electromagnetic field therapy

[petit]

Re: electromagnetic field therapy

I don't know if anyone has gotten around to this, but have you thought about replacing all the caps? if this thing was built in the 80's and hasn't been used, the caps might be completely dried out

I skimmed the thread the best I could to see if there is any mention of cap readings but unless you take them out of circuit usually you aren't going to get a proper reading. and yes that goes for the green cap in the middle

Hi Uranium,
that might be a good idea, i've been hesitant to start replacing everything, because when i took this machine i tought it was something simple, because the machine stopped working suddenly, it's not that it was stored for years.
First thing i found bad was the second zener in the string after the transformer, so i thought i had found the problem, but i didnt.
do you think i should start replacing caps? which ones first?
Thank you

[petit]

Re: electromagnetic field therapy

Hi!
anybody know what is that part with 68nS printed?
there are two of them after the SCR gate and before the choke that look pretty toast

Thank you!

[redwire]

Re: electromagnetic field therapy

On the pcb I see a few of those oddball black square parts and guess that they are boxed MKT film capacitors 68nF Siemens? They are pretty reliable and look okay, no toast.
I'm not sure what the unit is doing now? Is it still blowing fuses? Do you get +15V from the Vreg? You put in the bigger 5W zeners, changed a few cmos chips and I'm not sure where things are at.

For the two blue blob capacitors (tantalum) can you read the #'s off, as they can short if over-voltaged.

[petit]

Re: electromagnetic field therapy

I'm not sure what the unit is doing now? Is it still blowing fuses?

not blowing fuses anymore but still not working.

Do you get +15V from the Vreg?

last time i checked, after i burned the IC, i was getting 16V

You put in the bigger 5W zeners

yes, i did put the one that was blowing all the time and no problems after that

changed a few cmos chips and I'm not sure where things are at.

i change all of the cd4000, the last one i changed was the bad one, i also changed one of the 555, with no luck fixing the no output problem.
also changed metal can transistor next to big red box.
i ordered a replacement for the SCR 2n4444 but the one they sent has less lead spacing, so is useless.

For the two blue blob capacitors (tantalum) can you read the #'s off, as they can short if over-voltaged.

The big one says:
+68
+16V
W Germ.

The small one
+6.8
+25V

Thanks a lot!

[redwire]

Re: electromagnetic field therapy

When you say it doesn't work - the red/green led's come on? (and) there is no pulses felt in magnetic coils?
At this point, you have to poke around with an oscilloscope and trace the signals, or keep guessing and changing parts.

[petit]

Re: electromagnetic field therapy

When you say it doesn't work - the red/green led's come on? (and) there is no pulses felt in magnetic coils?
At this point, you have to poke around with an oscilloscope and trace the signals, or keep guessing and changing parts.

Green light next to the control knobs come on, the red led next to the output doesnt (it's wired right to the output) and still no pulses in the magnetic coils.
i dont have access to an oscilloscope, i have it in my wishlist!
i'm going to change some of the capacitors and hope to get lucky...
Thank you!

[petit]

Re: electromagnetic field therapy

Replaced blue tantalum caps and and filter caps next to Vreg and still nothing. i tested the old caps for capacitance with DMM and they gave the specs value. i replaced them anyway.
do you guys think i should replace the SCR next to the output? it's like $20. expensive part for a guessing game.
should i desolder it and test it out of the circuit?

[budm]

Re: electromagnetic field therapy

I believe the LED should be blinking even if the SCR is not installed since it looks like the pulsing is done by the 555 Timer IC that I think I see on the board for the Hz SWITCH SELECTING circuits, please see if it has one. You can look for the pinout andfunction of the 555 to see if it is oscillating or not. Look at output 3 with your meter, the voltage should be swinging up and down at low frequency as set the Hz knob.

[petit]

Re: electromagnetic field therapy

I believe the LED should be blinking even if the SCR is not installed since it looks like the pulsing is done by the 555 Timer IC that I think I see on the board for the Hz SWITCH SELECTING circuits, please see if it has one. You can look for the pinout andfunction of the 555 to see if it is oscillating or not. Look at output 3 with your meter, the voltage should be swinging up and down at low frequency as set the Hz knob.

i can see 3 555 timers, one next to the speaker, another one next to the three red square caps on the left and another next to the big green cap.
The green strip blinks and the speaker change the beeping frequency when i move the HZ knob. that's why i think the timer in charge of the oscillating is working.
the red led is wire to the output with a resistor in series.
what about that choke box? and the brown box next to it?
Thank you!

[budm]

Re: electromagnetic field therapy

"the red led next to the output doesnt " so this LED is connected to the output port that goes out to the magnetic tranducer? You should be able to see pulsing at the Gate of the SCR if it is being driven by the low frequecny.

[petit]

Re: electromagnetic field therapy

"the red led next to the output doesnt " so this LED is connected to the output port that goes out to the magnetic tranducer?

Yes, Red LED is conected to the output

You should be able to see pulsing at the Gate of the SCR if it is being driven by the low frequecny.

How do i check that? red probe to gate and black to catode? sorry for the newbie question but i dont want to messed it up again!

[petit]

Re: electromagnetic field therapy



output side, grey/white wire goes to Red Led

[budm]

Re: electromagnetic field therapy

Yes, per REDWIRE post51 drawing. I do not know where the transformer for the Gate drive is on the board.

[petit]

Re: electromagnetic field therapy

SCR is working... i tested it out of the circuit with a "flashlight SCR tester".
any idea?
Thank you!

[petit]

Re: electromagnetic field therapy

I was thinking maybe one of the 555 timers is damaged? the one that trigger the pulses to the pads?
the machine has three, one for the speaker, another one for the green LEd's and the other for the pads?????

[budm]

Re: electromagnetic field therapy

You can check at the output pin (pin3) to see any action on all of them.

[petit]

Re: electromagnetic field therapy

You can check at the output pin (pin3) to see any action on all of them.

I just checked the 555 and the results were 16V in two of them and 3V in the other. is that possible?

[budm]

Re: electromagnetic field therapy

What DC voltage do you get at pin8? If you are seeing 16V at output pin 3, then the VCC on pin 8 must be even higher which means that the Voltage regulator IC is putting out too much DC, redwire had indicated that it should not be higher than 15V or 16v on thread 49

[petit]

Re: electromagnetic field therapy

What DC voltage do you get at pin8? If you are seeing 16V at output pin 3, then the VCC on pin 8 must be even higher which means that the Voltage regulator IC is putting out too much DC, redwire had indicated that it should not be higher than 15V or 16v on thread 49

16.19V on pin8 on all of them. i double check and still getting 3V in that one. could be that the problem? damage 555 timer?

[budm]

Re: electromagnetic field therapy

May be, it depends on how the 555 is set up to be, the one with 16V out put may not be setup as Oscillator. You can put your meter to AC mode and take the reading at the output pin of all 3 555 to see what you read.