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Old 19th April 2015, 08:25 PM   #1
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Unhappy SMPS failure. IR21531. Please help.

Hi guys,

My friend give me his broken mark bass amp. I checked, 220V fuse and mosfets are blown.

All other parts are fine. I changed mosfets irfp460, power on the amp and fuse blowned again.

There are a driver ic on circuit. But numbers erased by manifacturer. Could i replace it with ir21531? If no, what type of driver can i use? Circuit at attachment file.

Please help me. Thanks.

Okan.
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File Type: jpg smps.jpg (130.0 KB, 352 views)
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Old 19th April 2015, 09:43 PM   #2
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The mosfets often take the driver IC with them.
I had this happen a few times on my early SMPS designs.

I can only guess you need to go through each 8 pin SMPS IC and see if any fit sensibly with the other components.
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Old 19th April 2015, 10:47 PM   #3
nec3 is offline nec3  Turkey
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It is highly possible to be IR21531. An oscilloscope is very useful when repairing SMPS.

I am not sure you follow these so i write:

-Connect a 60-100 W incandescent lamp in series with the mains line.
-Remove both IRFP460s and the output load by simly removing fuses if any, or output rectifier diodes at the DC output line.
-Check 12-15V DC Vcc voltage at Pin:1 of IC.
-Check the square wave amplitude and frequency at pin: 5 and 7 of IC. Must be 0-Vcc Volts, and you can find frequency that it should be from the page 3 > http://www.irf.com/product-info/data...ta/ir21531.pdf

-Everything is good, replace Mosfets, rectifier diodes and check output voltage.
-Output voltage is good, remove lamp and check again.

-Always follow this order when repairing SMPS, you will have less blows.


Click the image to open in full size.

Last edited by nec3; 19th April 2015 at 10:57 PM.
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Old 20th April 2015, 06:45 AM   #4
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Thank you.

I have a tectronix 2445b 150 MHz scope. I didn't repair a spms with driver ic before.

In my other smps repairs, there are only blown mosfets and diodes. Check, change and go, it was simple. But now, i am learning new things. Thank you.

I check the datasheet again. I have Rt:18K and read 400pF on smd Ct capacitor. So, i must read a ~16 kHZ square wave. Am i right?

Lamp is a good idea, i am going to try it tomorrow. Today i will buy some irfp460s and driver ics from my component supplier, for blown again possiblity.

Thank you so much again, when i try, i will tell the results.
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Old 20th April 2015, 03:15 PM   #5
nec3 is offline nec3  Turkey
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Quote:
Originally Posted by yamahapower View Post
Thank you.

I have a tectronix 2445b 150 MHz scope. I didn't repair a spms with driver ic before.

In my other smps repairs, there are only blown mosfets and diodes. Check, change and go, it was simple. But now, i am learning new things. Thank you.

I check the datasheet again. I have Rt:18K and read 400pF on smd Ct capacitor. So, i must read a ~16 kHZ square wave. Am i right?

Lamp is a good idea, i am going to try it tomorrow. Today i will buy some irfp460s and driver ics from my component supplier, for blown again possiblity.

Thank you so much again, when i try, i will tell the results.
Looking at the chart given in the data sheet corresponding to 18K-400P, switching frequency must be around 100 KHz.
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Old 15th May 2015, 08:30 AM   #6
pinyoro is offline pinyoro  United Kingdom
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I know this is a late reply but I do not see any mention of use of an isolation transformer when connecting an oscilloscope to a smps circuit.
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Old 15th May 2015, 11:58 PM   #7
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Quote:
Originally Posted by pinyoro View Post
I know this is a late reply but I do not see any mention of use of an isolation transformer when connecting an oscilloscope to a smps circuit.
Thanks pinyoro, i know it. Also user nec3 warned me by pm.

But i didn't fix it yet.

Click the image to open in full size.

This is my schematic. I renewed mosfets and power on circuit after cut the red lines. No fuse blowing. Everything looks fine but when i measure A,B and C test points, readings are huge.

I measured between ground and this points.
A: 249V AC
B: 247V AC
C: -9V AC (when my multimeter set to 750V AC)
-126.7 V AC (when my multimeter set to 200V AC)

I don't have a Fluke, but mine is good, too.

Are these readings interesting? Too high? There are 63V caps, if i connect red lines, they can be blow up.

What's going wrong? Is this transformer failure?

Thanks all for your help.
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Old 16th May 2015, 03:48 AM   #8
yu3ma is offline yu3ma  Serbia
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Can You post some oscillograms from point A, B, C and from pin 5 of IR2153D?

Next, you probably need some bleeder resistors at the output. Put some value to get about 1W of power from PSU.

Regarding measurements with multimeters, forget that for AC measurements on SMPS, use only oscilloscope.
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Old 10th November 2015, 04:18 PM   #9
nafo is offline nafo  United States
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Thanks for schematics pinyoro
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