How to refurbish plotter pens? (roller-ball pens)

A late follow up on this topic. I got my IBM 1627 running. Actually it is not mine, it belong to my father that got it used for his home built computer somewhere around 1977. It became a project that never was finished... There are still some simple drawings he did on how to interface it. http://i.imgur.com/8JK8wwO.jpg http://i.imgur.com/8YJA0Qb.jpg First thing I recognized was that the Mallory FP type capacitors in this one both measured below 1nF capacitance. A quite serious problem. It turned out that when I pulled them apart the positive electrode was subject to severe corrosion. It was simply cut off.. http://i.imgur.com/XUaQtPn.jpg http://i.imgur.com/nMLoFbN.jpg One of the stud mount 1N2547 rectifiers diodes was broken at off from its studmount in the middle of the insulating ceramic material. Since this type of rectifier was hard to find I replaced it with a modern part. Then on I replaced other electrolytics that all measured marginal (after all this machine is from 1967, 50 years old!). The two Mallory AC capacitors which are the run capacitors for the paper feed system were replaced as well. Not that they measure bad but I simply don't like oil filled caps from the sixties. They might contain PCB oil. And I didn't find a list that certified that Mallory RP-3301 is PCB free. Then the PSU was fine and all voltages measured well. On to the mechanics. The drum was working fine in both directions, but the carriage was not moving in either direction. Checking the electronics revealed that it tried to drive the stepper motor but nothing happened. It was stuck. The motor was removed and disassembled. There was a small gearbox on top of the stepper motor and it turned out that the motor axis was completely stuck. http://i.imgur.com/O043J9J.jpg By removing the last six screws it was possible to get the axis out by knocking on the axis with a screwdriver handle. It turned out that there was quite some rust in there. Cleaning, re-lubricating and new grease and it worked quite well. One note for others who repair these. Do not remove the big wheel that is driven by the stepper motor and drives the carriage. It is not necessary unless you plan to put some new grease in the gearbox. It is a small hell to get the carriage cable back into position again.. After this the plotter moved nicely in all directions and then it was time for serious testing with pens which bring us back to the topic of the thread. This plotter was supplied with non-pressurized pens. As far as I understand there are pen holders for both varieties of pens as well as felt pens. Mine are definitely non-pressurized. http://i.imgur.com/ZquhQMT.jpg As per Randys suggestion I put them into an ultrasonic cleaner and they become much cleaner. Then onto filling them which turned out to be a complex and a messy business.. From what I understand there are different types of ink. The type of ink that are used for reservoir pens or Harry Potter feathers which is more liquid and then a thicker ink which is used in ballpoint pens. The former is sold in small bottles the latter is not sold except for in ballpoint refills. The next step is to try to extract ink from the ballpoint refill and use a ink refill syringe to push it into one of the cleaned pens. We'll see how that works out.

The other option is to find new pens with the same diameter which can be cut into the correct length and tip dimensions. Maybe even plastic ones will work if they are stiff enough. In parallell I am working on the interfacing part. As far as the description in the manual interfacing is quite simple. Either negative going or positive going pulses, at least 10V amplitude and more the 4us long with less than 10us rise time. Source impedance less than 500 ohms. A ULN2004 or similar together with some simple AVR microcontroller will probably do it. /Mattis