Chicken or the egg ?

More likely one transformer and 2 chokes, unless you have a specific reason to say otherwise.

Graham

reason to

Why would chokes bridge the "no man's land" isolation strip between HV and LV areas ?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

No, probably transformers instead of opto-isolators (on the feedback and drive).

Personally, I wouldn't even attempt to do any serious troubleshooting on a supply of this type unless there was no inexpensive replacement. I would check the obvious - ESR of e-caps, open high value startup resistors, and such. But beyond that, these tend to be infinite frustration sources. :( :)

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and

is

in the

I don't mind challenges unless someone wants a turnaround repair, which this is not. Its just practise for some future dedicated complex supply that has no generic replacement. I can see the one large and two small HF transformers tied up with the above process but I wonder what the 4 pin opto device is for, perhaps an overall on/off killer: when the controller flag is high it locks out the main HV oscillator from making any blips.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

On Thu, 4 Oct 2007 09:32:41 +0100, "N Cook" put finger to keyboard and composed:

If it's a typical ATX PSU, then one transformer is part of the +5VSB supply, a second drives the oscillator/chopper, and the third supplies the secondaries. The optoisolator may provide voltage feedback for the

+5VSB rail, or it may be part of a protection circuit that shuts down the oscillator.

See

Otherwise, if you have an AT PSU, then AFAIK the PWM controller on the secondary side gets its supply rail from the very first "kick" of the main oscillator and then "bootstraps" itself into regulation.

- Franc Zabkar

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or

the

main

rails.

pulses

under-voltage

any

Didn't get around to powering from 12V dc but did trace a bit of the tracks. The opto would seem to link, DC fashion, from the 3.3V rail back to the feedback pin of the low power startup IC to shut that one down. This IC, with the reservoir caps, will keep the main smps IC running for 10 seconds after removing the mains supply (in the present unfunctional as a ps state)

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Could be, since the transformers can't provide DC coupling.

The problem is that with no schematic or service manual, there can be so many dead ends and confusion that the experience IMO may not transfer to other areas. It's not clear that the knowledge gained is worth the hair lost. :)

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