electromagnetic field therapy

[petit]

Hi Guys,
newbie here trying to help a friend out. i apolige in advance if i posted in the wrong subforum.
I have here a PEMF (pused electromagnetic field therapy) machine from a good friend of mine, who use it to help horses to heal for tendon and bone problem.
He bought this machine in Germany in the eighties, so there is no diagram available, 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.
After some troubleshooting (i'm just a hobbyist trying to learn as much as I can about electronics) I found a bad zener diode mzp4732 conducting both ways, you can see the bad diode just on top the black cap.
I ordered, replaced and when I hit the power switch the fuse blew .
I did desolder the diode, got another one, put it with aligator clips and another fuse blew.
then I put it in opposite direction trying to check all the possibilities and again another fuse. So for now i'm out of ideas, if anybody can help me with some ideas I would gladly appreciate it.
Thanks in advance!

[ratdude747]

Re: electromagnetic field therapy

Moved from General computer discussion.

[redwire]

Re: electromagnetic field therapy

Are you sure this is a 110V or 220V device?

The zener, (if it's between the two caps and the heatsink) is in series with the neighboring diodes. It seems to function as rectifier/power-feed for the UA78G voltage regulator (on the little heatsink). The diodes would lower the incoming AC to a voltage the Vreg can handle (max. 40V) and something the black electro's could take. What rating are the caps? A shorted zener might over-voltage them.

With no zener, if fuses still pop, then you have a problem elsewhere.

I would check all the diodes, by the black caps and the output? cable (gry/red/vio wires), and what is the big heatsunk part below the big red box (mains EMI filter?). It looks like an SCR or triac. They do short easily.

Don't use the yellow metal C-clamp to hold down the toroid transformer if the center bolt is in. It can act as a shorted turn and make the transformer draw more current than usual.
Hope this helps a bit.

[Jack Crow]

Re: electromagnetic field therapy

P
You pick the winners don't you.

I think we need more information and photos about this thing.
Can you take good high quality close up photos?
Sometimes a more experienced tech can see things a new guy would miss. It's happened here before.

Don't forget to include images of these 'pads' you call out.
If they are some kind of E/M transducer a shorted winding will do bad things to your generator.

If it's a coil kind of device I can give you some basics on how to see if it's working or at least compare the two of them.
(Im assuming two pads per generator.)

Did you get an 'owners manual' with it?
In English I hope.
A careful read of it may shed some light on the matter.

Same for your vet friend, have him write up the way it's used and post it here.
Also what is a similar unit on the market.
Might be able to glean some useful information from competitors write ups. Similar machines made for the same task.
(Just for giggles I looked up electro convulsive therapy machines.
Seems there are two vendors in the US and they trash each others products on the web sites!)

Might also help to know just how it died.
The truth, not the usual stories we get from clients.
Did they do something stupid like trying to heat coffee with it?
Leave it out in the rain, plug it into 220vac?
You can usually get clients to tell the truth about equipment failure, if it will save them some money.
It's a trick that will save you a lot of hours fooling with equipment.

Some place in the world is someone who works on this thing.
Might have to dig more and nose around a bit.
Photos of the front panel, OEM's name and if there is a plate on the back with the tech data? Some have FCC ID numbers or UL data. Might be able to back into the service info that way.

What concerns me is that ugly wire bridge on the bottom of the circuit board.
Is that photo of the 'stock' condition of post repair?

Can you test the zeners you tried? Are they blown too?
That is as we say a clue.

Also look around for schematics and service data on similar units.
Might get a clue there as to what you have.

You did get on the right board for this.
Many members here live in Europe and may have a connection or know someone who 'worked there'.
Give it a few days.

Im going to flag this post with an 'e mail subscription' and wait for some answers.

If all else fails, your going to have to check each part on the board.
Some can be tested in circuit, some will have to be removed.
Again good photography will insure you put everything back the way it was.

I'm hoping your the first to look at it since failure, and not the last. Just fixed a car audio amp that someone else fixed and failed at. No joy there.

Much luck
Jack Crow in Virginia.

