I continued testing the power supply. It would work most of the time it was powered on and give the correct voltages, but then sometimes when it was powered it the +5V circuit breaker would trip. I managed to capture this on the oscilloscope The peak voltage was 5.16V and then the breaker trips and it goes down to around 1V. Time to keep investigating the G824 module to see if there is something wrong with it. (Michael from RICM has been very helpful with troubleshooting so far). I borrowed a nice mixed signal scope from the EE shop. It blows my HP 54200A out of the water. The +5V regulator is supplied by the +8V line. So Michael suggested looking at both of the lines as they power on to see what they look like. Not Tripped Tripped Above are the results of this. I measured the peak voltages for both lines when they tripped and didn't trip. The +5V line averaged around 6.6V when it didn't trip and averaged around 12V when it did trip. The...
There's a demo / video I've been meaning to record for a while, showing how a simple punch-in program and deft use of the auto restart feature can turn the PDP-12 into a musical instrument, thanks to the PDP-12's speaker (which clicks when the MSB of the AC changes state). Click "read more" to watch the video!
Today's task: get our Flip Chip Tester (FCT) up and running. For those who don't know, Flip Chips (in DEC parlance) are small circuit boards with a handle opposite an edge connector, about the size of a 3x5 card, that have a small number of discrete components on it. Each Flip Chip provides a specific set of components to a machine. The one pictured here is an M617, which provides six four-input NAND gates (two per IC). The Flip Chip would be inserted into a slot, and a wire-wrap backplane would connect it to power, ground, and upstream and downstream components. One of my favorite things to explain to students is how the PDP-12's CPU can quite literally be repaired. When FCs go bad, it's usually because some IC on the FC has failed. Of course, you can just swap out the whole FC (if you have a spare). However, they can also be easily repaired if you know what to replace and you have equivalent IC packages. Enter the Flip Chip Tester. Before he died, Warren Stearns pro...
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