Tuesday, June 21, 2016

Breakdown, a broken banjo bolt, and glue everywhere.

My SD300 broke down at the end of 2015, its first serious fault.  The machine had clocked over 6000 hours of build time, plus an additional 10,000 hours of power-on time, so maybe it was just about time something broke.

I had to mail-order various replacement parts from overseas, so I did the work in short sessions over the course of several months.  The machine is running now.

It started when I had left the SD300 running unattended, which wasn't uncommon.  I came home to discover the machine halted with a severe fault, a broken-out panel underneath, and a puddle of solvent-glue.


No doubt there was a glue leak somewhere inside, so I removed the exterior cowl to trace it back to its source.

Opening left side cowling to reveal cable carriers, wiring harnesses, and power driver circuits.

Solvent-glue had leaked onto the cowling panel and melted through the bottom.
There was melty plastic residue all over the cable carrier for the iron bridge.

Rolling back the cable carrier revealed even more plastic residue.

A vinyl wiring harness had disintegrated where it crossed under the steel-armored tubing at the end of the cable carrier.

The solvent deposited plastic reside everywhere it leaked throughout the SD300.

The source of the leak was a tiny, hollow banjo bolt that had broken in two.

Evidently the leak originated at a hydraulic connection, referred to as a banjo fitting, where a steel-armored PTFE tube was attached to a manifold by way of a hollow bolt that had been broken in two. This is a common type of connection in hydraulic equipment, but the SD300 employs an uncommonly small size: that's a tiny 5 mm screw thread!  It was really tough to find a matching replacement in North America, but I eventually managed to source a replacement through Airlines Pneumatics in the UK.

But the SD300 needed more than just replacing the broken bolt because the solvent glue had traveled along the armor of the PTFE tubing by capillary action and destroyed a vinyl wiring harness that had been routed through the same cable carrier.  The damaged harnesses and fittings needed to be replaced, too.

That's enough about the damage.  The machine is repaired, but I'll post pictures of my repair work separately.

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