Sunday, May 24, 2015

Reassembled 1052 console, working on carrier return issue, while fpga board in interface box is still fubar


This morning I found the pivot screw and invested a half hour trying to get the nut and lockwasher in place to be threaded into by the pivot screw. I have some masking tape holding the lockwasher in front of the nut, with the hole opened up for the pivot screw thread.

Putting the nut/washer assembly on my smaller forceps, I tried to hold it in position to start the thread from the pivot screw, but several projections on the bracket and nearby mechanisms block me from having a direct vertical approach with the forceps. Attempts to compensate by cocking the nut in the forceps teeth didn't work.

I then hit upon the idea of using some soldering tools I had which were spring clips that could hold the nut and lockwasher at their edge, leaving the hole free. With a bit of effort, I was able to get the pivot screw to mesh and tighten. It was easy to finish up, putting back the springs and the shift magnet assembly to finish up this task.

Now, I have to check and adjust the varous mechanisms to get this to tab, space, backspace, return, index and of course type properly. First up, I had to unlock the various latches that were set while I worked on the typewriter. The original problem that caused me to remove the magnet assembly was failure of the carrier return mechanism to unlatch - which I suspected was due to a missing spring being somehow wedged inside interfering with the CR release.

One big zone of impaired visibility was between the magnet assembly and the operational clutches, but I have just eliminated that by the dis-assembly and re-installation I finished today. I now have to look in a number of nooks and crannies that are covered by many other arms, pivots, levers, gears, rods, springs etc.


Using the USB microscope, I could position the wire well enough to tack it down with solder. I had a bit too much solder, creating a bridge between leads 70 and 71 of the USB chip, but I was able to use some wire braid to wick up the excess solder. It appeared that the wire was attached to the proper pin with no shorts to adjacent pins.

I attempted to load the fpga bitstream, an operation that worked before the damage I had caused but alas it still failed with an error that the 'Done' line didn't go high. I suspect this means the lines I have connected to the USB chip are broken on their way to the Xilinx Spartan 6 chip. Since these pins are balls hidden underneath the chip (a BGA surface mount type), I won't be able to access them to tack on a wire.

The flash is not visible to the USB chip, meaning I have more damage than I thought. I am down to one route to possibly load the fpga, otherwise the board is pure junk. I have the JTAG pins accessible on the external connectors, which might allow me to load it from the bit file with an external circuit I build on another board.

I did pick up a inexpensive fpga board, based on the Altera Cyclone II, which seems to have enough IO pins to use as a slave board. It does not have a USB link on it thus it can't be a substitute for my ztex board. At less than $30, it is a good option for supporting major peripherals such as disk or tape drives, linking them to the SAC Interface Box.

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