Marc nicely sums up this project with this line: "It's an IC but in discrete form!" On the same theme, he later says, "Who needs a logic analyzer when you can do a visual debug with neon bulbs?"
Very cool. Lots of troubleshooting and repair lessons in this video:
-- Again we see the benefits of paper manuals. (Todd K7TFC commented astutely on this under yesterday's post.)
-- 2N2222s to the rescue.
-- A surprisingly large number of bad transistors (6?) found. Why did they go bad?
-- Marc repeatedly says, "Let me poke around." Poking around is often important. Mark fixes the reset line after poking around. He is not sure HOW he has fixed it, but he has... by poking around. Sometimes this happens. Thank God for small favors.
-- Marc has some fancy HP board extenders. I am jealous.
-- He also has a cool de-soldering tool. More jealousy. Want one.
-- Marc's understanding of how the HP engineers had to put one of the flip-flops "on the edge of stability," and how his 'scope probe was capable of disturbing this stability.
-- Remember that those Nixies are TUBES with enough voltage on them to really zap you. So be careful in there. This is an especially dangerous mix of transistor tech and tube tech. With transistors you can work on them with the rig fired up. With tubes, well, you have to be careful.
Part III tomorrow.
Discrete, YES! it's the opposite of Concrete. Discreet, Not necessarily so. :) Yankisms ... :(
ReplyDeleteFrom years of messing about with regens, superregens and (save me!) even RTL digital, I've found even presence or absence of Soldering flux can considerably alter a circuit's stability!
ReplyDeleteMessing about with GHz frequencies and nanosecond timings are likely to incur similar effects.
These videos were so interesting, several things reminded me of ham radio:
ReplyDelete1) seized grease - Ten Tec PTO problems related to grease
2) comb generator - can anyone remember crystal calibrators ?
3) Nixies mixed with transistor circuits - the Heathkit SB-104 used those cool Beckman displays which were gas discharge, I remember Todd, WB9HJG, saying that mixing high voltage and low voltage like that was a design choice looking for trouble :)
Best Regards,
Chuck, WB9KZY