Sunday, March 27, 2016

Converting 1442 adapter for both mirror and virtual mode, plus plotter restoration start

More distracting tasks to keep me away from the 1130 project. My daughter's car is leaking oil around the valve covers, which causes smoking oil entering the ventilation system to the detriment of the riders. I bought new gaskets and parts and did the repair myself.

A gasket on the cam chain tensioner is also a source of leaks, so I replaced that. This involved partially disassembling one of the camshafts to get access for the replacement. Two special tools, easily found on ebay, were required.


Implementing mirror 1442 reader/punch

I began coding that additional logic in the fpga first, so that I can first verify that it 'does no harm' to the existing virtual 1442 functionality. I was surprised by how lightweight the change is. Only three functions force data onto the 1130 bus - XIO Read, XIO Sense ILSW and XIO Sense Device. I used my mirror versions of these, which capture the data that is written by the real, functioning adapter electronics inside the 1131 instead of driving data onto the bus as the virtual driver must do.

Next, I have to skip over the steps in the main process which trigger the 80 emitter interrupts on IL0, since the real adapter electronics will do this. I also have to skip over the step that triggers the completion interrupt on IL4, for the same reason. One signal, which indicates whether we are in mirror or virtual mode, will direct the main FSM to take or skip these steps as appropriate.

The remaining change is in the pre-read buffer logic, which now has to capture the data written by the real adapter electronics (via my XIO Mirror Read module) and store it into the buffer. This is driven by a new mirror read process that triggers a buffer write at the end of an XIO Read.

The last little bit was the special transaction from the PC that will set or unset the mirror mode signal. I chose the Write Device Status transaction (command code 6) and the low order bit will switch the adapter to mirror mode if set, otherwise it will flip the adapter to virtual mode.


I picked up the plotter, which does appear to be complete as far as parts, with the only visible damage being the dented and bent main drum upon which the paper is carried under the pen. The tasks ahead are:
  1. Repair the drum,  returning it to a constant radius cylindrical shape
  2. Get accurate pictures and colors for the control and side panels of a 1627
  3. Repaint side panel to IBM color (IBM gray)
  4. Repaint control panels to IBM color (black)
  5. Create and attach white labels on control panels
  6. Remove Calcomp label on front bar
  7. Create and attach IBM 1627 label  and "made in america" placard to front bar
  8. Reassemble plotter
  9. Attach plotter to slave fpga board
  10. Test and adjust plotter
As far as task 2, I collected quite a few pictures that show me the colors and labeling with enough fidelity that I can paint the plotter properly and fabricate realistic labeling. I have powder coating colors corresponding to both gray and black as used by IBM in the 1130 generation. I will just need to sandblast the panels to be painted and then find a powder coating facility I can use.

Task 1 - drum repair - is going to be the most complicated part of the project. The drum has a big dent and that has also bowed the cylinder out of 'round' in a couple of places. It is an aluminum drum, this inherently soft and ductile, which might allow me to get it close enough to true. If I can, then I can spin it with an abrasive to even out very slight variations.

Another possibility is to make a form out of wood or plastic that matches the desired internal volume of the drum, allowing me to force the aluminum down over the form to true it up. I am skeptical about this method but it is worth considering. As well, I need to think of other repair methods.

Another possibility is to find a substitute aluminum hollow cylinder whose ID and OD match this one. Cutting it to length will be relatively easy and then I can simply replace the dented drum with a new equivalent. The key, of course, is to find a readily available drum with the magic combination of inner and outer diameters plus sufficient length.

I disassembled the drum to find it is a light easily bent surface that had sound deadening foam on the inside. The cylinder has small pop-riveted tips that will fit the perforated holes in any paper inserted into the plotter. These would be quite hard to move to a replacement drum surface.

Dented drum

out of round condition

Internal supports and sound deadening foam

Pins riveted into drum surface

Inside view of pop riveted pins


  1. Not relevant but I was afraid your gartner email is no longer valid? Anyway: you will enjoy watching this talk by an 18yo collector buys a z890...

  2. I retired in early March - email no longer active. You can read me at carl dot claunch at sbcglobal dot net