electromagnetic field therapy

[tom66]

Re: electromagnetic field therapy

This thing looks like a prototype made in someone's garage, not a professional product.

[petit]

Re: electromagnetic field therapy

UPDATE!
I cut the wierd bridge, wired the bad zener with clips and.. . now it's not blowing fuses but still no signal.
checked the zener and is shorted.
put another one, and again the zener is shorted. i checked both before
what it can be?

[budm]

Re: electromagnetic field therapy

OK, on my post 17 (unit not plugged in), use the Ohm meter to check the resistance using black probe to the Ground as I indicated, then measure resistance on each pin of the regulator and ground. Post the result, make sure to write down what the meter show on the screen , I.E. 1, 1K, or 1M. Also recheck the other 2 diodes to make sure they are not shorted out.
The unit uses some Tantalum caps which when they go bad, they will short out.

[petit]

Re: electromagnetic field therapy

OK, on my post 17 (unit not plugged in), use the Ohm meter to check the resistance using black probe to the Ground as I indicated, then measure resistance on each pin of the regulator and ground. Post the result, make sure to write down what the meter show on the screen , I.E. 1, 1K, or 1M. Also recheck the other 2 diodes to make sure they are not shorted out.
The unit uses some Tantalum caps which when they go bad, they will short out.

Ground-1= infinite
Ground-2=4.15k
Ground-3=3.64k
first zener 0.654v
rectifier 0.503v

[petit]

Re: electromagnetic field therapy

maybe the new zener couldnt handle the inrush current from the toroid transformer? zener 1n4732 1W
the original one is mzp4732
thanks!

[petit]

Re: electromagnetic field therapy

any idea?

Thank you!

[budm]

Re: electromagnetic field therapy

So far nothing yet, the current must be really high to take ot the Zener that is why I have you check for short.

[petit]

Re: electromagnetic field therapy

So far nothing yet, the current must be really high to take ot the Zener that is why I have you check for short.

Thank you for taking the time Bud

i've attached a pic of the problem in case anybody has any idea about it.
Thank you

[redwire]

Re: electromagnetic field therapy

Can you redo the Vreg ohmmeter (and diode test) readings, with (-) on Pin1 or the heatsink bolt, (+) on:
Pin 1 Comm (GND)
Pin 2 IN
Pin 3 OUT
Pin 4 CONTROL
<TAB is Comm.>
-----------------------

It's one of three scenarios, kinda need to narrow it down:

1. The Vreg is shorted
2. Some IC the Vreg supplies power to is shorted
2. The filter capacitors are shorted

You can try replacing parts until it's fixed, and blowing fuses, which is a bit expensive.

I would take a small DC power supply and inject power into the Vreg (+ after the zeners, to Vreg IN pin2, and - to pin 1 COMM or circuit ground i.e. heatink). The Vreg looks set up to make 15.6VDC output (4k7&10k), so normally you'd need >18V feeding it. But if there is a short somewhere, even feeding in 5V or 9V is going to make something get hot. This is how I would track it down. I'd use an old wall adapter, around 500mA. Maybe other people here have ideas that are not so harsh.

The 1W zener is a bit small, a 5W part (like a 1N5337) would do much better (after the short is fixed, of course)

I'll look at the jumper difference tomorrow.

[petit]

Re: electromagnetic field therapy

Can you redo the Vreg ohmmeter (and diode test) readings, with (-) on Pin1 or the heatsink bolt, (+) on:
Pin 1 Comm (GND)
Pin 2 IN
Pin 3 OUT
Pin 4 CONTROL
<TAB is Comm.>
-----------------------

It's one of three scenarios, kinda need to narrow it down:

1. The Vreg is shorted
2. Some IC the Vreg supplies power to is shorted
2. The filter capacitors are shorted

You can try replacing parts until it's fixed, and blowing fuses, which is a bit expensive.

I would take a small DC power supply and inject power into the Vreg (+ after the zeners, to Vreg IN pin2, and - to pin 1 COMM or circuit ground i.e. heatink). The Vreg looks set up to make 15.6VDC output (4k7&10k), so normally you'd need >18V feeding it. But if there is a short somewhere, even feeding in 5V or 9V is going to make something get hot. This is how I would track it down. I'd use an old wall adapter, around 500mA. Maybe other people here have ideas that are not so harsh.

The 1W zener is a bit small, a 5W part (like a 1N5337) would do much better (after the short is fixed, of course)

I'll look at the jumper difference tomorrow.

Thanks for your help!

Vreg readings are:
Ground-2=OL
Ground-3=4.15k
Ground-4=3.64k

first zener=0.652V
second zener= shorted
rectifier 0.504V

i just ordered this from radioshack
NTE 5115A - Zener Diode - 4.7V 5W #:NTE5115A
i havent blown a fuse since yesterday after i put the slow blow 1A, but every zener i put there has died. isnt that wierd? two zener in series and just that one blowing... and both are 4732.
should i check the filter caps?

