I removed wire lead remnants from holders. Then I soldered a 470 ohm 1/16W resistor to the + LED lead close to the diode, cutting off the remainder of the lead. A 26ga wire was soldered close to the diode on the - lead and the original LED lead snipped off. Another 26ga wire then was soldered to the other side of the resistor, close to its body, with its remaining lead snipped off. The assembly is fed into the nylon bulb holder. The 26ga wire ends are snugged against the side notches of the holder and cut short.
This was repeated 20 times today as I built up toward my goal of a full set of replacement bulbs for the machine. I would pull incandescent lamps, many of which I had originally borrowed from my own 1130 lamp assembly when I began the VCF machine restoration. My lamps were restored to my machine.
I removed and held onto any incandescent bulbs that were still working, with intact wire leads. The holders were thus emptied and ready to be used for replacement bulbs.
STILL HATE THE LIGHT PANEL DESIGN OF THE IBM 1130
The design of the display panel makes changing bulbs a very fussy and challenging task. The thin PCB with a group of up to sixteen bulbs attached is soldered to heavy wires on one side with little slack. It is barely possible to slide the first bulb out of the honeycomb cell because the wiring is so taut.
The attachment of the nylon bulb holder to the PCB is via a pair of pins. One is on the end of the SCR and the other is flexibly attached to the PCB by a pigtail. It is difficult to push the flexible pin into the holder at the same time that you are pressing the SCR's pin into the same holder.
Because of the flexible lead and the circular nature of the pins, the holder can and often is rotated a bit off plane. Each of the sixteen holders can end up with its own rotation and bend off axis from the honeycomb cell it must enter. Therefore, it takes quite a bit of wrestling, shifting the board various ways, until you can coax all the holders into their cells. Often it takes a screwdriver to force one or more holders into alignment.
Finally, the signal lines slide over a narrow pin on the rear of each SCR. The act of moving boards around to change bulbs puts stress on these and they can get bent over. There is considerable risk that one of the pins can break off of the SCR, rendering it incapable of displaying that signal.
As previously discussed, the incandescent bulbs have a tendency to have their wire leads snap off at the glass envelope. This can happen as they are twisted or bent during the act of inserting the PCB row into the honeycomb, but it has become much worse due to the corrosion of the spot where the wire enters the glass envelope as a consequence of aging.
I had designed and installed an entirely different mechanism to hold incandescent bulbs in place behind the honeycomb - it is installed on my personal 1130 as well as the machine owned by the System Source Museum. The frustration with the IBM designed parts drove me to this and many others have fought to a standstill with the lights of their own 1130 systems.
LOST AN SCR PIN WHILE WRESTLING THE SBR BOARD INTO THE PANEL
I populated the entire 16 bulbs of the Storage Buffer Register (SBR) with my LED replacement bulbs because it is essential I see the exact pattern of bits coming from memory as I debug this system. Having failed lamps in the SBR was a problem, and each pass changing incandescent bulbs introduced a few more snapped wire leads in other lamp positions.
During the process of wrestling the PCB, I had to pull against the wiring, bend the board against the wires enough to have the first bulb holder enter the first honeycomb slot nearest the wires. It then had to contend with the rotated and off axis holders, moving the PCB left, right, up and down as I tried to get all sixteen holders to fit into the honeycomb.
The signal wires that are plugged into the rear pin of the SCRs are easy to grab or move as you fight to get a good handle on the PCB for all the maneuvering. Sadly, one of the pins was bent one time too many and snapped off right at the surface of the SCR.
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| Spare SCR where I broke off the pin (center) |
PREPARING TO SOLDER A PIN BACK ONTO THE SCR TO RESTORE FUNCTIONALITY
I dug out some of the hard plastic that encapsulates the SCR assembly to expose enough of the pin metal inside the part that I could solder to it. I took a damaged SCR from my parts supply and tested the process, having snapped off the pin and then excavated before soldering. I was able to form a good connection between the broken off pin and the exposed nub.
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| Repair successful |
I am loathe to pull the board out again to work on the SCR needing the pin repair, so I am working out a way to hold the broken pin in place behind the PCB as it sits in the display panel, allowing soldering. The mechanical aspects of securing the broken pin and placing it in contact with the nub remain a challenge, but I am comfortable there is enough room to do the repair once I figure out the holding method.
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| Holding broken pin prior to soldering |
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