Comments on: PFC Controlled Power Supply Unit Repair

By: Albert van Bemmelen

Albert van Bemmelen — Fri, 21 Dec 2018 11:25:31 +0000

In reply to Oliver.

I replaced it of course! Else the power supply would still not work.

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By: Oliver

Oliver — Sun, 22 Jul 2018 10:02:53 +0000

Sir did you just remove the resistor and did not replace it?

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By: Albert van Bemmelen

Albert van Bemmelen — Sat, 14 May 2016 15:56:53 +0000

In reply to Humberto.

Question Humberto, you haven't got fortuitously such an identical
BESTEC HP laying around at home? I am trying to repair mine and
found a big (Fairchild/Samsung) SSH7N90A n-channel 900V 7A RDSon 1.8
Ohm 240 Watt shorted between Drain and Source Mosfet. And a bad D3
Diode with a bad R105 on the solder Board side. It would be nice to
know what value R105 or D3 will be.

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By: Yogesh Panchal

Yogesh Panchal — Fri, 13 May 2016 07:25:30 +0000

Albert,

Thanks for sharing your experience

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By: Albert van Bemmelen

Albert van Bemmelen — Wed, 11 May 2016 08:20:51 +0000

In reply to Paris Azis.

Thanks Paris. As said you gave me the solution were to look. And it is
almost unthinkable that it again was only one single cheap component that
was the cause. I missed that single 4.7 Ohm Resistor thinking it was just
a high Ohmic value (about 1 MOhm or higher). Because it was hidden in a
black shrink socket I couldn't see its actual value. But after your tip
and drawing the Schematic it was solved in no time!

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By: Albert van Bemmelen

Albert van Bemmelen — Wed, 11 May 2016 08:11:22 +0000

In reply to Humberto.

Hi Humberto.
It is almost unbelievable that it is often only one component
that prevents the complete SMPS unit from working. Which is also the
case in the ATX 410 Watt Power Supply repair that soon will follow.
PS: After we have written each other a couple of times, I recently also
added Paris to my Email contacts. It is very nice that, thanks to
Jestine, whatever distances we live apart, we always can write with one
another. Without even leaving our homes. The electronic future brings
nice surprises.

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By: Paris Azis

Paris Azis — Tue, 10 May 2016 18:44:14 +0000

Well done dear Albert! I am glad you finally fixed it.

Best Regards

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By: Humberto

Humberto — Tue, 10 May 2016 18:07:25 +0000

Hi Albert, you have done a deep schematic, good explanations (as usual), good photos and at the end:an excellent job. By the way, many readers have liked your article, so Congratulations. Albert.

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By: Humberto

Humberto — Tue, 10 May 2016 17:52:00 +0000

In reply to Albert van Bemmelen.

HP uses BESTEC SMPS in many PCs they manufacture.

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By: Albert van Bemmelen

Albert van Bemmelen — Tue, 10 May 2016 13:31:11 +0000

In reply to paul.

Hi Paul, if you look at the quick made hand drawing I did, you´ll see a
resistor marked R910 (notice also the black pointing arrow) it is coming
from the plus pole from the rectified Voltage on the Big Buffer E-Cap.
And going to Transformer pin 1 that is also attached to the standby
circuit of the TNY277. R910 was a completely open resistor. Why the about
DC 400 Volt couldn´t reach the pin 1-3 Transformer coil. And why the
complete Power unit was defect. Without that coil Voltage there won´t be
any Voltage on pin 4 of the TNY277 either coming from pin 3 of the
Transformer coil, and the TNY277 will go in Standby mode or be inactif.
If you want to know how it works you better study this Datasheet: http://www.elenota.pl/datasheet-pdf/162047/Power-Integrations/TNY277
That is all to know I think.

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