Monday, July 4, 2022

Work on securing light panel with new mounting hardware

 NEW LIGHT PANEL ATTACHMENT BUILT

The IBM designed light mechanism behind the display panel above the 1053 makes use of a nylon honeycomb (the same was used to hold the display panel lights on the IBM 1401 computer), with bulbs press fit into each cell of the honeycomb. The bulb is inserted into a nylon holder first, with the wire leads threaded through holes in the holder and bent to each side. Pins press into the rear of the holder, making contact with the lamp wire and completing the circuit.

The other ends of the two pins for each light are on small wide boards that support either 8 or 16 lights each. On the board is an SCR with a fixed pin, plus another pin on flexible pigtail wire. The rear of the board has a pin that is connected to signal wires from the 1130 circuitry. On the left or right side of the board are thick power wires that bring the 7.25VAC, ground and lamp test power.

The lights are packed closely together, with just 3/4" between each vertical row of lamps and thus the boards are 3/4" apart. The lights are 3/8" apart left to right on the boards. This gives little clearance to reach in among the six rows of boards and 16 to 32 pins that have to be pressed into the 8 to 16 lamp holders that are fitted in the honeycomb. 

An alternate method is to remove all the lamps, press them on the pins, then try to swing the entire board in place and press all 8 or 16 holders in the honeycomb. Once again, very little clearance exists. 

This is a very frustrating and tedious process that has to be done whenever a light bulb has burned out, in order to replace it. Further, on transport the lamp holders tend to work out of the honeycomb leaving the boards and lamps dangling in a huge mess of about 150 lamps total. 

As one final burden for owners of old 1130 systems, the honeycombs are glued to Lucite blocks on the left and right that were threaded to hold the honeycomb and front panel in place. The glue between the lucite blocks and the nylon honeycomb almost always has failed, leaving the front panel wobbling or fallen out. Sometimes the honeycomb, which is an assembly of smaller blocks of honeycomb, comes apart as well. 

I designed a new method of attaching the lights to the honeycomb and the 1130 circuitry to greatly reduce the burden of replacing bulbs. I created a single large PCB that fits across the back of the entire honeycomb, supporting all of the lamps on one board. This has surface mount SCRs, connectors and other parts installed to completely replace the small wide boards and nylon holders used by IBM. 

Up until now, I had this board, with all the lamps installed, propped into place behind the honeycomb with soft foam keeping it from falling back. It really was not supported or mounted, a problem that is worse with the 1130 I am currently restoring as it has no rear door for the display structure onto which foam would press. 

I developed a mounting system with two bits of steel channel brackets, threaded for a thumbscrew. These fit from the side, going over the Lucite holder that is glued to the honeycomb and screwed into the display structure. The thumbscrew tightens against the Lucite to hold the bracket in place. 

Soft rubber channel will be fitted along the left and right edges of my PCB and is secured under the lip of the channel, holding the board in place behind the honeycomb. The rubber doesn't arrive until the weekend and I also must wait for the special glue that binds the Lucite and Nylon together

LIGHTS CURRENTLY OUT OF THE 1130

There had been a flaw in the panel built by the prior restorer of this 1130 using my PCB and design. One of the SCRs had a lead that was not soldered onto the board, thus it neither lighted with a signal from the 1130 nor with the lamp test switch. I took the board out to repair that last week and now reassembled the bulbs onto the board and will install it using my new mounting method as soon as the last items arrive in the mail.

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