OKI dot matrix printer: annoying problem... - Page 1
Forum section: electronics / general

author: iamwhoiam
author_rank: Contributor
timestamp: May 24, 2012, 12:06:03 am
content: I have an OKI Microline 83A dot matrix printer, made in 1983. It is fully working, but has a weird situation whereby when I plug in the parallel (centronics) cable between it and my PC, halfway through booting (when PC is on, basically) there is a slight buzzing and then the resettable thermal trip (on mains inlet PCB) will trip out. All the jumpers and DIP switches are set correctly, it seems to be the parallel link to the PC which causes the thermal trip to trip out, nothing else.Any ideas would be gratefully accepted - this is fiddly tech!Thank you all :-)

author: siliconmix
author_rank: Frequent Contributor
timestamp: May 24, 2012, 12:22:36 am
content: maybe it's time to upgrade.use the motors in there for something.if you've got a lathe the carriage bar is excellent for setting up a lathe up they're made to close tolerances.oh yeah and you get a plug

author: PbFoot
author_rank: Contributor
timestamp: May 24, 2012, 01:13:48 am
content: Well, it's hard to say without probing the guts of the printer, but I suspect that something in the printer, probably a motor, is drawing way too much current.It could be that when the parallel port comes online, the printer may execute a "home" routine that moves the printhead to the home position or something. When the motors involved have current applied, and the motor is shorted due to an internal failure then the power supply in the printer trips. It might be hard to get parts for that thing though.Another long shot could be that the parallel cable is bad, and its shield is shorting multiple data lines. I doubt that though.-PbFoot

author: senso
author_rank: Frequent Contributor
timestamp: May 24, 2012, 01:45:10 am
content: Bad grounding in either the pc or printer side?Like current flowing in the centroncis cable(lots of current)

author: G7PSK
author_rank: Super Contributor
timestamp: May 24, 2012, 08:07:57 am
content: When I had an Apricot computer and an OKI dot matrix printer the printer had to be plugged in before starting the computer. The other thing with those dot printers is the pins will seize up in the head. I used to dissemble the machine and clean it with pure alcohol.

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 24, 2012, 08:13:56 am
content: There is a +5V output in the Centronics spec on pin 18, not sure if your printer has it. It should be current limited anyway, and it should not run to the PC, and the PC should not do anything with it, but who knows...? There is also a reset on pin 31, which is likely to be activated on powering up your PC. You're free to cut both lines in the printer end of the connector to see if it makes any difference.Also, I think it's a bad idea to connect the cable while your PC is booting. Yes, there are switches which can switch from one printer to another, but they don't switch all the lines. Also, the pins in these connectors like to bend and short stuff and give you all kind of strange effects. Then, it was already mentioned, make sure that both the printer and the PC are on a grounded outlet.In the end, what you see should not happen but since it does...

author: amyk
author_rank: Super Contributor
timestamp: May 24, 2012, 10:02:19 am
content: Definitely make sure the outlets are grounded and wired correctly. It could be a potentially dangerous situation.

author: ErikTheNorwegian
author_rank: Frequent Contributor
timestamp: May 24, 2012, 09:33:25 pm
content: If You need a new printer like that i got a brand new Oki Matrix Microline ML280 printer in storage, never used..You pay shipping, printer for free..