Sunday, August 14, 2016

Beginning restoration of light panel on 1131


I inspected the front panel and the loose honeycomb to decide how critical is the spacing for gluing it back into place. I also wanted a clue to the adhesive which is now failing in my machine (and that of a friend whose panel has every honeycomb loose. The solution I develop will work for both machines.

I didn't have an adhesive at hand that seemed ideal, so I decided to take the honeycomb over to Tap Plastic tomorrow to find something useful. Once I have the glue, it will be short work to add the loose honeycomb to the others.

I will still have the gap between the honeycomb vertical sides and the vertical plastic holders which keep the panel in place. I am not sure if I will glue that or not, it will depend on how quickly the glue sets, how much contact pressure it needs and whether I can position it accurately once glue is applied.

The next problem I faced was the lamp contacts themselves, or more directly the corrosion on lamp leads, lamp sockets and circuit card pins. I have some lamps which registered as open circuits when measured at the pin holes on the socket but if I make contact with the lamp wires themselves, the bulb is fine. It is corrosion on pin hole and wire that blocks a good contact.

lamp wires in pin holes, oxide on both inhibiting connections
I need some solution to remove the decades of oxide without harming any of the parts. The approach I have heard of that has promise is to use two baths in a row for each part. The first bath is a salt and vinegar solution, which will dissolve the oxide layer. The second bath is a sodium bicarbonate and water solution, which neutralizes the acid when it has done its work.

Finally, I need a way to repair and replace the bulbs in the pedestal. The bulb fits in the socket with friction holding the lead in contact with the pin hole and the pin from the PCB. The pins on the PCB, one fixed on the SCR and the other more flexible, are pushed into the pin holds of the lamp socket to make contact.
PCB with SCR and flexible pins that fit into lamp sockets
Unfortunately, there is another mating operation. The lamp sockets are pushed into the honeycomb to form a friction fit. The challenge in repairing the light pedestal is to pick the right order for the matings and figure out the mechanics of getting each PCB worth of lamps installed; the sequence of PCBs installed is a third variable in this process.

Lamp sockets press-fit into honeycomb
I did determine that the various PCBs (rows of lamps) will pivot out of the way, thus potentially I could install each row in sequence, perhaps from lowest to highest, having improved access for all but the top row.

I believe I will have the lamp sockets pressed onto the PCB pins, swing the PCB into position and use small tools to help guide and push each lamp socket into the honeycomb. This presumes I have no more brittle wires between lamp and socket, as these were breaking off whenever I disturbed them before.

The light panel must be repaired or at least set up to avoid shorts before I can safely apply power to the 1130 system and do any other work with it. My preference is a permanent fix for the panel, so that will be plan A for the next few days.

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