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Type: Posts; User: Hugo Holden

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  1. Replies
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    It can sometimes be hard to find genuine vintage...

    It can sometimes be hard to find genuine vintage old stock IC's, with all the fakes coming out of the far east.

    To get around this I have some trusted suppliers that often have very difficult to...
  2. It is almost certain that the resistor had the...

    It is almost certain that the resistor had the power supply across it, in other words feeding a dead short, to glow and burn up like that, otherwise something else would have likely heated up too,...
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    Thanks Mike, it had me a little concerned,...

    Thanks Mike, it had me a little concerned, especially since when I got the MM5204 module the clear windows were not sealed to light and I had wondered if they might have partially erased over the...
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    Solos rom question

    I'm in the process of building a replica personality module for the SOL-20 using 4 MM5204's.

    I have inspected the dump of a solos that came on a disc with a replacement personality module from...
  5. Ilpaninaro, I think Dwight and I are...

    Ilpaninaro,

    I think Dwight and I are distracting you from your current computer problem. We are just talking about the theory behind the capacitor and its circuit on the lower right of the...
  6. Though I think in this case there is only a small...

    Though I think in this case there is only a small voltage "window" where the capacitor is not effectively connected and there is no charge or discharge pathway. The equivalent circuit is close to a...
  7. Dwight, Off the topic of this thread (but...

    Dwight,

    Off the topic of this thread (but shouldn't matter as the OP's computer is fixed now) it is amazing what kind of interesting and oddball and sometimes downright brilliant circuits turn up...
  8. Dwight, As far as I can see with this circuit,...

    Dwight,

    As far as I can see with this circuit, maybe, the capacitor is charged by the transistors emitter current and would reach the peak value there, plus the average DC component there and...
  9. ...I should have said a 5A slow fuse after the...

    ...I should have said a 5A slow fuse after the capacitors are back to good order (I keep thinking of 230V systems) but as Dwight noted you should have a 5A fuse for 120V and a 2.5A fuse for 220V.
  10. One issue with these types of supplies is that...

    One issue with these types of supplies is that due to the massive capacity of the filter capacitors, at turn on there is a large initial surge current. The power transformer's secondary is...
  11. Replies
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    It wouldn't surprise me if it was the IC being...

    It wouldn't surprise me if it was the IC being defective. It is a bit of a hard ask for the IC , without a heat sink, to fully vertically deflect the crt, it takes 3 to 6 Watts of power to do it,...
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    So would I . And you can get really good analog...

    So would I . And you can get really good analog scopes for around $100, Hitachi ones of a 1980's vintage are still often very good and very reliable. I use the Hitachi V509 often, because it also has...
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    If a video monitor goes to a black screen, which...

    If a video monitor goes to a black screen, which I assume is what has happened, you need to start with the simple things first. For example has the monitor failed or is it just not being fed with a...
  14. Maybe when the computer powers up in an abnormal...

    Maybe when the computer powers up in an abnormal state, he could briefly short out the capacitor there and induce a good reset, to then see if it corrects itself ...What do you think ? Though now I...
  15. The tilt indicates the Yoke requires rotating. To...

    The tilt indicates the Yoke requires rotating. To do this the clamp screw must be loosened. Sometimes the white plastic tongues under it can be stuck to the neck glass, so if that is the case loosen...
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    I didn't count it up but on and off over about 3...

    I didn't count it up but on and off over about 3 months at weekends etc doing a little here and there making the card. Most of the time for me was figuring out the software side of it.
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    This particular pen is an interesting one. The...

    This particular pen is an interesting one. The buttons on it do not physically move, it detects the presence of the finger with a light touch. Also, in front of the photo-transistor, there is an...
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    Sol-20 light pen project

    I have just completed my light pen project for the SOL-20. The article describing the Hardware and the Software is here:

    http://worldphaco.com/uploads/LIGHTPEN.pdf

    A short video is here:
    ...
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    Of course I agree with you to that extent,...

    Of course I agree with you to that extent, however it has been my experience, that one way or another, a good piece of test gear that you can trust always fishes you out of a jam sooner or later and...
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    It would be pretty unusual for an IC like the...

    It would be pretty unusual for an IC like the MC1488 to be able to take out a switch-mode psu. Likely something else shorted out the supply rails (like a tantalum bypass cap) or more likely the psu...
  21. The continuity & beep function on the meter is...

    The continuity & beep function on the meter is not that useful for checking resistors are open or not unless you know what low ohms value for the meter is interpreted as continuity.The continuity...
  22. With the monitor switched off, and the meter in...

    With the monitor switched off, and the meter in resistance mode, simply put the meter connections on each side of the resistor.

    Due to possible loading effects or conduction via the diode, it is...
  23. Its good news that the E30 test point voltage is...

    Its good news that the E30 test point voltage is good at close to 30V. This means that the output transistor and its driver circuitry is definitely ok and that there is nothing of any extra...
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    In my humble opinion the best ESR meter on the...

    In my humble opinion the best ESR meter on the market today are these, a design by Bob Parker, its due to the type of design and the way a low amplitude pulse is applied to the capacitor also...
  25. I suggested exactly this way back in post #11: ...

    I suggested exactly this way back in post #11:

    "A less risky place to test, if your meter was not up to a 400V value, would be the E30 test point."

    Currently we know that the HOT appears to be...
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