[budm]

Re: electromagnetic field therapy

Front panel pictures of the unit, back panel, how the transducer is connected to the unit. The board looks like home made board since there are no designators at all for the component on the board.
Also pictures of how the wires from the Toroid transformer are connected to the board.

[diodo49]

Re: electromagnetic field therapy

Home Made like tortillas? mmm...

[ratdude747]

Re: electromagnetic field therapy

Front panel pictures of the unit, back panel, how the transducer is connected to the unit. The board looks like home made board since there are no designators at all for the component on the board.
Also pictures of how the wires from the Toroid transformer are connected to the board.

Looks homemade or given the vintage, a prototype/short run. The PCB layout was done by hand.

Also a bit of bodge work... I see a lot "jimmied" components (axial parts soldered between component terminals, bare leads intentionally shorting pads, etc.).

I kinda doubt you will find a schematic... unless, of course, it was out of a magazine or other publication.

[petit]

Re: electromagnetic field therapy

Hi guys,
thank in advance to those who chimed in!
i took some close up pictures this morning like Jack Crow suggested yesterday.

Are you sure this is a 110V or 220V device?

Hi redwire, yes, it is a 110V/60 hz device

The zener, (if it's between the two caps and the heatsink) is in series with the neighboring diodes. It seems to function as rectifier/power-feed for the UA78G voltage regulator (on the little heatsink). The diodes would lower the incoming AC to a voltage the Vreg can handle (max. 40V) and something the black electro's could take. What rating are the caps? A shorted zener might over-voltage them.

the caps are 220 microF 40V, and yes, both zener are in series and both are 4732 4.7V. the next diode is a regular 4003. also what's up with those zener in the same direction and both being the same value? to me the second zener would only see the fixed voltage from the first, am i right?

I would check all the diodes, by the black caps and the output? cable (gry/red/vio wires), and what is the big heatsunk part below the big red box (mains EMI filter?). It looks like an SCR or triac. They do short easily.

i have checked those three diodes around the black caps and the bad one was that one (the one on top of the black cap).
i have also check those wires, it was the first thing i did because the only problem with the machine was not getting signal to the pads, everything works, even the led in the front cover blinks as fast as the pads should, that's why i though the problem was in the output.
the diodes next to the red box looks fine, but the one next to the red box has the brigde under, so i dont know what they were trying to achieve there.
in the big heatsink below the red box there is a 2N4444

Don't use the yellow metal C-clamp to hold down the toroid transformer if the center bolt is in. It can act as a shorted turn and make the transformer draw more current than usual.
Hope this helps a bit.

good catch! i didnt think about that!

You pick the winners don't you.

I think we need more information and photos about this thing.
Can you take good high quality close up photos?
Sometimes a more experienced tech can see things a new guy would miss. It's happened here before.

Don't forget to include images of these 'pads' you call out.
If they are some kind of E/M transducer a shorted winding will do bad things to your generator.

If it's a coil kind of device I can give you some basics on how to see if it's working or at least compare the two of them.
(Im assuming two pads per generator.)

i attached a pic of one of the pad, the machine can work with one or two pads, in order to use two pads there is a extension cord with two outputs.

Did you get an 'owners manual' with it?
In English I hope.
A careful read of it may shed some light on the matter.

no luck finding a manual or diagram anywhere

Same for your vet friend, have him write up the way it's used and post it here.
Also what is a similar unit on the market.
Might be able to glean some useful information from competitors write ups. Similar machines made for the same task.
(Just for giggles I looked up electro convulsive therapy machines.
Seems there are two vendors in the US and they trash each others products on the web sites!)

there are some similar units on the market, in fact i own one machine, it's similar, it looks like an upgraded copy, it's not nearly as powerfull as his, but i can take a look inside to see if i can find any similarities.

Might also help to know just how it died.
The truth, not the usual stories we get from clients.
Did they do something stupid like trying to heat coffee with it?
Leave it out in the rain, plug it into 220vac?
You can usually get clients to tell the truth about equipment failure, if it will save them some money.
It's a trick that will save you a lot of hours fooling with equipment.

i dont know how it died, i can ask him, he just told me it stoped getting signal to the pads, i'm gonna ask him to see if he can elaborate more..

