Sunday, March 8, 2015

Major progress on solenoid for print column 60 of 1132 printer


After I published the last post, I went back into the garage and made major progress towards restoring column 60 printing. I took the magnet assembly off of the magnet unit (yes, IBM named them this way). That had its moments, with several frozen bolts, apparently tightened by a gorilla. A couple required high impulse to free, delivered with a off-center chisel and hammer, but they came out.
Magnet assembly after removal from magnet unit
The other half of the magnet unit, the levers that convert armature pivot to release of cam clutch
The assembly came off and allowed me access to three screws underneath and two on the ends that hold the top bar of 24 magnets onto the assembly. With it removed, I could move to the workbench to take advantage of the greatly improved access to the coil.

Magnet bar (not official name) containing 24 solenoid coils
What I thought of as wedges were instead dents created in the core to hold the coil on firmly. Using tiny screwdrivers on each side of the core, I bent the plastic bobbin away from the dented core and used a hook tool to pull up on the core. I was able to edge it up and off the core.

Coil removed from core - notice dents on sides to wedge the plastic bobbin in firmly
The coil was still an open circuit even with all possible manipulation of the leads. I then began removing the fabric covering to see the condition of the coil connections between magnet wire and the leads. It was a slow careful process to nip and unwind a few strands at a time to ensure I didn't cut the magnet wire leads coming out of the winding.

The bad solenoid for printing on column 60, an open circuit
Once there was full access to the two connections, the leads and their magnet wire end, I tested the continuity from the solder points of the connections. We have an intact coil - perfect 143 ohm resistance measured and no cut-out regardless of movement of the connections.

Magnet wire connection points have continuity - "Houston, we are go for liftoff"
All I need to do in order to fix this is to tack solder new leads to the existing connections and then carefully rewrap insulation around the coil. When that is done, it can go back on the core, the bar can go back on the assembly, and so forth until the printer is completely reassembled.

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