OKI laser duplex unit doesn’t work

OKI C5650 or C5750

This was a weird one. For some reason my OKI c5750 printer (similar to c5650) started ignoring its duplex unit. Stuff was printing on two sheets, single sided. I checked the Windows drivers, and that Duplex long-edge was enabled on them and on the printer control panel. But nothing was doing. The two single-sided sheets came out instead of double-sided, and what’s more it seemed slower than usual.

I initially thought it was a Windows fault introduced by my recent troubles. Had I restored the printer driver to a weird state? But after half an hour of fishing around I finally found the problem on the web interface. It’s subtle.

You can select the weight and type of paper for various trays. It turned out that the tray I was using was set to “thick” and “glossy”. I reset this to “normal weight” and “normal”, and everything started working again. I assume that the OKI internal software won’t send think paper (i.e. light card) into the duplexer, but it doesn’t tell you this. The Windows restore must have set the manual feed tray to light card. This would also explain the slower roller feed.

I hope this helps if you’re also having trouble.