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  1. (*steve*)

    My next project? What do you think?

    I picked up a very sorry HP410C. I'm not sure if it's been wet, or in a corrosive atmosphere, or what. The handle seems to have quite a bit of surface rust. I wonder what it looks like inside?
  2. (*steve*)

    Trying to assemble a high voltage low current PSU

    300V at 0.5mA will deliver a maximum power of 0.15W. That is well within the capabilities of something powered by batteries or a low voltage DC plugpack (wall wart). At a current of 0.5mA it is also unlikely to kill you (but it wouldn't feel pleasant to be shocked by it). The old disposable...
  3. (*steve*)

    Need help finding power source for solenoid

    I would advise you to look for an electronic strike plate. These are designed for this application. That solenoid may not be designed for continuous operation.
  4. (*steve*)

    How can I connect this microphone and recorder to AA-batteries?

    Do you have a link to any documentation?
  5. (*steve*)

    cap tester repair

    I reviewed an article recently that spoke of the experience of those who worked for Heathkit "fixing" problems caused by people's kit construction. The observation was that, very frequently, problems were resolved simply by fixing poor soldering -- dry joints being a common issue. Another...
  6. (*steve*)

    cap tester repair

    You replied to yourself. I originally suggested that you check all the wiring to ensure there wasn't a construction error, however you assured us that it was once working correctly.
  7. (*steve*)

    TIP120 Transistors Appear Charred

    They look fine from what I can tell (but it's hard to see to much detail on a phone). What are you measuring (is it voltage)? Do you have a diode test range on your meter? Use the diode test range with the power off and the filter capacitors in the power supply discharged. You should read...
  8. (*steve*)

    Flyback transformer testing and replacement

    I have been flip flopping about the operation of this part of the circuit. The overall operation is very likely how I have described, but this part of the circuit may do a number of things. One purpose may be to protect the base-emitter junction of Q9. Another may be to prevent Q9 from being...
  9. (*steve*)

    IC324 help please

    And his direct message reply... This is exactly what we don't do.
  10. (*steve*)

    Flyback transformer testing and replacement

    The operation is probably something like this: If Q10 is turned off, the circuit is enabled. Current through R41 turns on Q9. The current through Q9 and the transformer (pins 2 and 4) storing energy in the increasing magnetic field As the transformer saturates due to the current in the pin...
  11. (*steve*)

    IC324 help please

    We are not going to do your homework. What do you think the answers might be, and why? Perhaps after you've had a go we can comment on whether your reasoning is sound.
  12. (*steve*)

    Flyback transformer testing and replacement

    Best of luck
  13. (*steve*)

    cap tester repair

    Hmmmm... That's not wildly high, but it may be worth replacing. I doubt that it is causing the current problem, so it's not something I'd do right now (unless you have a replacement 1.5M resistor on hand). Try the tests that Edd is suggesting. I'll take a deeper look at the schematic. There...
  14. (*steve*)

    Oscilloscop trace at sceen bottom

    It is likely to be a mechanical failure (broken solder joint, crack in a PCB, or even a fractured component). Probing around with a plastic, glass, or even wooden rod may allow you to find a location that is sensitive to pressure. Assuming the prodding stick is a very good insulator (don't use...
  15. (*steve*)

    cap tester repair

    Lost for words?
  16. (*steve*)

    cap tester repair

    Ok, those readings make a lot more sense. I would be interested in the resistance of R6, a 1.5MΩ resistor, possibly connected to pin 8 of the 6BN8.
  17. (*steve*)

    cap tester repair

    Nice :-). Better than my bodgied together hack.
  18. (*steve*)

    cap tester repair

    Here is a full schematic, apologies that some parts don't exactly line up. I'm sorry, this is not the best quality. You can see more by zooming in to the pdf. I would still use the PDF for reference reading some of the small print! Now to add some voltages... (and I bet you had the...
  19. (*steve*)

    cap tester repair

    I wouldn't lose heart, it's a relatively simple piece of equipment, and in a worst case you can replace a lot of the components that might have gone bad for a pretty small price. Let me take another look at the schematic and I'll see if I can see other reasons for the very high plate voltage on...
  20. (*steve*)

    cap tester repair

    Ok, clearly the voltages on the 6E5 are waaaay off. This may be because the resistor between pins 2 and 4 is the wrong value, or the triode part if this tube isn't biased correctly. The heater must be ok, because you're getting a display. It is possible that the capacitor connected to the...
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