So far, I’ve tested power rails and they appear to be reasonably good. The SCELBI power supplies provide +5 and -9. In addition, components on this card need -5 and +12. The -5 is generated on board using a series of voltage dropping diodes connected to the -9 supply. The +12 is generated with the little converter that can be seen mounted on top of the board. That converter has been documented in a few previous posts. The -5 supply sits at something like 5.6, which is a bit on the high side, but I’ll just go with it. The +12 looks pretty good, as it is sitting at 11.8. Voltages could change a little bit in actual operation as the testing was done without a running clock. I’ll definitely keep an eye on that as I move forward with more testing.

I am expecting the crystal that I need to arrive next week. The installed crystal is something I had on hand in a parts bin. It is something like 3.6 Mhz, which I figured is close enough that I could use it to check clock generation and general performance of the timing portions of the circuit.