Saturday, May 23, 2015

Began reassembly of 1052 console printer mechanism, plus failed attempts to tack the jumper wire on the fpga board chip lead


I began reassembling the operational selection magnet assembly, which I know has some very very difficult reassembly steps due to almost nonexistent service clearances. However, I am currently stuck on what should be a simple task.

One screw has to hold down a bracket on the side, but the straight line path that a screwdriver would take is blocked by two screwheads jutting out from another assembly. They are too close to find a very short screwdriver, perhaps 1.5" from the screw I have to turn, but close enough to make any screwdriver have to fit at an angle.

That makes rotating it to start into the hole threads a very difficult problem. It is inside where I can just about hold the screw with two finger tips, or with a forceps, but can't rotate it without putting sideways torque and skewing it so it won't enter the threads.

I spent an hour in a near infinite cycle of positioning, turning, skewing and eventually dropping the screw. Finding and picking it up begins the next cycle. This isn't the 'hard' part of the reassembly. which involves attaching five clevis hooks onto rotary arms up inside the inaccessible bowels of the mechanism. These clevis fit onto the actuator rods of the five magnets in the assembly I am installing.

To install a clevis, which can rotate around the rod on which it is fastened, you need to pry one of the two arms away from the other. One arm has a cylindrical pin that fits inside a hole in the actuator arm up inside the machine. The other arm holds the pin inside the hole; it has to be pried apart to allow the pin to slide over the actuator arm edge and find its hold in the center.

Thus, one hand to hold the arm with the pin. One hand to hold the other arm and pry it apart. One hand to stop the clevis from rotating, twisting the arms away from alignment. One hand to hold the clevis over the actuator arm and push it down to get the pin into the hole. That is four hands in a space that is deep inside a mechanism with perhaps 3/16" clearance on the sides, too small for even a small finger to enter.

I had no need to worry about connecting those clevis rods, since I had yet to get the screw into its hole which is one step earlier in the sequence. Fortunately (?), I was finally able to get the screw started and begin connecting clevis rods. The first two were rather easily snapped onto the arms.

After a break, I went back to work on the remaining three clevis connections. Within an hour I had them all attached properly. I have a few more parts to install and then a couple of adjustments that must be made. A pivot arm trips a microswitch to indicate the period during which the 'long' actions are in motion - those are tab movement and carrier return, which take a variable length of time depending up on how far the carrier must move to reach its target, either a set tab or the left margin.

The pivot screw is held by a lockwasher and nut that are inserted inside a bracket where fingers can't reach. I have to figure out a way to hold the nut and lockwasher in position so that I can place the pivot arm on the other side of a bracket and then thread the pivot screw in place. It will be tedious but not otherwise complicated.

The magnet assembly I just attached is adjusted to put the armatures just below the actuating arms they serve and to ensure that the armature end of the clevis rod is a bit forward compared to the actuating arm end. Not particularly finicky adjustments, easy to spot and then I tighten three mounting screws and one mounting nut.

With the assembly adjusted, a spring is attached from one of the mounting screws to the pivot arm. I can check the pivot arms and microswitches to be sure they are closing appropriately when the mechanism is actuated and opening when it relatches.

Microswitches for the shift mechanism then have to be remounted. I needed the bracket they are on swung out of the way while I worked on the magnet assembly. They may need adjustment too.

I closed up the shop before installing the pivot arm and screw, after the pivot screw fell somewhere I couldn't readily find. At least I had a method for holding the washer and nut in place . . . if I only had the screw at the same time.


Gave another try with all the magnifying and lighting tools I have, but I just can't see well enough to position the wire, know it is touching the right lead, and then to apply the solder to tack it down. Based on a suggestion from a blog reader, I bought a USB microscope, to try to lower the cost of the tools I will need to buy. It will arrive late tonight.

The microscope has limits on its field of view and focus distance, but otherwise should give me an accurate enough image. I may not be able to work while the microscope is in position, due to tight spacing under the unit, but if I can position the wire in place and hold it there with decent accuracy, then I can solder with the lesser magnification of my other tools (I think).

Tonight, when the microscope arrived, it was too dark and late to work on the board but I could experiment with the microscope itself. It seems to work great - should be just what I need, even with the shroud in place. Tomorrow I will put it over the board and determine how helpful it might be. There is a chance I will have to remove the plastic shroud that protects the LED light ring and camera lens. 

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