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#1
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Quote:
Henry |
#2
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74ls20
The days you could run to the local store and pick up a 7420 are definitely over. How sad. No Kenbak programming this weekend. I ordered several 74**s online and they will probably arrive on Wednesday.
The LS versions are 0.52 a piece and so I simply had to order another $ 20 of stuff I do not really need to prevent the $8 shipping. But I was good: I didn't end up with 50,000 LEDs. |
#3
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Too bad. Better luck next time!
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#4
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Everything works
To make a long story short: see the attached picture of IC25. The problem had nothing to do with a faulty 7420 as I mistakenly claimed before. It really is this simple. Only some people (Geoff) find this faster than others.
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#5
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Hmmm, that looks familiar
Congratulations, I'm glad you got it running. What are we up to now, three running Kenbak-1 Series-2 machines? Four, including Grant. That makes us a more exclusive group than owners of original Kenbak's |
#6
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Quote:
So, have you run any of the examples from the manual yet? Grant |
#7
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Finding the error
I suspected the IC52 and I replaced it with the one in IC77. Then the problem of all the LEDs being lit constantly was gone, and I wrongly concluded I found the answer. But it just accidentally worked because I took out IC77. When I put in a new 7420 at IC77 it was back.
Since I swapped IC25 and IC41 before (with the 7400 from IC99 remember), the only thing I could think of is that IC25 was upside down which can easily be detected by checking the voltage at 7 and 14. Only then I saw 1.5 V at pin 14 of IC25 and started disassembling the machine. Warned by Geoff, I carefully checked the board after soldering and back then I found two similar incidents. But apparently overlooking a third. |
#8
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Assembler
So exactly how do I go about using AS? I want to write a program to calculate E (Euler's constant). The series converges rapidly and you only need to maintain the sum and the term.
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#9
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Finding the error
I suspected the IC52 and I replaced it with the one in IC77. Then the problem of all the LEDs being lit constantly was gone, and I wrongly concluded I found the answer. But it just accidentally worked because I took out IC77. When I put in a new 7420 at IC77 it was back.
Since I swapped IC25 and IC41 before (with the 7400 from IC99 remember), the only thing I could think of is that IC25 was upside down which can easily be detected by checking the voltage at 7 and 14. Only then I saw 1.5 V at pin 14 of IC25 and started disassembling the machine. Warned by Geoff, I carefully checked the board after soldering and back then I found two similar incidents. But apparently overlooking a third. |
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