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  1. Replies
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    Thatís one of the references I was trying to...

    Thatís one of the references I was trying to find.

    I suspect the voltage will fall not rise if the capacitor fails open circuit though.

    Dave
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    Tom, My guess about the isolated transformer...

    Tom,

    My guess about the isolated transformer secondary and capacitor would be a harmonic filter of some description.

    If the capacitor goes short circuit - this will cause a high current to flow...
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    No, I haven’t tried this procedure before. I am...

    No, I haven’t tried this procedure before. I am just thinking out of the box :-)!

    It is good that you are seeing some coupling though.

    I do like Terry’s suggestion though to ground the other...
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    Yes, address $0000 looks fine. However, the...

    Yes, address $0000 looks fine. However, the interesting thing would be address $0001 (as stated back in post #164).

    The fact that the machine appears to work consistently is good, I am just...
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    106

    Hello again Ilpaninaro. When you say "works...

    Hello again Ilpaninaro.

    When you say "works fine" do you mean it powers up and the green light comes on only?

    This is an indication that the power supply works and the the internal 6502 has...
  6. Replies
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    221

    I have been able to find the schematics for the...

    I have been able to find the schematics for the SIM4-01 and -02 but not the -03.

    If they don't exist online, could I ask that you preserve them and see if you can get a copy to Al over at...
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    Welcome. We are a global mix of both hardware...

    Welcome.

    We are a global mix of both hardware and software.

    Plenty of people here that would welcome a new member!

    I am a member of a “funny” class where I design hardware and write system...
  8. Replies
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    Welcome to VCFED... Nice little card you have...

    Welcome to VCFED...

    Nice little card you have there.

    Let me get back to you presently about how much of a SIM4-03 you can test without a programmed EPROM...

    There are old designs on the...
  9. Thread: PET 2001 Cover?

    by daver2
    Replies
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    97

    There may be a small market for these types of...

    There may be a small market for these types of covers of course...

    Dave
  10. Replies
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    Thanks Jos, I will add some of my microcode...

    Thanks Jos,

    I will add some of my microcode logic diagnostic code to the specific addresses around where it is playing with these locations to see what is happening...

    I don't (therefore)...
  11. Replies
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    I think (:-)) I have put all of the...

    I think (:-)) I have put all of the infrastructure back in for interrupts now...

    I had to remove all of my diagnostic code within the I/O reads and writes - because otherwise the emulation was...
  12. Replies
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    It looks like the write to ROM from the microcode...

    It looks like the write to ROM from the microcode is intentional (unless I have misunderstood the I/D logic somewhere - which wouldn't surprise me of course).

    I have found the microcode:

    Write...
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    The timing should be locked to a clock pulse (one...

    The timing should be locked to a clock pulse (one of the 8 phases) and not left to the whim of a gate delay or pull-down capability.

    At that frequency - any type of 'slow' gate should really work...
  14. Replies
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    Hi Monty, Yep, I have that document. This...

    Hi Monty,

    Yep, I have that document.

    This is a listing of the microcode not the firmware itself.

    It passes the 4052/4054 determination OK (yes, I did have a screw-up here as well - but...
  15. Replies
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    >>> I know Dave doesn't like swapping stuff...

    >>> I know Dave doesn't like swapping stuff randomly, but

    It worked, so I would take it!

    Good to see that it passes my PETTESTER code (that is a pretty stressful test). However, I would still...
  16. Replies
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    Hi Monty, Yes and no... I keep having a go....

    Hi Monty,

    Yes and no...

    I keep having a go. I get a bit further and then hit a problem and get distracted by real paying work!

    I then go back to it. Find out what the problem is, move on a...
  17. Replies
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    yep, classic short circuit tantalum capacitor...

    yep, classic short circuit tantalum capacitor across the power rails by the looks of it.

    Once it has gone short circuit, it takes the voltage down with it. What happens after that depends upon the...
  18. Chuck, Thatís a nice description and avoids...

    Chuck,

    Thatís a nice description and avoids the Ďlazy writeí issue.

    Dave
  19. Thread: PDP11 GUI Crash

    by daver2
    Replies
    6
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    299

    I am guessing that a new build of PDP11 GUI is...

    I am guessing that a new build of PDP11 GUI is going to be required. Either because Microsoft have 'retired' a function or that the parameters have changed.

    I think you can get a bit more...
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    You need about 10 posts... From the trace back...

    You need about 10 posts...

    From the trace back in post #123 I think we concluded that address $0000 was OK and things started to fail at address $0001.

    From that trace I believe I could see a...
  21. Replies
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    Sorry guys, I got sidetracked with real work...

    Sorry guys, I got sidetracked with real work today. I had a quick look this morning, and then the problems started that demanded my attention.

    I will have a look tomorrow, but I agree that there...
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    There is a schematic around - but it may be in...

    There is a schematic around - but it may be in one of the other Zimmers directories - and the transformer fitted may be different to the schematic (in terms of pin numbers).

    Measure the AC voltage...
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    That sounds like the logical approach! Buy...

    That sounds like the logical approach!

    Buy what you really want to keep that interests you when it appears for 'sensible money' - and sell off some of the other stuff to pay for it...

    Dave
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    And I thought you said your collection was large...

    And I thought you said your collection was large enough now?

    Does that mean you are going to start selling things off and replacing them with others as you find them?!

    Dave
  25. Replies
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    Yes, weird... >>> I lose track... which memory...

    Yes, weird...

    >>> I lose track... which memory location is currently being tested?

    That's why I am interested on the previous WRITE cycle.

    There appears to be two (2) read cycles 'bunched...
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