[redwire]

Re: electromagnetic field therapy

I drew a partial schematic of the power section. I'm not 100% sure of the transformer connections. It seems to have an SCR flyback-converter to generate the EMF pulses.

The jumpered diode would only shut off the red led, so whoever did that was out to lunch.

Your ohmeter readings around the Vreg do not show a short-circuit.

[budm]

Re: electromagnetic field therapy

If you leave out the Zener diode that keeps shorting out, will it still be blowing fuse? I believe you are having two problems.
The fuse blowing more likely to be caused by over current draw in the SCR circuit.
The shorting out is another problem in that regulator section. i cannot see components in this section that the regulator circuit is feeding will draw enough current to cause primary current to go up more than one amp in the primary side.
By the way, you are using 1.25A fuse, not 1A fuse, right.

[petit]

Re: electromagnetic field therapy

I drew a partial schematic of the power section. I'm not 100% sure of the transformer connections. It seems to have an SCR flyback-converter to generate the EMF pulses.

The jumpered diode would only shut off the red led, so whoever did that was out to lunch.

Your ohmeter readings around the Vreg do not show a short-circuit.

i'm so impressed! Thanks a lot for your help redwire!
about the jumpered diode, the red led was working all the time with that bridge there, all the control panel works, the led blinks as fast as the pads are supossed to pulsate.
do you have any idea about that shorted diode going bad everytime i turn on the machine? i have blown four of them already...
i have ordered another one but instead of 1W is 5W with higher surge tolerancy in case that was the problem.
i took some more pictures with a lamp behind the board, that way the pic shows the pcb traces.

If you leave out the Zener diode that keeps shorting out, will it still be blowing fuse? I believe you are having two problems.

i dont know what would happen if i leave that diode out, i dont think the machine would work at all , but i can try tomorrow

The shorting out is another problem in that regulator section. i cannot see components in this section that the regulator circuit is feeding will draw enough current to cause primary current to go up more than one amp in the primary side.

The machine is not blowing fuses anymore since i put the slow blow fuse (i was using the fast acting). i couldnt find the 1.25A locally so i'm working with 1A slow blow. but i havent blown any of those yet, what is blowing now is the darn zener!

Thanks a lot!

[budm]

Re: electromagnetic field therapy

OK, I thought it is still blowing the fuse.

[redwire]

Re: electromagnetic field therapy

petit: just to be clear, it burns up zeners always and blows smaller fuses- with or without the EMF coils connected?

The jumper should not make a difference, unless some of the diodes are zeners. I can't see the numbers but they look like 1N4003's?

Can you test the metal can transistor beside the red and brown cubes. It drives the SCR pulse transformer and if it shorted, it would overload the Vreg.

[petit]

Re: electromagnetic field therapy

All right, now i think i really messed it up!
i got the new diode, installed, this one is not blowing, i tried with no pads, with the pads, nothing was blowing, but still no output.
so i had the brilliant idea to check the vreg while the machine was working, one probe to pin1, the other probe to output, the probe slipped, i think i shorted ground to control, wierd noise and now the front panel is not working like is suposed. it doesnt blink.
any idea on what i burned? any of the IC?
i didnt damage the vreg, i checked the voltage and it reads around 24v input and around 16v output

The jumper should not make a difference, unless some of the diodes are zeners. I can't see the numbers but they look like 1N4003's?

yes, they are 4003 all of them

Thank you

[redwire]

Re: electromagnetic field therapy

uh, if you short the Vreg control pin to ground, it goes full tilt, over 20V The chips on the board are rated to 15-18V max. (555 timers, CD4000 etc.) so one of them might be damaged. That's too bad

For the time and money, I would get some solder wick, remove an IC, put in a socket and then a new IC. With no schematic it's just too hard to trace. The 4000 series chips are fragile and I would do them first.

[petit]

Re: electromagnetic field therapy

uh, if you short the Vreg control pin to ground, it goes full tilt, over 20V The chips on the board are rated to 15-18V max. (555 timers, CD4000 etc.) so one of them might be damaged. That's too bad

For the time and money, I would get some solder wick, remove an IC, put in a socket and then a new IC. With no schematic it's just too hard to trace. The 4000 series chips are fragile and I would do them first.

Thank you redwire!
i'll do that then.
i was checking online and all of the IC are cheap. some others i can't find them, i'll post pictures of those to see if anybody can help identify them, to look for a replacement.
I also was checking for a replacement for the 2N4444 SCR and the cheapest replacement is more that $20! i hope that one is not damaged too!

[petit]

Re: electromagnetic field therapy

Hi Guys!
Today i had the time to play around a little with the machine, i received the IC's in the mail yesterday so i remove one by one, put in a socket and then a new IC, i started with the cd4000 as redwire suggested, so third one i removed was the bad one, the one all the way to the left.



after i had the machine working the way it was at the beginning, i replaced the can transistor next to the big red box, but still no luck.
at this point, do you guys have any idea which part could be the problem?
i also order two of the three 555 timers, should i replaced those also?
I checked the SCR 2n4444 with the ohmeter and is working fine

Thank you

[Uranium-235]

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