P
What concerns me is that ugly wire bridge on the bottom of the circuit board.
Is that photo of the 'stock' condition of post repair?

you have good eye! i have the same concern,i dont know what that bridge is doing there either! that is the diode next to the red box, it doesnt sound very smart putting a diode, and then make it useful soldering a bridge under.

P
Can you test the zeners you tried? Are they blown too?
That is as we say a clue.

the first zener i soldered blew, the second one i tried with alligator clips in series with the neighboring diodes, and this one survived. but the fuse didnt

P
I'm hoping your the first to look at it since failure, and not the last. Just fixed a car audio amp that someone else fixed and failed at. No joy there.

That concerns me, i'm not the first one messing with it. he took this machine to some place to repair, and they refused to fix it, because it was manufactured by a competitor, they were not allow to touch it, so i hope they didnt damage the machine on purpose, just to make him buy one from them.
he has another identical machine, so i think i'm gonna take some pictures of the working one to check discrepancies, i have been hesitant about start messing with the working one, because he makes a living with theses machines, so i cannot afford an accident that could damage that one.

Looks homemade or given the vintage, a prototype/short run. The PCB layout was done by hand.

Also a bit of bodge work... I see a lot "jimmied" components (axial parts soldered between component terminals, bare leads intentionally shorting pads, etc.).

I kinda doubt you will find a schematic... unless, of course, it was out of a magazine or other publication.

it really looks homemade, but he paid more that 4 grand in the 82 for it, just the machine with no pads, but he has helped hundreds of animals with it to recover from bone fractures, dogs and cats after being hit by cars...the machine really works.

thanks a lot for your help!

[petit]

Re: electromagnetic field therapy

sorry, forgot the pics!




















have a great day!

[budm]

Re: electromagnetic field therapy

Is there any labeling on the Toroid transformer? I see two red wires and two black wire connected to the PCB, any info on the transformer as to what they are?
Also that red module, do you have the name and P/N on the top of it? I cannot see it clearly.

[petit]

Re: electromagnetic field therapy

a picture is worth a thousand words!
yes two red and two black to the PCB
Thanks!
Ruben

[budm]

Re: electromagnetic field therapy

OK, I am trying to draw up the diagram. Can you please circle the Zener diode you have replaced?

[petit]

Re: electromagnetic field therapy

there you go!
thank you

[budm]

Re: electromagnetic field therapy

Please the picture.
Hmm, I draw up the connection, that Diode should be regular rectifier.
The mzp4732 is printed on the Diode? How about the other 2 Diode closed by?

[petit]

Re: electromagnetic field therapy

Hi,
i didnt replace them myself,
that is why i think those people messed it up! i just spoke to my friend and he told me the machine was in their custody for some time and after that they refuse to fix it for him.
what do you think about that wierd bridge shorting that diode? (pic pemf11)
thanks a lot!

[petit]

Re: electromagnetic field therapy

yes, mzp4732 is printed in both, the top ones are both the same in series, and the next one is a regular diode 4003 and after that split to the capacitor and to the voltage regulator

[budm]

Re: electromagnetic field therapy

OK, please look at my redlined based on how the two diodes are installed.
That RED modue is slome kind of power suply module (not 100%) that are being fed by the second power supply.
Did this unit work at all before you have done any repair to it?

[petit]

Re: electromagnetic field therapy

the machine powers up, and start the treatment, when i hit the start button, led diodes blink but nothing happen in the pads.

[budm]

Re: electromagnetic field therapy

But right now it is blowig the fuse? The same size anf type of fuse being used? since Toroid transformer has VERY high inrush current.

[petit]

Re: electromagnetic field therapy

Yes, right now blowing fuses, after i replaced the bad zener diode (the black one is the one that came, that i put back for the picture)
i put a lower rating fuse, the original one is 1.25A, but couldnt find that one locally so i put a 1A. I have the 1.25 ordered. maybe that is a posiblle problem beside the diodes?