Thanks Dave for great work & documentation here! On 3/5/2024 10:04 PM, David Gesswein via vcf-midatlantic wrote:
Worked on straight 8. Reported problem was toggled in RIM loader wouldn't load the BIN loader tape. Verified issue was still occurring. Since we knew we had issues with connection to cards from last workshop cleaned all the processor cards edge fingers and backplane connector using paper/paper towel with contact cleaner. Battled them during restoration of the machine was 9 years ago due to storage conditions.
Didn't change symptoms so single stepped through the loader. Found the RTL (Rotate Twice Left) instruction didn't do anything. Traced it to bad transistor in R603 pulse amplifier in PB19. With transistor replaced and after figuring out I loaded the paper tape backwards the machine worked.
Processor sensitivity to motion seemed fixed and running finger down cards also didn't cause crash. Memory side was still sensitive so cleaned those also. Luck didn't hold so memory was non functional after cleaning. Tracing signals with scope found timing pulses missing from W300 delay line board. Inspection found cracked solder joints on both of the board. The delay lines are too tall so get pulled on when inserting or removing boards. Think that cracked joints were present and got worse when cards removed for cleaning. After resoldering Still not working. More probing and found one signal for write was not being generated. Inspected transistors on the W300 generating it and noticed one transistor lead was all rusty. Poked it and it disintegrated. With transistor replaced machine now worked.
Ran diagnostic set and reloaded demos and declared ready to go. Hopefully the problems on the W300 was causing some of the occasional flaky behavior.
All board cleaned except sense amplifier boards that had additional connections. Verified moving them didn't cause crashes. The boards plugged into the memory box also weren't cleaned since they are gold to gold. Also didn't clean front panel cable boards. If I was able to accurate count that high I cleaned 227 edge and backplane connectors. Each has 18 contacts.
We discussed enabling the 12 bit A/D that was installed in the machine when we got it. My memory was that wire(s) needed to be removed from the backplane to enable when I looked at it years ago. Maintenance manual says only cards need to be installed. Decision was to get it working removing wires if needed but I finished work on machine at 4pm Sunday so decided not a good time to mess further.
A/D can convert with 6 to 12 bits accuracy taking 7.6 to 56.6 microseconds. Input is 0 to -10V. We discussed some what demo to use that would be of interest to the public but not too gimmicky. Still thinking about it. Have Teletype where we can print results or text graph.
-- Douglas Crawford VCF Mid-Atlantic Museum Mgr InfoAge Science & History Museums 2201 Marconi Road Wall, NJ 07719