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I've got a transformer that I think is blown. It is for a $$$ machine at work.

Thus far I know it takes both 110/220V in and is supposed to output 35V, 5V, 12V and -12V.

I have confirmed 120V into the transformer, but beyond that, I don't know what to test.

All output pins on the circuit board read 0 to .3V when tested to ground, all output pins have infinite resistance when shorted to ground or shorted to each other (a few read in the Mega Ohm range, all others were infinity).

The transformer coil itself has 7 pins on each side. The high voltage side appears to be wired to 4 pins, the output side is wired to all 7 pins.

I don't have good access to the circuit board (yet) because it's riveted to a metal chassis. Rivets are easy to drill out, so the shouldn't be a big problem.

I've got a 6 pack for a knowledgeable person to troubleshoot this for/with me.

Scott

Are all the output voltages you mentioned DC values? Dou you know what the power requirements are for what it feeds?

Honestly, it sounds like a standard computer power supply could take care of most of that.

In any case I would imagine that a diode in the bridge went bad, or possibly an electrolytic cap if it has any of those in there.

Are there any markings on the transformer? Best case is you get a hit off http://www.digikey.com/ for it.

Pictures of the parts in question could help too.

When it's powered do you get any voltage off the low side?

Scott,

Staying at a very basic level:

I'm trying to pin down whether this is a linear power supply versus a switching power supply. Both can be used in old and new products so it depends on the design needs.

Is it cord connected (ac power cord with an inlet receptacle) or "hard wired"?

Was it capable of changing between 120 or 240 input without changing the input wiring location (i.e. was it like a modern computer power supply with a "universal" approach to input/output circuitry?)

Does the 120 volt wiring go directly to the transformer or is there a bunch of circuit components on the primary side of the transformer?

Does the transformer have a laminated core versus does it look like powdered metal?

Does it look relatively big for the load versus surprisingly small?

Is there a lot of circuitry on the low voltage side of the transformer or do the various outputs go somewhere else with minimal circuit components on the power supply board?

Did the equipment suffer some sort of "tramatic" event that might have overheated the transformer and caused a fuse or thermal protector to open?

I don't know where you work. Is this a medical product? Does it have some sort of certification mark like UL or CSA? If so does it mention a standard number such as 60601?

One concern is that if it is medical equipment the transformer requirements are very special and very important to safety as well as operation.

Finally, with that many outputs it is very likely to be application specific, especially if this is a low volume product.

_________________
Dick Rasmussen

FS 50 2018 Mustang GT

Get a part number and a picture if you can.

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In need of car.

Disconnect the primary side of the transformer from the 120/240 input power and any associated wiring. than read thru the transformer with the ohmeter. you should see a reading considerably less than a megohm. I suspect that the primary is burned up (open) because you've lost all voltage. An open in the secondary of a transformer will normally not kill all voltage, but only those in the effected winding.
The reason you must disconnect the primary is to prevent the ohmeter from reading through any associated circuits on the input power side.
iF you need more claification call me at 698 8539

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2004 C5(415whp,390ft/lbs),
1997C5,1997Trans Am, 1986 C4,
1990 Miata, 1976 MGB,1997 Protege, 1989 MR2

Is it the mass spec?

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Has no responsibility whatsoever.

The robot arm for loading samples into the microwave.

The repair quote over the phone started at $4000, and that was before any diagnosis. Another tech suggested we just buy a new one as the current model is "vintage."

Apparently, his version of vintage is different than mine.

I'll take pictures today.

Scott

I've not looked at this thing for the last week. Here are the pictures I promised.

http://home.earthlink.net/~celica73-3/supply/

I hope that you don't have a lot of Suzuki couplings in your future.

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Has no responsibility whatsoever.

Scott,

I don't claim to have practical power supply experience. But I did do a lot of UL power supply projects in my younger days so there is a chance I've got this correct . . .

Due to the very large number of components, including filtering components on what looks like the primary (120 or 240 vac) side of the transformer combined with the small size of the transformer, my first educated guess it that this is a "switching regulator" power supply. What this means is that 50 or 60 Hz input is rectfied and then switched at high frequency (20KHz or more) before going to the transformer.

This type of power supply is much more efficient, much more compact, and can provide better voltage/current regulation than traditional linear power supplies. They started with the space program, then big computers, and have worked their way into cell phone and electric shaver AC adapter/chargers.

However, there are a lot of filtering, control, and feedback components in both the primary and secondary curcuits which can fail. Bottom line there is a very good chance that the transformer isn't the problem. Unless there is evidence of obvious component failure (what would a failed electrolytic capacitor like the big blue one look like compared to new?) it probably will take a pro with the correct test equipment. Even though you measured 120 volts at the transformer, that may not be correct for proper operation if it is a switcher.

_________________
Dick Rasmussen

FS 50 2018 Mustang GT

I agree with what Dick has said. Capacitors of age go bad, and the fact that you have basically no output anywhere likely means the thing has shut itself down. Once you remove it from the chassis, any decent electronics tech could swap out all the capacitors, starting with a handful of the biggest ones, pretty quickly and cheaply.

It sure *looks* like a switching power supply to me, and the fact that it's riveted like that means whoever made it LIKES making a lot of money on service by just swapping out large components.

Do you know how much current capability you need on each of the listed output voltages? If you have even a vague idea on that and are willing to re-wire some stuff then you could likely just replace this unit with some combination of off-the-shelf units from somewhere like Jameco. That 35V output is going to be the tricky one, though. Everything else is easy. That one can be conquered easily, too, if you don't need it at much current, but somehow that seems unlikely.


--Donnie

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My Blog

Scott a couple things.

I agree its a switching power supply. The transformer would be bigger if it were a linear supply.

I'm going to assume you've checked the fuses??

Do you have an oscilloscope at your facility? With that an a voltmeter you can do a reasonable job of troubleshooting the supply.

Do you have a manual and schematic for the board? If so it may have test points called out. If it does it should have at a minimum the voltage expected and, if not DC, perhaps the expected waveform.

If it were me I'd verify that you're getting voltage to the primary (line cord) side of the transformer. I'm guessing since you said no voltages anywhere it will flunk this test. If not, read on.

Then right at the pins of the transformer check for output voltages. They probably won't be the correct voltage but if you have any voltage at all the output pins then you can be sure that the primary is OK and that the windings on the secondary side (the side with the lower voltages you listed) are all OK.

Let me know how you do with these tests (send me a note directly to ron.e.spencer@gmail.com) and I'll try to walk you through some other tests. Can't promise anything......

Ron

Ron thats basically what I told him a week ago. He's getting power to the primary and no output on the secondary. It doesn't matter what type of xfmr it is even a switching xfmr will give secondary voltage with power applied to the primary.

_________________
2004 C5(415whp,390ft/lbs),
1997C5,1997Trans Am, 1986 C4,
1990 Miata, 1976 MGB,1997 Protege, 1989 MR2