Monday, August 15, 2016

Restoring light display panel, gluing and oxidation removal


I picked up the vinegar, sodium bicarbonate and salt to proceed on my deoxidation treatment of the light panel parts. In the afternoon I made a batch of each solution - vinegar/salt and bicarb - then tested on a few lights and holders.

lamps and holders soaking in salt and vinegar solution to remove corrosion
The first batch of eleven lamps worked great after the chemical dip - all of them had reliable low resistance. I put a next group of 16 lamps through the wash and discovered two of them with unacceptable high resistance after treatment.

Sodium Bicarbonate solution to neutralize acid from first dip
They were not open, but measured in the multi-kilohm range instead of the near zero resistance that a good bulb should display. Since one had the brown residue inside that is typical of a blown lamp, I took this as an indicator I should swap out the bulbs.

I have more than 100 bulbs still to pass through the baths. Removing them from the SCR board pins is a time consuming and careful process, which means I will likely spend much of today working through all the light holders, deoxidizing them and readying them for reinsertion.

Once they are all clean and any failed bulbs replaced, I have to carefully insert them on the SCR board pins. The assembly sequence for the light pedestal requires all bulb holders attached to the boards, before I swing each board into place and carefully work every lamp holder into the honeycomb cell where it belongs. Reinserting lamps will be a task for tomorrow, while the front panel is glued and sets in place on the front of the display.

Quite a few bulb holders are wedged onto the SCR board pins by the corrosion affecting both. It takes some serious work to get each such bulb loose. I lost a few bulbs which broke off at the glass envelope, but most are working out okay. Just to be safe, I ordered 48 bulbs which are electrically identical but physically smaller, which will serve in a pinch as a substitute in the bulb holder.
Replacement mini bulb at top, same light emission and electrical characteristics as bottom bulb
Surface of honeycomb that bonds with horizontal plastic bar
Side of honeycomb which bonds with vertical plastic bars inside metal case
Side of honeycomb which bonds with adjacent honeycomb segment
After visiting Tap Plastics for advice, I bought some PS 6 fast set acrylic glue to rebond the plastic honeycomb. I wasn't sure whether I needed to sand off the old adhesive first, but decided I would do that to give a flatter surface and better opportunity for bonding.
Fast set acrylic glue to repair front light panel
After sanding, I tried a dab on each of the two plastic types to see how it worked, before trying to glue the honeycomb back in place. Everything looked good, so I glued up the loose honeycomb to the front panel assembly.
Repaired front panel with honeycomb segment glued back into place
The glue specifies a wait of 24 hours to reach maximum strength, so I will wait until tomorrow to glue the entire panel back in place against the two vertical plastic bars that should hold it firm in the metal box.

I am also thinking of aids I can use to make the final assembly job easier. One of the problems is having six layers of PCBs on each side which need to be swung out of the way, so that only one at a time is being manipulated into position. I think I can make use of rubber bands to hold all the others out of play until needed. I have to find a good set of anchor points for the far end of each rubber band.

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