SMPS High Frequency Transformer technical Details

[r.raslan]

Hi,
I would like to get to know more information about the high frequency transformer that is used in switch mode power supply circuit such as:
How it is made? Why does it have many leads? (I mean: should not be like a normal low frequency transformer from the pins point of view but it was designed to handle high frequency voltage?)

How should I test the transformer (verify its condition)?
Thank you in advanced!

 

[cowboybob]

Do you have a schematic that can be shared with us? It would be helpful.

How many pins, and in what arrangement, does your transformer have?

What test equipment do you have access to?

 

[r.raslan]

Do you have a schematic that can be shared with us? It would be helpful.

nop, but I am talking in general.

How many pins, and in what arrangement, does your transformer have?

I do not have schematic to my SMPS board but the transformer it has 16 pins. It has multi outputs such as +12 and +5 and other outputs that I do not know what are their rated voltages.

What test equipment do you have access to?

DMM with frequency range measurement

 

[cowboybob]

Is this a PC SMPS?

If so, you're asking for a LOT of explaination.

Generally, these transformers have multiple inputs (feeds, feedbacks) plus outputs for developing ±12VDC, ±5VDC, 3.3VDC, etc.).

In other words, a pretty complex array of transformer duties. You might (I'm just suggesting) try looking at a somewhat less complicated SMPS (search "Joule Thief" on this ETO site, for instance).

 

[r.raslan]

No.. it is for a medical device. It is Video Printer which could be connected to a medical scanner device that has Video out signal then connected to this printer to thermally print the captured photo.
I should get this device fixed but I can not find any deffictive part.
My main problem is: the SMPS is not functioning. The primary side seems to be working fine as the generated DC voltage is about 300 V DC and I have tested and replaced the MOSFET, Triack, PWM IC, PNP Power transistor and I have tested the rest of the components like diodes and zenrs and power resistor but still not working.
So the last think I can figure is the high frequency transformer. But the problem how can I test it? with Ohm ranger on DMM, I can see the resistance between its coils about 0.5 Ohm (which too low I think?)

Can you help?

 

[cowboybob]

Without a schematic or other circuit diagram, I'm afraid that any advice I gave you would, at best, be a "SWAG" (scientific-wild-ass-guess)... and of little practical use: especially involving a transformer with 16 pins.

How about a Brand name and/or a Model number for the imager? Or any identifying numbers/letters info on the transformer?

 

[r.raslan]

the available number is: 350P5010 1323M

 

[tvtech]

No.. it is for a medical device. It is Video Printer which could be connected to a medical scanner device that has Video out signal then connected to this printer to thermally print the captured photo.
I should get this device fixed but I can not find any deffictive part.
My main problem is: the SMPS is not functioning. The primary side seems to be working fine as the generated DC voltage is about 300 V DC and I have tested and replaced the MOSFET, Triack, PWM IC, PNP Power transistor and I have tested the rest of the components like diodes and zenrs and power resistor but still not working.
So the last think I can figure is the high frequency transformer. But the problem how can I test it? with Ohm ranger on DMM, I can see the resistance between its coils about 0.5 Ohm (which too low I think?)

Can you help?

.

You don't know what you are doing. Changing parts and hoping to get lucky is the wrong approach.

For starters, if you have 300 to 320VDC across your Main Smoothing Cap and no fuses or safety resistors blown......your Primary Side is "Probably" OK. Could be startup issues on the Primary though....Nothing blown is always a good sign.

Sounds like you have Secondary issues and the PSU is protecting itself.

Chopper Transformers rarely fail.

In around 10000 to 20000 TV's now...only around 3 I have ever witnessed to fail. All due to PCB failure ..arcing, dry joints etc. that physically burnt the connections to the Transformer windings. Never the Transformer itself.

I will not elaborate further. Think for yourself.

Fixing SMPS is an Art and needs an understanding of Electronics and LOTS of experience. You might get lucky.....luck does not last long with a SMPS that has not been repaired properly...waay beyond the scope of this post.

Bang = start again . Rebuild. Again. Variac's help though. If people would only listen....

Good Luck

Regards,
tvtech

 

[cowboybob]

Is the device an ultrasonic imager (just guessing)? Since the unit is using a thermal printer, I'd venture that it's also fairly old.

