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  1. KrisBlueNZ

    HP 1741A Oscilloscope

    It would have been better to have them all in a straight line. If you'd used 1/4 watt resistors, nine of them might have gone end-to-end across the space on the board. Then you would just make sure they were raised somewhat off the board. That's how I would have done it. But as long as you...
  2. KrisBlueNZ

    HP 1741A Oscilloscope

    There's a very high voltage across that resistance. If you mount all the resistors on a single board, that voltage will appear across that board, so make sure the board is rated for that voltage. If you use stripboard, or any other board with a copper pattern on it, remove all the copper apart...
  3. KrisBlueNZ

    HP 1741A Oscilloscope

    Right. As Steve said, the voltage is the problem. The top of that resistor has about 2200V on it, and that's far too much for a normal resistor, which is why they used that big thing originally. That's why I suggested nine 3.3M resistors - they will have about 250V across each one. Normal 1/4W...
  4. KrisBlueNZ

    HP 1741A Oscilloscope

    OK. You won't be able to measure that resistor; normal multimeters can't measure resistances higher than 20 megohms. You can measure it using the 120V rail but you'll have to do a bit of work. First, check that your multimeter has an input resistance of 10 megohms when measuring voltage. This...
  5. KrisBlueNZ

    HP 1741A Oscilloscope

    OK. It's difficult to diagnose this circuit. U1 is not easy to test, so let's assume it's OK. Another component that's likely to fail is R13. I think it's the big cylindrical red thing directly left from the top of the green oval in that picture in post #88. Can you lift one end out, confirm...
  6. KrisBlueNZ

    HP 1741A Oscilloscope

    Leave the HV MULT disconnected. It won't affect the reading, and it's safer that way. Standard voltmeters go up to 1000V. This test point is supposed to be more than twice that!
  7. KrisBlueNZ

    Simple power supply questions

    If you're worried that the charger may not be a proper match for the batteries, put the whole lot outside, or do it in the garage. I had a pack of NiMH AA cells overheat on me while I was developing a charger board and I can tell you that it doesn't take long for them to overheat, and when they...
  8. KrisBlueNZ

    HP 1741A Oscilloscope

    OK. It sounds like it might be the transformer. I don't know what would cause that problem in a transformer. I expect that dampness getting into it might do it. The other possibility is a problem with the regulation. The HVPS circuit may be generating too much voltage. That would explain why...
  9. KrisBlueNZ

    HP 1741A Oscilloscope

    Pretty low, unless it is getting hot. But the AC voltage from that secondary isn't low... In post #24 you said "Pins 3 and 4 (which feed a 48V line) has 58.8V". 58.8V AC is plenty high enough. Well, you should try again. I didn't suggest it for fun! Find the wire from the ultor cap on the side...
  10. KrisBlueNZ

    HP 1741A Oscilloscope

    You said the +120V rail is 11.99V but you meant 119.9V, right? Interesting that the 156V rail is now equal to the 120V rail. This implies a problem in the circuitry around CR3 and Q11. Can you measure the voltages on both ends of R18 (relative to the 0V rail, i.e. the chassis)? Interesting...
  11. KrisBlueNZ

    Simple power supply questions

    Yes, the battery can't handle that much load current. A battery can be (very roughly) modelled as a voltage source with a series resistance. This resistance is called the battery's internal resistance. You can think of a resistor as a tension spring. This spring is hooked on a point 9.6 feet...
  12. KrisBlueNZ

    HP 1741A Oscilloscope

    OK, first try disconnecting the "HV MULT" unit from the board. This will be an external block with a thickly insulated wire emerging from it that goes to the "ultor cap" on the side of the bulb of the CRT. Try powering it up in a darkened room and look for a purple corona anywhere on the HVPS...
  13. KrisBlueNZ

    HP 1741A Oscilloscope

    CR8 is not critical. The NTE519 will be fine. The NTE287 and NTE288 look OK as replacements for MPSA42/92. They're probably actually identical, just rebadged.
  14. KrisBlueNZ

    Simple power supply questions

    If the monitor takes 5~24V you could power it directly from the batteries, couldn't you? If the regulator output voltage is dropping when the load is connected, then either the regulator can't supply enough current, or the batteries can't supply enough current to the regulator. Can you measure...
  15. KrisBlueNZ

    (woo woo) transformers 1:5 ratio - were to buy

    Are you implying that you think some "over-unity" or "free energy" devices DO work? I strongly disagree. We only learn from stuff that DOESN'T work if we can figure out WHY it doesn't work, and then MAKE it work. A design that WILL NEVER work is only a source of frustration, never education. I...
  16. KrisBlueNZ

    Hunting specific, possibly rare tact switch, please help. DJ CD Player

    You can try mouser.com, and you can try Googling mail order electronic components. If you can't get an exact match, yes, you could try modifying something similar.
  17. KrisBlueNZ

    Temporary on/off switch and second switch turns all off

    I can't help you with that. Post a new thread in the Electronics Projects section.
  18. KrisBlueNZ

    HP 1741A Oscilloscope

    Hah! We have a Vetco here in New Zealand, but they are... veterinarians! I don't see MPSA42 and MPSA92 on their web site though. Maybe they just aren't listed there. They do list the NTE51 so you could replace Q2 offboard if you want.
  19. KrisBlueNZ

    HP 1741A Oscilloscope

    No problem. Well, I'm not sure what's going on with the circuit. But this back-and-forth is a very slow way to figure it out, so this is what I suggest. First, R1 could be faulty. You can replace it with a 33k 5% resistor; it doesn't have to be 33.2k and it doesn't need to be highly accurate...
  20. KrisBlueNZ

    CRT Sync Symbol

    Sure, but phase of what?
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