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  1. WHONOES

    CTEK MXS 3.8 repair

    No you don't need to figure out the input impedance at 20V, it should be the same for all voltage ranges and should be quoted in whatever documentation came with your meter. Secondly. Yes, remove the old device and then check.
  2. WHONOES

    CTEK MXS 3.8 repair

    No. When you set your DMM to a voltage range, it should have an input impedance of 10MΩ (or 1MΩ). This is a function of the voltage divider in the input stage. You should be setting your DMM to its 20V dc range.
  3. WHONOES

    What type of voltage regulators to use for IoT

    The noise on a switching supply can be reduced by either out a few turns of both output leads on a suitable ferrite ring core or by passing them through a cylindrical core that is designed to go round a cable. These can be very effective.
  4. WHONOES

    Switch for Piezo Injector

    How much current is required by you Piezo injector. A Mosfet is the right way to go. May I suggest you have a look at the link below for an understanding of what a Mosfet is. https://en.wikipedia.org/wiki/MOSFET
  5. WHONOES

    CTEK MXS 3.8 repair

    Sorry for the delay in responding. As the 2907 is a pnp device, the end of your detector that went to the FET gate should got to the Emitter and the end that went to the source should go to the base. There must be no other connections to the detector. Please note that the input resistance of...
  6. WHONOES

    CTEK MXS 3.8 repair

    You will need to connect to the base of the 2907 as that will be the bit being driven (hopefully) though that could be complicated by resistors connected to the base. You might be better off tracing that part of the circuit back to the controller pin and check there for a drive signal with your...
  7. WHONOES

    Hi from Tehran

    Nuclear power engineer wanting an electronic timer sounds a bit scary. Might be above board though?
  8. WHONOES

    CTEK MXS 3.8 repair

    If you have removed the 2907 transistor, you could check to see if it is being driven by the control circuit using the detector you built.
  9. WHONOES

    Normal resistors for High Voltage application

    Another thing to consider is that body contaminants from handling the resistor can significantly reduce its breakdown voltage. So, if you construct you "high voltage resistor" from a number of others, make sure you clean it thoroughly in alcohol and then pop it into a warm oven for 1/2 hour or...
  10. WHONOES

    Logic probe

    Had a go at simulating your circuit. The window comparators exhibit a lot of hysteresis which is part of your problem. Start off by ditching R6 and C1 then reduce R5 in value to 1K then replace the LM339 with a TL2272 and it should work. Edit: Or you could just use a 4 x 4093 gates paralleled...
  11. WHONOES

    Harman Kardon Sub TS10

    Have you tried putting a signal into it?
  12. WHONOES

    RF detector

    Why don't you fit a mic key switch that has an extra set of contacts and use that to illuminate your sign.
  13. WHONOES

    SONY "PROTECT" MHC-EC909iP

    Sounds like you have shorted an output once too often and wrecked an amplifier module. You probably need to get in there and do some measurements like the DC offset voltage of the amps.
  14. WHONOES

    Motor Speed Sensor.

    Shouldn't pin 6 of the 4013 in the second schematic be connected to ground?
  15. WHONOES

    Does this exist: a relay that defaults to its last setting?

    Why don't you simply make the DIP switches inaccessible once they have been set by using a cover or something. If you need to change the switches then remove cover etc, etc.
  16. WHONOES

    Switching Polarity of Electro-magnet.

    Yes it would be possible using some high current MOSFET's in an "H" bridge format. With some suitable logic, it could become a single switch operation.
  17. WHONOES

    I've decided to learn electronic repair :)

    You will need to learn some basic electronics first which is not a 5 minute job. Try a book called the art of electronics by Paul Horowitz.
  18. WHONOES

    Marantz 2015 Receiver Distortion

    OK but, don't go ripping stuff out willy-nilly. Lets see if we can get a handle on what's going on first. It's now early evening here so I am off out. Back on it tomorrow.
  19. WHONOES

    Marantz 2015 Receiver Distortion

    I meant between the bases.
  20. WHONOES

    Marantz 2015 Receiver Distortion

    A current limiter would be a good idea as it would be more flexible than a fuse. I would stay with the switch though. Do you have any small diodes at all? The 1N 4148's and 1N914's are signal diodes. That is the sort of thing that you want.
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