Please help fixing this thing! PEMF machine

Discussion in 'General Electronics Chat' started by petit, Jan 24, 2013.

  1. petit

    Thread Starter Member

    Jan 24, 2013
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    Hi Guys,
    newbie here trying to fix a machine for a friend.
    I have here a PEMF (pused electromagnetic field therapy) machine from a good friend of mine, who use it to help horses.
    He bought this machine in the eighties in Germany, unable to find a diagrams, I cant even find the manufacturer online.
    So anyway, the machine powers up and everything seems to work correctly but, there is no output signal to the pads.
    The machine is supposed to send electric pulses to the pads, the pad has a coil inside, so if a magnet is place next to the pad you can feel the magnet pulsating, but that is not happening.
    The first thing i found was a shorted zener after the toroidal transformer, i changed it and it didnt make any difference, still not working.
    after that, i started troubleshooting the Vreg, long story short, i shorted the vreg and burned one of the IC's.
    i ordered all of them and i changed almost all of them until i fixed the mess i made, so all of the CD4000 and 1 of the 555 timer are new.
    after i fixed my mess, i havent been able to find the original problem, so i started changing parts like a mad man, i have change already besides the CMOS chips, two filter caps next to the transformer, two tantalum caps, one metal can transistor and a couple of diodes. i also check the SCR on the output side and is fine.
    wondering if anyone can give me a hand with this, i really appreciate it
    Thanks a lot!

    pemf1.jpg

    pemf1.jpg

    pemf15.jpg

    pemf2.jpg

    pemf3(front).jpg

    pemf6.jpg

    pemf18.jpg

    pemf15.jpg
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    This is interesting. Can a horse really benefit from a placebo effect when the horse doesn't know what the machine is supposed to do?
     
  3. petit

    Thread Starter Member

    Jan 24, 2013
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    I don't know what you mean about the placebo effect. Have you tried these kind of therapy with your own horses?just wondering...
     
  4. justtrying

    Active Member

    Mar 9, 2011
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    tricky problem... have you tried tracing the signal from the pad connector to see where it gets lost?
     
  5. petit

    Thread Starter Member

    Jan 24, 2013
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    last time I tried to trace the signal I end up burning one of the IC's! I don't have an oscilloscope, it's in my wishlist!
     
  6. justtrying

    Active Member

    Mar 9, 2011
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    what are you using? Oscilloscope would be handy here since signal is AC. If you try it again, make sure you measure against ground, it is crazy that traces are unlabelled, but if there is output at the connector, maybe its the pad?
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    How were you trying to trace it so that something smoked?

    Is this like a horse version of a TENS unit or something?
     
  8. petit

    Thread Starter Member

    Jan 24, 2013
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    I'm using a DMM, i don't know how to use an osciilloscope. The probe slipped checkinthe vreg. There is no output at the conector, it's not the pad, i have tried different ones. also the
    Red led is supposed to blink. i have also check the scr and is good
     
  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Have you measured continuity from the wire's connection to the circuit and the pad itself?

    Did you replace the IC that the magic smoke was released from?

    Does your meter have a frequency counter setting (usually marked Hz)?
     
  10. justtrying

    Active Member

    Mar 9, 2011
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    The fact that red LED does not blink is not very good, it shares a connection with the output. But I cannot see where the second connection from LED goes, it's like it isn't there, that is odd, also I see no resistor, so LED could be burnt out.
     
  11. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The PCB appears home made, so I doubt any schematics will be found. The front panel looks nice, though.

    Is the little jumper wire soldered on the bottom across the relay contacts (red box), or was that an etching error?
     
  12. petit

    Thread Starter Member

    Jan 24, 2013
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    Iwas testing the Vreg to see if i was getting 16V, so the probe slipped and i shorted ground to control, so it went full tilt over 20V and i burned one of the cd4000

    i dont know how those TENS unit work, this machine creates a electromagnetic field in the pads using Earth frequencies and their harmonics, those frequencies are believed to have healing properties.

    YEs, first thing i did

    yes, i was the last one i replaced, so all of the cd4000 are new.
    Yes

    The LED is fine, i tried it yesterday. and yes, it has a resistor, you can see in the pic attached. white/gray wire goes to red LED.

