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Type: Posts; User: Hugo Holden

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    Check diodes D17, D18 and D19 & D20 for shorts. ...

    Check diodes D17, D18 and D19 & D20 for shorts.


    Check C25, C29 , C27, C31, C33. Also check the small value 330pF capacitors that are in parallel with D16, D17 & D18.

    There should be no power...
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    Thanks !

    Thanks !
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    S-100 connector geometry

    What is the official spacing between the connector pins on the S-100 card or socket. I measure close to 1/8 inch, is that correct ?
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    Smoke/heating of a component possibly D18 lower...

    Smoke/heating of a component possibly D18 lower right on the supply's output side. Check the diodes and capacitors there for shorts. I will look at the schematic and make some suggestions.
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    I don't think there is anything wrong with your...

    I don't think there is anything wrong with your philosophy about replacing old electros, though I put a different set of conditions on doing it, one is a time line slice. I replace most of them in...
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    Sounds sensible. That squeak for a second may...

    Sounds sensible.

    That squeak for a second may possibly be the power supply attempting to start but being overloaded, say, from circuits in the monitor overloading it (the typical failure here...
  7. I am impressed by Jim Rowe. He also seemed to...

    I am impressed by Jim Rowe. He also seemed to have a habit of thinking outside the box. In the 1969 issue of Electronics Australia that had the Intelsat image on the cover, Jim published a great...
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    I have listened to the sound. You need to try...

    I have listened to the sound.

    You need to try to identify the physical place where this sound is coming from. It has some features of high voltage arcing, which is worrying.

    (If a CRT has gas...
  9. Yes, that looks like the one.

    Yes, that looks like the one.
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    Hi, The first thing to do is not to jump to...

    Hi,

    The first thing to do is not to jump to conclusions about what could be wrong and start shotgun replacing parts, like capacitors. Every time you make an intervention you add some risk of...
  11. 1969 vintage computer with lever switches.

    I have attached a photo, unfortunately I had to downgrade the resolution so the file size was accepted.

    It is an interesting photo from inside Intelsat Labs, I would guess, in 1969, of the...
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    After some research in this area I would use a...

    After some research in this area I would use a product called Inox MX-3 because there are no issues with induced corrosion on metals containing copper & zinc (or any others) and it leaves a very very...
  13. Also, I just love the naming of computers and...

    Also, I just love the naming of computers and electronic components from the 1970's era.

    For example "Intertec Superbrain" very cool. And many other examples, companies like Signetics and...
  14. Wow, very impressed. I very much admire your...

    Wow, very impressed. I very much admire your never give up attitude. I'm am like that when it comes to repairs.
  15. That suggests to me that the designer, back in...

    That suggests to me that the designer, back in the 1970's, probably had a long history of designing in RTL and DTL and applied the idea to TTL.
  16. Looking at it, they paralleled two of the '05...

    Looking at it, they paralleled two of the '05 gates to make sure that the output got forced low, which actually would have been easier with a 74LS75 than the 7475 because the LS series have a higher...
  17. Interesting (unusual) Logic Technique.

    I'm in the process of building a replica of the Cromemco Dazzler. So I have been studying the circuitry to understand how it works and prepare myself for any technical issues that might eventuate.
    ...
  18. I would suggest, order the exact three small...

    I would suggest, order the exact three small transistors and the chopper transistor. Fit them at the same time (you have checked the diodes).And order a few extras.

    Load the 5V supply output with...
  19. One very interesting thing is to look at the way...

    One very interesting thing is to look at the way a 110/220V switched option SMPS was implemented in the 5155 computer.

    It also answers an interesting question, which could perhaps be posed in an...
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    I would like to experiment with this board. So...

    I would like to experiment with this board.

    So far I have experimented with the ALT 256 and ALT512 Boards and written articles on them, both of which I had to write my own software for.

    I...
  21. I agree, it can be done in steps so that the...

    I agree, it can be done in steps so that the ultimate spacing of the pins on each side of the IC matches the spacing of the socket entry points.

    The pushing down part you mentioned is very...
  22. Generally , wired in the 230V mode, the input...

    Generally , wired in the 230V mode, the input rectifier and filter system is wired as a full wave bridge rectifier (4 diodes) to charge the capacitor pair, but in 115V mode, it's wired (or switched...
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    Welcome. Apart from vintage computers, I got...

    Welcome.

    Apart from vintage computers, I got turned on to Japanese motorcycles when I saw the movie, in the 1970's, with Charlton Heston called the Omega Man, A post apocalyptic world where he had...
  24. The three associated transistors on the primary...

    The three associated transistors on the primary side are very important, two, acting as a latch limit the chopper's base current and the other the emitter current, so if they are not working the...
  25. The most likely reason why this would happen...

    The most likely reason why this would happen would be either the current rose too high through the chopper transistor, melting it's junction, or that it's collector voltage got exceeded. Previously I...
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