Working on the issues with second digit of VERB display on DSKY panel

PROBLEM BROADENED AND THEN SHRANK

Initially my only problem was with the top horizontal segment (F) being absent. I did some touching and inspecting of the wiring and pin placement of the connector on the EL Panel and found that the top three segments were now blank - E, F and H.

After some probing of the wires I recovered the function of segment E, but F and H remain blanked. I already knew from logical analysis that it wasn't a problem in the Arduino or driver board. This is because the code to set up a digit is the same for all positions, the drivers that select the VERB area also control the working digit, and the drivers that control set or reset of the latching relays for the digits are the same for all digits. 

Therefore, any failure of the microcontroller or driver board would not affect just one digit position. Similarly the power supply is common for all digits and lighted segments. 

The likely suspects are:

• Wiring between Relay Module and pins for segments F/H
• Contact from the connector to the EL panel for those two pins
• Failure inside the EL panel, similar to how the COMP ACTY segment doesn't work
• Failure of relay contacts/wiring inside the Relay Module
• Failure of the relay itself to latch or unlatch

A look at the wiring of the relays in the Relay Module shows that failure of segment H is isolated to one relay and one set of contacts, but the failure of segment F would also cause segment M to fail, which we are not seeing. plus that relay drives segments E and N. This makes the failure of the relay latching extremely unlikely, and the only internal failure in the module the could explain this is double failure of two independent wires inside the module.  

I decided to do a binary search for the cause. First step was to use my voltmeter to determine whether the pins for F and H were receiving high voltage when selected. If so, the issue was in the EL Display Panel Module or connector If not, I had to look backwards to the Relay Module. 

The result was definitive. I had full voltage on all the segment pins for that digit, so they should all be lighting. However, they weren't. This excludes many of the suspects from above and leaves a smaller list 

• The miniWasp connector is not making good contact, even though the tail has voltage
• Something has failed inside the EL Display Panel Module itself. 

The three failed segments (yes, I am back to all three of E, F and H being blank) are not contiguous pins on the back of the module. Two are adjacent but the third is far away. The only closeness is that they are the three upper segments of the digit, top horizontal and the two upper vertical segments. There could be a common fault in the module causing this problem.

On the other hand, I had rocked the connector block slightly to see how difficult it would be to remove when I swap for the newer EL panel. The segment defect began after that action. Thus I could have a connector/connection problem. 

EXCITING ENHANCEMENT TO THE PROJECT

The owner of the DSKY parts I am using has kindly offered to drop off two additional modules. One is a second relay module and the other is a different and newer EL Panel Module.

The second relay module would necessitate significant additional wiring and six new transistor driver circuits. It also means I have to remove the EL Panel Module connector and add 35 more pins to light the five digits of the R1 field which I can now accommodate with the added relays in the second module.

The Arduino would need six additional output pins and some minor reprogramming.

The electroluminescent panel I am currently using is the first iteration of the specs. Among other characteristics that changed for the later production panels used on missions, the wavelength of the light is 5100 angstroms, a blueish-green color.

The versions that were installed in the actual spacecraft and ground simulators were shifted to a wavelength of 5300 angstroms, more of a yellowish-green.  I am excited to receive the newer EL panel module because I will then see the display exactly as the astronauts saw them. 

The Vintage Computer Festival takes place in a number of locations each year, including the VCF-WEST out here in Silicon Valley. Due to the pandemic, it won't be feasible to have the large crowds and interactions this year. The organizers have decided to conduct a virtual festival. There will be five minute videos in place of a physical exhibit.

In past years, I have exhibited my restored IBM 1130 mainframe and a life size working replica, a restored Xerox Alto, working teletypes, and talked about our restoration of an Apollo Guidance Computer, all in person. This year I will talk about the challenges, solutions and work involved in lighting up the DSKY panel.