Oki 590/1 -- Ribbon Drive

An Oki 591 is in the shop with an inoperative ribbon drive. The wire projection at the top of the drive spindle is sheared away. Apart from that, the mechanism is working fine. Here's a view of the ruined spindle.

A replacement ribbon drive gear case is P/N 51228501. We don't have one in stock, and the customer would likely squawk about the price anyway, so I'll try replacing just the spindle with one from a salvaged gear case.

The ribbon drive gear case on a 590/1 incorporates an auto gap-setting mechanism. This one appears to be working ok, so this should work out alright.

The gear case has four claws holding it to the carriage. Unlike the 320/1 Turbo, this gear case is not entangled with the carriage cable, so it's quite easy to remove it in one piece with the carriage in place in the printer.

Carefully separate the two halves of the gear case, and you get to here.

The ribbon drive spindle should be the only item to remain with the upper half.

With none of the gears askew or in disarray, it's a straightforward job to replace the ribbon drive spindle and snap the gear case back together.

You have to check printhead gap and parallelism on reassembly. The manual calls for a 0.014" gap at gap setting '2'. That seems too small a gap to me; I set these printers to 0.016" at gap setting '2'. To manually obtain a desired gap setting, turn the adjustment screw gently as you move the carriage -- that gets the big auto-gap wheel to jump an increment. Repeat as needed to get to position '2'. With the correct position selected, the gap and parallelism adjustment procedure is no different from that for the 320/1 Turbo.

Anyway, this repair went nicely. Fortunately, the machine overall is in good shape, and all it needed was the ribbon drive spindle and some cleaning up. More often than not, these things are basket cases when they arrive here -- in need of a thorough overhaul, or the short journey to the big bin out back.

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