sep 7, 2007 at 5:47pm Add comment
Guess I will have to check the emulation out. I took the printer apart and took the boards out. I was going to swap out the boards with a brand new one we have but of course the boards are a different size. Nothing is simple these days. Hope I can get it to print more than 6 labels without the strange characters.
by bjb1178 on Sep 7, 2007 at 6:16pm Add comment
I have this printer and we use it to print 4 part forms. Just now having problem with the print not going all the way through to the 4th copy? Is there an adjustment that would fix this?
by unknown on Dec 17, 2013 at 8:44am Add comment
htassels...most Oki's have a lever that adjusts the pressure exerted by the printhead. Move the lever to a lower number, and test. You may have to go through this process a number of times until you reach the ideal pressure, enough to print through the forms, and not so much that the paper or ribbon bind. Hope this helps.
by unknown on Dec 18, 2013 at 6:12pm Add comment
while printing an invoice it sounded like it jammed and stopped printing. I have inspected, looks fine, red alarm light comes on, printer head jolts and buttons work when alarm light on. shut off, restart and same thing - alarm light, printer head jolt and!!!
by unknown on Jan 28, 2014 at 4:25pm Add comment
bundy...You should be getting a series of solid and\\or blinking lights on the control panel. Let us know what is blinking and staying solid when the error occurs. Hope this helps.
by unknown on Jan 28, 2014 at 5:17pm Add comment