    I havent been able to find schematics, not even the brand, it looks like some kind of prototype.
    the little jumper wire was shorting one of the diodes, that's the output side. in the pic, is the diode closer to the red box. i took the bridge of already, it wasnt supposed to be there. my friend has another machine, i checked that one and there is no bridge. i dont know who did that, the only thing i know is that he took this machine to some place to repair, and they refused to fix it, because it was manufactured by a competitor. it looks like they put that there :eek:
    Thank you!
    pemf21.jpg
     
  13. petit

    Thread Starter Member

    Jan 24, 2013
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    Has anyone ever seen one of these?

    pemf20.jpg
     
  14. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    No I have not! :eek:

    If the marking is correct it is a 68nS delay line, which is basically a tiny coil of wire inside a ceramic holder. Televisions used to have delay lines in the nS range which were a coil of wire but usually were long rod with a coil around it.

    If that is a 68nS delay line then it will measure as a low resistance coil, probably in the tens of ohms. You can probably measure it in-circuit.

    If it is an extremely weird 68nF capacitor then you need to unsolder it, and out of circuit it will measure open circuit to DC and will measure as 68nF on a capacitance meter.

    The most obvious fault you could have is a failure of the final coil or the cabling to it (the coil that goes on the horse), either open circuit or a shorted internal connection etc that makes it behave like a short circuit.
     
  15. petit

    Thread Starter Member

    Jan 24, 2013
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    Thank you!

    they give me OL reading in ohmios. somebody told me maybe they are boxed MKT film capacitors 68nF, but he wasnt so sure.
    what do you guys think?
     
  16. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If it is on the high voltage side, it could be 68 nano-Siemens, which is a measure of conductivity rather than resistance. S=1/R, so it should measure about 15MΩ if that is the purpose.

    Do all the logic ICs have +5V/Vdd on their power pins? Is there a measurable voltage, or pulse frequency on any of the logic ICs? (Use DC and Hz/Frequency mode on DMM).

    If you can find where the oscillation starts, follow the traces from IC to IC to see where it stops.

    Does the LED Bargraph on the front display anything when you change the controls?

    Are you sure the replacement ICs you put in are oriented correctly (pin 1 to pin 1, rather than 5 (8pin) /8 (14 pin) /9 (16 pin) if flipped)?

    See if you can identify what parts do work, to help narrow down what isn't working.
     
  17. petit

    Thread Starter Member

    Jan 24, 2013
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    all of the CD4000 are new, but i can check if all of them have voltage.

    Yes, the green LED on the front display is working perfect. blinks faster or slower with the Hz knob and it light up more or less with the Gauss Knob.

    i have checked all of the 555 and all of them have input and output voltage

    i took pictures before i desolder them to avoid that

    what i havent checked yet is: 3 metal can transistors, all the caps (beside the ones listed below) , choke, pulse transformer, box square part, resistor.
    i have replaced already:
    two electrolitic caps, two tantalum caps, big can transistor next to choke, 3 cd4000, 2 555 timers, 3 diodes, 1 zener.

    i hace checked sucesfully: green big cap (10uF) Vreg 16V output, SCR, rectifier diodes with DMM
     
  18. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Look for where the voltage/signal does appear/vanish in the path between the IC pulse generator and the output. Is the toroidal transformer the input transformer, or a step up transformer for output? Use caution if the voltages are high.
     
  19. petit

    Thread Starter Member

    Jan 24, 2013
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    I found it on ebay Germany!
    25 x 68nF 0,068µF uF 63V RM5 Keramik Kondensator ceramic Capacitor
    25-x-68nF-0-068-F-uF.jpg


    The coil is fine, we have tried other coils. also the red LED would blink if there is output signal, even with no coil attached.
     
  20. petit

    Thread Starter Member

    Jan 24, 2013
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    How do i know whcich one is the IC pulse generator?

    yes, it's the imput transformer, two windings, 24V, one winding goes directly to pads, and the other goes to a strip of two zener 4.7 and a rectifier to lower to aprox 16V to feed the ICs (i think)
     
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