I must state at this point that I am most decidedly not an electrical engineer, nor have I had any formal training in electronics. I do have some experience in building simple circuits to light LEDs in model airplane and rockets. I have a healthy respect for electricity, but I'm not afraid to experiment. Some of what I will describe here will be grossly oversimplified and the result of trial-and-error compared to what might happen if I actually knew what I was doing. I'm just documenting my learning process.
On the other hand, there isn't a lot of documentation for these panels. No instruction manuals or wiring diagrams have survived the past 35 years.
I knew from my experience with a segment from another control panel (see the thread here from collectSPACE.com) that these panels use 28V GE 327 aircraft lamps. In my previous project, I substituted 12V equivalents of the lamps. I decided to stick with 28V lamps for this project.
The other decision point here is: do I use the existing wiring, or do I use alligator clips to attach to the Roto-Tellite power posts like I did in my other project? In my other project, the wires had been clipped off when the display segment was removed from the larger panel. The panels I have now are complete and (apparently) undamaged - no wires have been cut, and they are attached to the original connectors.
Here you can see a portion of the back of the S-IB Operations panel. It appears relatively straightforward, since it is only comprised of indicator lamps in Roto-Tellite enclosures. The primary concerns here are:
- Do the lamps work? Which ones are burned out?
- Are there any short circuits in the wiring?
- How does the connector map to the lamps? (i.e., which holes in the connector are attached to which lamps?)
So, let's start simple, with the S-IB Operations panel. To assist in documenting the functions of the panel, I created an Excel spreadsheet that lists each indicator and its position on the panel. There are location designations stenciled onto the back of the faceplate. For example, the "LOX LOADING REVERT" indicator is in the upper left corner of the panel, and it is labeled "DS1" on the back of the faceplate. The numbers run consecutively along the rows (DS1 through DS8 on the top row, DS9 through DS16 on the second row, etc.). I transferred these designations to the spreadsheet.
Now, it was time to see what worked and what didn't. For my first simple test, I wired two 9V batteries in series, figuring that 18V would be enough to produce at least a little light from the 28V bulbs. My past project taught me that the center post of each Roto-Tellite enclosure was the ground and the two outside posts were +. I connected the battery negative terminal to a center post, and then clipped the power alligator clip to the power post on the "ALL ENGINES RUNNING" indicator (DS23). Success! The lamp lit, probably for the first time in 34 years!
Two more alligator clips were attached, to the IGNITION and the LIFT-OFF indicators, just for fun at this point. Fortunately, the lamps in these indicators were still good, so they glowed as well. I dutifully photographed the indicators as my inspiration for lighting up the panels.
At this point, the simplest thing to do would have been to touch the positive alligator clip to a post on each indicator to see which bulbs were still working and which were burned out. I opted to combine two steps here, by also seeing which pin on the connector corresponded with which indicator.
The connectors on these panels are "24-61" connectors, which are standard military hardware. Each hole has a corresponding letter. Unfortunately, the placement of the labels on the connector for the S-IB Operations panel was pretty inconsistent. The letters were often not immediately adjacent to a hole. This quickly became a problem as I worked my way around the connector, sticking a probe into a hole and seeing which lamp lit, then making notes on my spreadsheet. By the time I had worked about 1/3 of the way around the outside of the connector, I was losing track of which hole corresponded to which letter.
To aid in my documentation, I needed to make a diagram of the connector, invert the colors on my PC (to make a better printout), and then draw lines connecting each letter to its corresponding hole. That way, I could ensure that I was being consistent.
I found that as I worked around the connector from A-Z, the lamps lit in order, running horizontally. "A" corresponded to DS1, "B" to DS2, etc. A little lesson I learned, so that I wouldn't have to keep craning my neck from the back to the front of the panel, was to put a mirror in front of the panel so that I could see the bulbs light up while I stayed at the back of the panel.
I found that the bulbs in nine of the indicators were burned out and would need to be replaced. I may be able to move some bulbs from unused indicators to the ones that need new bulbs. A little spark told me that pins aa and bb were ground, which I should have determined first, before checking the bulbs!
So now I have the connector mapped to the indicators in the S-IB Operations panel. This was also documented in my spreadsheet.
As I mentioned, I would like to explore powering this panel through the 24-61 connector rather than with alligator clips. I will need to find out what kind of plug corresponds to this receptacle. They are labeled "Burndy MS3124E 2461S."
Next time: What does it mean?