Saturday, December 20, 2014

Futile hunt for spring lost inside mechanism of console printer, plus prep to repair FPGA board


My first act was to hunt for the spot where the spring fell off, as that might be a cause of the failure to consistently release the margin rack when carrier return operations start. I discovered it belonged on the pivot that twists the tab torque bar, to keep the link from pulling on the torque bar when it is in its inactive state.

The spring is challenging to fit into place, as it is strong, has the ends bent into an almost complete circle requiring force to push over brackets, the bracket and lever are both thick, and the two holes are deep inside the machinery. I had to use forceps, spring hooks and other devices to try to attach it.

Boom - the spring snapped out of the forceps and flew to an unknown location. I wasn't even sure whether it stayed inside the typewriter or flew elsewhere in the garage. After a sanity break, I continued my search and discovered it deep inside.

However, retrieving it was not the piece of cake I expected (you would think I would know better and harbor deep pessimism, but no . . . ) and it lodged somewhere down inside the mechanism. I spent somewhere between three and four hours (yes, hours) patiently looking, probing and testing but as of mid afternoon I still don't have the spring.

For a diversion, I watched the carrier return mechanism, focusing specially on where the mechanism tilts the escapement torque bar and pulls the link that releases the margin rack to the right. The issue is that a part of the latch assembly is not restoring all the way to its rest position, most likely due to sludge but we shall see what actually causes this.

At some points the carrier return latch is not releasing so the cycle starts over and over - the errant spring is likely somewhere in the path of the clutch latch or release, but it could be a random coincidental new malfunction.

It is maddening to feel that, if I can only find and install that lost spring, I will be able to quickly finish the tweaks and put this printer back together. Depressing to think that I have two different peripherals suffering from a lost item in the mechanism, devilishly hard to locate, without which I can't put them back under power or finish their restorations.


My parts had not yet come and I can't do any testing until I repair the micro USB connector on the fpga board. I think I get everything on Monday at which point I can do the repair and start some testing.

Tonight, to my surprise, the micro USB connectors arrived and I put together the plate which I will use to hold the part in place while I solder it down. I intend to use the QuikChip solder, a special formula which liquifies at a very low temperature. By using my hot air rework gun to heat the connector with its paste underneath, I should get that new solder flowing without the rest of the parts on the board loosening. Tomorrow is the day I give it a try.

FPGA board with missing USB connector right edge mid height

Spare micro-USB SMT connectors

Jig to hold down part during soldering

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