Comments on: AC Power Adapter Repaired

By: Paris Azis

Paris Azis — Thu, 26 Nov 2015 09:51:25 +0000

In reply to Hermann.

Hi Hermann

You are right about the explanation you expressed (or at least I fully agree with it).
A simple proof about the validity of this opinion as a true one is the fact that when a driver (and of course isolating) transformer is used between the P.W.M I.C and the power output semiconductors in order to trigger them, this IC rarely gets destroyed. Usually only the power semiconductors are found shorted out (along with the main fuse of course and perhaps the relevant resistors in their emitters or sources, if they are used, depending on the type of the semiconductor used).
Furthermore, this is the usual situation related to small SMPSes, especially to those working in “current mode”, like this one of the present repair. In fact these I.Cs rarely escape their instant death when the device they drive fails…

Greetings

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By: Agustin Lalu

Agustin Lalu — Thu, 26 Nov 2015 04:11:59 +0000

Very interesting and lots of information on how to find the right components for subtitute very well done sir thank you very much for sharing Godbless...

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By: Bhupendra Thakur

Bhupendra Thakur — Wed, 25 Nov 2015 14:20:54 +0000

Dear Parsuraman,Good work.Thanks for sharing the information.

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By: reza

reza — Tue, 24 Nov 2015 19:56:15 +0000

hi Parasuraman Subramanian
thank u very much.

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By: Parasuraman S

Parasuraman S — Tue, 24 Nov 2015 05:41:32 +0000

In reply to Peter O.

Thanks for your support. It took just less than 30 minutes to complete the job. After reading and understanding Jestine Yong's SMPS repair book, in which he states that SMPS servicing is an altime challenge for any technician, I love such challenges and spare no effort to understand and rectify the root causes.

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By: Peter O

Peter O — Mon, 23 Nov 2015 23:23:24 +0000

Surprising that so many components had failed.
You persisted & gave yourself time to complete the repair.
Generally I'd suggest that "replace with new" would probably be more economic.
However this is not always easy either, & aquisition delays can be lengthy.
I suspect many like me would like to know how long this repair took?

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By: mabrouk

mabrouk — Mon, 23 Nov 2015 19:19:06 +0000

thanks a lot for sharing this good work

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By: Dennis Breda

Dennis Breda — Mon, 23 Nov 2015 17:53:14 +0000

Thank you for the thorough explanation. I work alone and am isolated from sharing knowledge. This is a great form.

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By: Albert van Bemmelen

Albert van Bemmelen — Mon, 23 Nov 2015 17:49:29 +0000

Hi Parasuraman, well done! It must give a very nice feeling to have repaired such an important Switching Power Adapter. Repairing those new SMPS supplies is great fun! Anyway, the 3842 PWM controller chips can also be tested with the great working little tester that was published a while ago on one of Jestine's articles, or published in his e-book. That is also maybe a bit safer because that one works on a low transformer voltage. I believe it was only 13 V AC. Thanks for your article.

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By: Hermann

Hermann — Mon, 23 Nov 2015 17:11:00 +0000

Interesting read, as always!

From my experience, when the MOSFET shorts its gate with source, it very likely kills the PWM chip, because the full 350+ volts will hit the chip with no chance of survival.

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