What do you say about that? As you see changing diodes is an easy task. I just wonder about what starcruser said  for the filters.

Hi Jeg. I haven't analyzed switch mode power supplies much at all, so assume I could possibly be mistaken
on some of this.

It looks like the section I have enclosed in a white box is where some input filtering components would be, but these
are not installed, so that makes it easy.

As you likely know, the FWBR diodes enclosed in the yellow box should be replaced with fast power diodes if they
are not fast diodes. If you can read the part number on one of their sides, you can check before unsoldering.

What is the part number for the part which I enclosed in the red square? I am not certain what it is.
Can you see any markings on the side of that part?

Overall it looks like you may be able to just put in fast power diodes and you may be set for frequencies such as
27 kHz or in that area. I can't say for certain there won't be other issues as I haven't tried this, but just commenting
on what I think after taking a quick look. There doesn't appear to be much in the way of input filtering that
I noticed, but maybe someone with more experience with switch mode power supplies can add further input...
All the best...

P.S.
What is the voltage rating on the electrolytic filter caps right after the FWBR diodes?
You may well have to add a bit of your own filtering on the AC output of your device if the
signal has any high voltage spikes or whatever on it, before going into the input of the power supply.
You will also want to make sure the voltage of the input waveform is reasonably close to it's rated value.

Guys thanks a lot for your help.

Void, this component at the input side is an NTC like the one akula uses between ground and the three turns yoke output circuit.
Starcruser, i feel you are absolute right about those electrolytics. They worry me also. I will try to unscrew the pcb so to draw a quick component connection to see what happens. I ll post the result.

P.S.
What is the voltage rating on the electrolytic filter caps right after the FWBR diodes?

You may well have to add a bit of your own filtering on the AC output of your device

I will check it again later on cause i am not home, but i think 370uF per cap

I have a bunch of varistors at 220V, thanks for notifying this!!

Maybe someone can explain what the NTC (thermistor?) is there for? Anyone know? Spike protection?

The NTC acts as a thermal fuse in series with the mains supply. It is designed to take a surge on connection to the mains as the big cap (400v rated after the FWBR) charges up to around 375V. Don't alter the cap size as its designed to suit the current rating of the SMPS.

So long as the input voltage is not higher than the mains and is not spiking badly when scoped, then this should be fine. Most SMPS PSU's have quite a wide input voltage range. The input voltage is very unlikely to rise to the specified max when loaded by the device. C36,37,38 & L13 is the filter.

Thanks Hoppy. So it is in series in the neutral line? It adds resistance and reduces current surge
until it warms up, and then has negligible resistance, or how does it work exactly?

Regarding the voltage on the electrolytics, 240Vrms x 1.414 = 340V
Would that not be the voltage on the filter caps?
Either way, I would hope the caps are rated at 450V if the operating voltage is that close,
but maybe they pinch every penny.
All the best...

See:  http://www.digikey.co.uk/Web%20Export/Supplier%20Content/api-technologies-1171/pdf/api-ntc-engineering-notes.pdf?redirected=1

Most are 400V rated. This cap works very hard and must be a 105 degree working device with low ESR.

For Russian speakers, I think Ruslan has commented on realstrannik that he would be willing
to use some group chat program to hold a group chat and answer people's questions.
Don't know if that will happen, but Ruslan suggested it recently, from what I could understand
using Google Translate anyway.  Nick, do you speak some Russian?

And this small board