Comments on: About Conceptronic 90W Power Supply (Part 2)

By: Albert

Albert — Sat, 16 May 2015 08:57:32 +0000

In reply to Albert.

For anyone that wants to know more about SMPS.... just found a very usefull Guide on Switching Power Supplies. Only 73 pages and very concise from ON semiconductors !

And Free. See: http://www.onsemi.com/pub_link/Collateral/SMPSRM-D.PDF

Albert.

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By: Albert

Albert — Sat, 16 May 2015 08:35:55 +0000

In reply to Paris Azis.

Paris, thank you for mentioning the Motorola book and your usefull advise. I sadly haven't got the book. So I haven't read it either. I take it that the Gap part you're mentioning is only applicable to Flyback transformers in TV's and sorts? And in this case the defect PSU transformer isn't intended to create High Voltage output. So I guess in this case there is no Gap construction in this Universal Conceptronic 90 Watt PSU? I hope to find the book you mentioned to be able to understand what the Gap part is about. Thanks for this information.
Cheers!
Albert.

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By: Yogesh Panchal

Yogesh Panchal — Thu, 14 May 2015 06:55:28 +0000

Good article thanks for sharing.

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By: Paris Azis

Paris Azis — Mon, 11 May 2015 19:08:51 +0000

Hi Albert,

Nice job no matter the result. Knowledge has always a price. It was never for free.

Regards

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By: Paris Azis

Paris Azis — Mon, 11 May 2015 19:03:25 +0000

In reply to Bill Eitner.

Hi Bill,

Nice and encouraging your comment. I fully agree, except for the transformer rewinding advice. Here is why (Motorola,Linear/Switchmode Voltage Regulator Manual,1983, page 11-1).
...It takes quite a bit of time to develop a "feel" for this craft and be able to use both experience and intuition to find solutions to second and third order problems...
And what's more:
...For flyback designs, a gap is necessary...and a test circuit is needed to evaluate the effect of the gap...
If this task is scary for design engineers, is not possible for repairs technicians to succeed with rewindings I humbly think.

Regards

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By: Humberto

Humberto — Mon, 11 May 2015 13:16:23 +0000

Albert, good explanations very scientific. Congratulations.

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By: Albert

Albert — Sun, 10 May 2015 13:56:04 +0000

In reply to Anthony.

Thanks Anthony, Nice of you to say but I do hope to present a better ending repair article next time. Also because of the a bit disappointing result. The more we learn the less a gamble it is. But it must be as they say in English speaking countries: No pain, no gain. Or the he who never tries, never wins stuff.
Bye bye.
Albert.

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By: Anthony

Anthony — Sat, 09 May 2015 20:40:16 +0000

Thank you Albert for taking the time to share the very valuable information from this article with us. Even though it
wasn't the desired outcome the experience has enriched yours and everyone else's knowledge on this blog !
We have all gained from this electronic repair article and that can never be a waste of time.

Thanks again !

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By: Albert

Albert — Sat, 09 May 2015 07:30:47 +0000

Hi Bill, thank you for your possible new repair solution but I don't think I even know how to just open a transformer core without destroying it.
It probably is a lot easier then to dismantle the 50/60 transformer types, which are quite heavy laminated iron type cores. To reduce any unwanted flux or something it was for. And I read somewhere in the past that a guy knew how to dissolve these cores to be able to open them in some kind of chemicle solution but I forgot what he used. And it seems to be a very uncertain way to repair these. Sure these coils are no Tesla type of coils which are a very precise made type of coils. But aren't these PSU transformers not also made on precise automated winding machines?
If I could see someones report with photo's on such a project on how to repair these transformers, I probably knew what I was up against?
For now I won't go this far yet.
Cheers,
Albert.

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By: Bill Eitner

Bill Eitner — Fri, 08 May 2015 18:54:12 +0000

It's somewhat impractical, but the transformer can be rewound.
Anyone who claims to be an electronics tech should have repaired a transformer or coil via rewinding at least once. That's the advantage coils/transformers have over other components; they can be repaired.

It's like a right of passage and is common in antique radio repair.

Old vacuum tube amplifier stages are transformer coupled.
The DC plate voltage goes through a transformer primary winding.

As we all know, tubes are controlled the opposite of transistors.
Grid voltage turns off a tube, whereas base/gate voltage turns on a transistor.
Lose the base/gate voltage the transistor turns off (no damage).
Lose the grid voltage the tube runs full on eventually destroying the tube and often overheating/burning/damaging the transformer.

When you can't find a replacement transformer the only option is to rewind the old one. Enameled wire of the right size is all it takes.
Although not really recommended, in a pinch the bad spot can be spliced depending on the level of damage. Sometimes the failure is just a break at a weak point. What you can get away with depends on the condition of the enamel coating the wire and the design of the device you're working on. For example, with the common flyback style SMPS the transformer turns ratio isn't critical, so the removal of a bad spot or even a short length probably won't effect performance.

So, there you have it.
Albert, if you want to become even more knowledge/experience rich, you still have an option that can result in a complete repair.
Good Luck.

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