LGP-30 Video Update

Cory Heisterkamp coryheisterkamp at gmail.com
Sat Feb 25 20:24:23 CST 2017

Some promising news on getting the LGP-30 up and running. With all systems stable, I tightened the head spacing on the three timing track heads (using brass 0.001" feeler gauges though I may have to go closer). This has resolved 'hanging' when hitting Start; it actually appears to execute for a cycle before toggling back to Stop for each press of the Start key. Of course without being able to see what's happening, it's likely just 'executing' garbage, but it's a solid first step.

In Manual mode, keystrokes from the Flexowriter now trigger a Stop/Compute toggle for each key entered and status neons on the flip-flop cards are registering unique bit patterns as each comes in. 

I put the scope on the (rebuilt) clock generator card and we have good 'T' and 'T-bar' signals propagating, but still haven't licked the 'digital display' issue. After further probing, the display began to stabilize and the single line expanded into the proper 3 for Counter, Instruction and Accumulator, and eventually a bit pattern emerged for the Instruction. No signs of data yet for Counter nor Accumulator, and there is an extremely pronounced 'throbbing' and visible refreshing. Here's a video: https://youtu.be/Nhya46V-l70

System timing looks spot on (top trace), but I also see some 'throbbing' when putting my scope on any of the three timing heads which seems a little strange to me (example on lower trace). Here's a quick vid: https://youtu.be/JjRKDWVUyjA

One thought is that the timing and short register heads are still too far off the drum surface for a solid signal, purely conjecture at this stage. -C

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