With what you have provided thus far, the chances of finding a schematic are slim and none (unless you way-lay a service tech and steal one...).

What are the symptoms of the printer (please be very specific)? For instance, "Nothing - no panel lights - no nothing", or "Won't print an image", or "won't advance paper", or "won't even print a test page", etc..

As an afterthought, are you sure the imager is sending a signal (picture) to the printer?

 

[r.raslan]

Drea tvtech, thanks for your reply even though it has high tone
I am not an electronics started... but my specialty is medical electronics and not Power electronics!!! So I never been studied about this field and I am trying to educate myself in this field in order to get the thing fixed and not as trials and errors. I appreciate your understanding to my situation and thanks or your help trials!


Dear cowboybob, thank you for your reply. The printer is ultra sonic attached thermal printer and yes it is old one. now, what are the problem symptoms? the printer is not working at all... by testing the power board (SMPS) I found it does not generate voltage at all.

 

[cowboybob]

Please bear with me here...

With only a DMM it's going to be difficult to diagnose your problem. But if that's all we have, well then we'll see what we can do.

So, some more questions:

1. Are the imager and the printer fed power from the same SMPS power supply?
2. If so, is the imager working? If yes, can you tell which part of the SMPS board is feeding power (or would be if it were working) to the printer?
3. If not (i.e., the imager and printer have seperate power supplies), then can you tell if they receive their power from the same source (mains, whatever)?
4. And in the 3. above, are there any obvious fuses? (I ask this only to confirm, not insult)?
5. Lastly, is the printer built-in to the imager unit (I suspect that it is) and does it look like it is a "normal" (brand name) thermal printer adapted to the imager or one that was specifically designed for the imager unit? .

I'm trying to get a picture in my head of the whole unit. Speaking of which, can you provide photos? Especially of the printer connector(s) to the SMPS and the imager.

 

[tvtech]

Drea tvtech, thanks for your reply even though it has high tone
I am not an electronics started... but my specialty is medical electronics and not Power electronics!!! So I never been studied about this field and I am trying to educate myself in this field in order to get the thing fixed and not as trials and errors. I appreciate your understanding to my situation and thanks or your help trials!


Dear cowboybob, thank you for your reply. The printer is ultra sonic attached thermal printer and yes it is old one. now, what are the problem symptoms? the printer is not working at all... by testing the power board (SMPS) I found it does not generate voltage at all.

I am sorry for sounding harsh. And thank you for being such a good person that doe's not take offense.

The environment I work in leaves no time for experimenting with SMPS. You either know them or you don't

Don't = bad.

Seriously.

Regards,
tv tech

 

[r.raslan]

Hey tvtech, do not take it so seriously! I did not felt bad about your reply as I appreciated a lot. Also, I can really understand you about some stupid questions asked by people who are trying to do things beyond their abilities such as an electronic starter wanted to build SMPS and s/he has no clue where to start. Then s/he post in the form help please... aiming someone will do the work for him/her hahaha sounds fool ya?

 

[r.raslan]

cowboybob, thanks for the help and here are the answers:
This Ultra Sonics (US farther in this text) is used for real on time monitoring and diagnostic. Now, the doctor has an option either to follow up on the monitor, or freeze the captured image in order to print it for documentations purposes.
Basically, the printer is a stand alone device that could be attached to the US. It considered as optional peripherals and sold separately. The US and printer are separately connected to the main power (220V/50Hz) so every device has its own power. The only connection between the US and printer is an axial video cable.

For the photos, I have attached Microsoft Word document and Datasheet in PDF format.

Professionals, All your help are highly appreciated!
BR,
Razi

 

[cowboybob]

OK.

For starters, let's look at the power situation of the printer.

NOTE!!: LETHAL VOLTAGES EXIST in the printer, especially in the areas you will be testing. Take extreme caution when performing these tests!!

If you cannot read a schematic or are at all unsure or uncomfortable about performing these tests, STOP and seek professional assistance!

If you are unclear about the locations I desribe below, please submit in focus pictures of the WHOLE PCB and then close-ups of quadrants showing the SMPS chip and surrounding components.

This is a preliminary group of tests for basic power to the SMPS chip. Others may need to be performed.

