Wang LOCI-2A Restoration 2020
It turns on, but doesn't respond to any key presses. We should check the cable connections to the keyboard and the 1501A board.
Alex measured the power consumption at 1.4 Amps with a 121.5 VAC line voltage. The transformer is currently wired for a 115 VAC line voltage. We will consider rewiring it for a 125 VAC line voltage.
The fifth, eighth, and tenth NIXIs have the 4 number randomly illuminated. The seventh NIXI has the 1 number randomly illuminated. The ninth NIXI is not illuminated. The 1401A board decodes between two and four BCD bits to determine if a number segment in a NIXI should be displayed. Since we see some numbers randomly displayed in some of the NIXIs we likely have some diodes or transistors that are failing on the 1401A board. We should be able to measure the voltage drop across the diodes and transistors on the 1401A board to find the failing components. The transistors are S16393 parts and the diodes are 1N764 parts. The data sheets that I found say that the 1N764 is a Zener diode. Zener diodes are usually used for a voltage reference, and not as part of an input to a NAND gate. We have a spare 1401A board with one bad NIXI. If the spare 1401A board works we can use a NIXI from the bad 1401A to make a complete working one.
We tried the 1401A NIXI display board in the LOCI-2AC and it still had the same bad behavior. The spare 1401A worked OK in the LOCI-2AC except for the NIXI tube that we borrowed to fix the 1401A from the LOCI-2AC. We swapped one NIXI tube from the 1401A from the LOCI-2A into the spare 1401A, and installed it in the LOCI-2A.
We tried the 1501 Input Decoder Control for the Card Reader and Teletype board in the LOCI-2AC and it worked OK. We put it back in the LOCI-2A.
We tried the 1405A Miscellaneous Shift Pulse and Control board in the LOCI-2AC, and it responded to the PRIME key, but nothing else. We tried the spare 1405A in the LOCI-2AC. It worked OK so we installed it in the LOCI-2A. Now the LOCI-2A is showing signs of life.
All of the math functions are misbehaving. The register-to-register functions are picking up and dropping bits.
The W-register to S-register and S-register to W-register functions for all 16 S-registers look like they all work OK.
The LOCI-2 Applications & Instruction Manual includes lots of examples and descriptions of how the calculator works.