electromagnetic field therapy

[petit]

Re: electromagnetic field therapy

Anybody?

Thank you in advance

[redwire]

Re: electromagnetic field therapy

The pulse transformer only passes... pulses. The transistor must give 16V AC blips in order to get the signal to the SCR. If the transistor was on all the time, you would not get anything on the pulse transformer output- it does not pass DC. The transistor would get very hot too. The SCR only needs 0.6V to turn on but it is only on for the EMF pulse, which is fast and hard to measure. Two things you can do:

Pretend the SCR is actually getting triggered, and check parts downstream, like the diodes, red transformer, red led, coils and wiring etc. The SCR should have voltage on its anode. You can use a couple 12V lightbulbs (#194) in series to emulate the EMF coil.

2. If the SCR (gate drive transistor) is getting nothing, then I would guess one of the signals on the AND gate inputs is not working. The signal on "pin10: this one acts crazy between 1-5-14-and OL, 3.747hZ", I would trace that back.

I also noticed the 6 bigger resistors (like blue-gray-blue-silver?) which is 68Megohms. I think with the 10uF film (green) cap, it makes for a very long timer. This thing has a session timer, like 30 minutes? What does the G knob do?

[petit]

Re: electromagnetic field therapy

The pulse transformer only passes... pulses. The transistor must give 16V AC blips in order to get the signal to the SCR. If the transistor was on all the time, you would not get anything on the pulse transformer output- it does not pass DC. The transistor would get very hot too.

Hi!
correct me if i'm not understanding the purppose of the transitor NPN there,
on the pulse transformer, the primary winding has voltage at pin 1-ground and voltage at pin2-ground (same at both 16V) and a frequency of 160Hz at the lowest frequency setting of the machine. collector of the transistor is also connected to pin1, emitter goes to ground and base goes to the AND gate, so i assume when the transistor is triggered pin1 is shoted to ground so there is a voltage between pin1 and pin2 that way the pulse is accomplished, because right now i dont get any voltage at pin1-2. it is that the way it works?

The SCR should have voltage on its anode. You can use a couple 12V lightbulbs (#194) in series to emulate the EMF coil.

SCR anode is conected to ground

2. If the SCR (gate drive transistor) is getting nothing, then I would guess one of the signals on the AND gate inputs is not working. The signal on "pin10: this one acts crazy between 1-5-14-and OL, 3.747hZ", I would trace that back.

yeah i think that pin10 it's a little wierd too, maybe that one it's keping the transistor off being triggered right??? that pin goes to the frequency knob and also goes to one of the cd4013 that i really have no idea how they work i got to check those

I also noticed the 6 bigger resistors (like blue-gray-blue-silver?) which is 68Megohms. I think with the 10uF film (green) cap, it makes for a very long timer. This thing has a session timer, like 30 minutes? What does the G knob do?

you're spot on regarding those resistors and the big cap, sesion timer is 30 minutes!
the G knob is Gauss, intensity of the magnetic field from 40 to 100, but i dont know how it's that being regulated because i get 16V at pin1 and pin2 no matter where i set that knob
i'm getting an oscilloscope that way i can troubleshoot better
Thanks a lot for your help!

[budm]

Re: electromagnetic field therapy

SCR anode is conected to ground, are you sure?

[petit]

Re: electromagnetic field therapy

SCR anode is conected to ground, are you sure?

Pretty sure, check this pic, the trace is coming from toroid transformer

[budm]

Re: electromagnetic field therapy

If you look up the spec sheet, that pin on the bottom is Cathode (K), Middle pin is Anode, top pin is the Gate.
http://pdf1.alldatasheet.com/datashe...LA/2N4444.html

[petit]

Re: electromagnetic field therapy

If you look up the spec sheet, that pin on the bottom is Cathode (K), Middle pin is Anode, top pin is the Gate.
http://pdf1.alldatasheet.com/datashe...LA/2N4444.html

You're right, my bad. so anode goes to choke

[budm]

Re: electromagnetic field therapy

Yes, the Gate has a 33 Ohms resistor to Cathode, and a cap in parallel, the Gate gets the drive signal through a diode, like I said before, you can manualy trigger the SCR by pulsing the Gate using resistor between Anode and Cathode by touching and un touching th resistor between Anode and Gate, you said it did not do anything last time, that because you did not know which pin is Anode or Catode. It is hard when we get wrong information.
See post 51 for the diagram by redwire.

[petit]

Re: electromagnetic field therapy

Yes, the Gate has a 33 Ohms resistor to Cathode, and a cap in parallel, the Gate gets the drive signal through a diode, like I said before, you can manualy trigger the SCR by pulsing the Gate using resistor between Anode and Cathode by touching and un touching th resistor between Anode and Gate, you said it did not do anything last time, that because you did not know which pin is Anode or Catode. It is hard when we get wrong information.

nothing happens. 330 ohm resistor between gate and anode (middle pin)

[budm]

Re: electromagnetic field therapy

What dc and AC do you have at these two points?
By the way, this your drawing also show which pins are A, K, G for the SCR that you had marked.
I see why it does nothing, the power from the power transformer red wires flow through the transducer to supply the voltage to the SCR, so you have to have the transducer connected to the jacks.

[petit]

Re: electromagnetic field therapy

What dc and AC do you have at these two points?
By the way, this your drawing also show which pins are A, K, G for the SCR that you had marked.

yes, i did it right in that pic, but in the schematic is backward.
Do you mean between those two point or at each point and ground?
thank you

[budm]

Re: electromagnetic field therapy

Do you have the transducer connected? Just read between the two points as shown.

[petit]

Re: electromagnetic field therapy

Do you have the transducer connected? Just read between the two points as shown.

i tried with the transducer and without it. also in all settings. let me do that

[petit]

Re: electromagnetic field therapy

Do you have the transducer connected? Just read between the two points as shown.

56 VAC pad connected, 8VAC no pad 60hZ, 350mV vDC. in the backplate machine says ouput 2x24V

[budm]

Re: electromagnetic field therapy

"56 VAC pad connected" OK, that sound about right, now you should be able to pulse the Gate by connecting/diconnecting resistor between Gate and Anode with pad connected and see what happen.
By the way check the AC voltage between A and K, it should also have about 56VAC (no pulsing with the resistor).

[petit]

Re: electromagnetic field therapy

"56 VAC pad connected" OK, that sound about right, now you should be able to pulse the Gate by connecting/diconnecting resistor between Gate and Anode with pad connected and see what happen.

i already did like 10 minutes ago, with a 330 ohm resistor between gate and anode (middle pin) and nohing happened.
i did test the SCR and it gets triggered, but not with the resistor

[budm]

Re: electromagnetic field therapy

with the pad connected? If that is the case, that SCR is not turning on. Also what AC do you get between A and K?

[petit]

Re: electromagnetic field therapy

"
By the way check the AC voltage between A and K, it should also have about 56VAC (no pulsing with the resistor).

nothing, .5 VDC and nothing AC. yes pad connected

[budm]

Re: electromagnetic field therapy

That means the choke has open circuit!

[petit]

Re: electromagnetic field therapy

That means the choke has open circuit!

i think you got it!