1. Check which SMPS chip you have, i.e., the M51977P (16 pin)View attachment 69143 orView attachment 69144 (20 pin)

2. Note chip orientation markers.

View attachment 69145

Using schematic above, taken from the Datasheet for the M51977P (check point 2 is in two locations - they are identical): Your particular circuit may vary, especially in the Mains to transformer area!

3. Check for DC values on pins marked 1 (Vcc) and 2 (Gnd).

4. If DC value between 12 and 30VDC, STOP!

(At this point my best guess would be that the SMPS chip, or some other component associated with it, is defective.)

5. If not, check for AC value between 2 and 1AC. If present, the diode to the left of the check point is defective.

If DC values thus far are all very low or zero, continue with 6. below:

Again, NOTE!!: LETHAL VOLTAGES EXIST in the printer, especially in the areas you will be testing. Take extreme caution when performing these tests!!

6. Using schematic above, check for DC values across points 3 and 4 for a DC value in excess of 100VDC. There may be an AC component.

7. If present, check for value across points 4 and 5. If similar to step 6. above, then quite possibly the transformer is defective.

Let us know what you find.

 

[r.raslan]

The DC voltage between point 1 ad 2: Vcc - GND = 14.5 V DC
Please be informed that I have replaced this IC: M51977P (16 pin) with new one and I have got the same results.

 

[cowboybob]

OK. Let's check some more values (If your DMM has a Frequency option, use it. Otherwise, just AC):

(Don't forget: LETHAL VOLTAGES!)

Use the schematic below:

View attachment 69153

Check between points 1, (Gnd) and point 2:

There should be a 500kHz signal somewhere between 700mVAC to 14.5VAC (can't really tell what it will be, but NOT zero).

If so, then check across the points 1 and 3 (across the MOSFET driver, if there is one):

This value should also be about 500kHz at about 50VAC (I''m guessing here, it's the driver voltage for the transformer's input). If it is pure DC (no AC component) the MOSFET is kaput.

 

[r.raslan]

Here are the requested measurements:
Measuring between 1&2: Pin 13 (GND) and Pin 2 (Vout) = 0 Hz & 0.030 V AC & 0.017 V DC
Measuring between 1&3: Pin 13 (GND) and Pin 1 (Collector) = 0Hz & 1.70 V AC & 13.38 V DC

Measurements took place directly on the MOSFET pin with respect to GND:
Gate voltage = 0.015 V DC
Drain voltage = 296 V DC
Source voltage = 0 V DC
Frequency at the Gate: 0 Hz

 

[cowboybob]

OK.

Obviously not oscillating.

These chips were designed to allow a "stand-by" condition, i.e., they can be turned on and off (with mains applied). Either by stopping oscillations (pins 9[ON] and 11[OFF] as well as pin 5 (ON/OFF) which needs to be grounded for the chip to operate, best I can tell.

Again, not knowing for sure which circuit you have, but assuming it's similar to this one:

View attachment 69172

<EDIT 7 Dec 2012, 10:25PM> Just went back to your post #14. For whatever reason, I missed the Word Doc with the pix of the printer PS board. As a result, the next two questions below are unnecessary. I apologize for any misunderstanding. </EDIT>

On the imager (or printer) unit, is there any sort of "enable" switch, button, selection, whatever that must be toggled for the print function? <EDIT> Yes there is.

Do you see any chips that can be identified as Opto-isolators such as the ones in the above circuit? <EDIT> Yes there are.

What value(s) are on pin 5 (ON/OFF terminal), 9 (T-ON) and 11 (T-OFF)?

I know this is tedious, and maybe futile in the end, but nothing ventured, nothing gained...

 

[Mr RB]

...
Measurements took place directly on the MOSFET pin with respect to GND:
Gate voltage = 0.015 V DC
Drain voltage = 296 V DC
Source voltage = 0 V DC
Frequency at the Gate: 0 Hz

Looks like the start resistors or the small electro caps in the primary.

If there are small electros near that FET and opto on the primary side, just replace them, especially any near hot things like heatsinks. 10uF is a particularly bad value.

Look for the "start resistors" these are usually two identical resistors with a yellow third band (270k to 470k range) although sometimes it can be just one resistor. The resistor goes open circuit or very high in ohms. You can just unsolder one leg of each resistor and lift it up to disconnect that leg, then measure the ohms of the resistor.