First Startup
The 720 has probably not been powered up for decades, so it is wise to review and test the power supply before powering up the full machine.
Power Supply
Electrolytic capacitors can certainly deteriorate over decades but it’s proven to be uncommon to find failed capacitors in vintage calculator supplies. Perhaps these expensive machines used only the best parts and these have aged well. Nevertheless, before startup these power supplies are tested with multimeter and if it’s easy enough to lift at least one side of a filter capacitor, those capacitors are tested.
In this case, all semiconductors and capacitors tested OK, so the power supply was brought up with small dummy loads on all outputs. All voltages came up well and after adjusting +5 and +12 they were:
- +5 = 4.99
- +12 = 11.99
- -5 - -4.94
- -12 = -11.14
Output waveforms were good and ripple < 10mV on all rails.
Machine Startup
First Memory Test
All logic cards were loaded and a 720A ROM image was slected.
Power-on and PRIME produced a working machine! 250+ TTL ICs, all over 50 years old, and all working. The Wang service manuals have a 60-line program that exercises and tests the core memory, this completes without error.
A working Wang 720A.