Ticking PSU

[R_J]

Re: Ticking PSU

Without knowing what the smps IC is, it could just be in a low power mode since its not under load. I would not worry about it myself.
It can't be from the actual switch circuit or anything on the secondary as the power supply runs at around 30-50 plus kilohertz.

[madan1]

Re: Ticking PSU

There is no IC on the board. I'm not familiar with PSU designs and definitely hate working with high voltages, but I guess there is some kind of an oscillation occurring in the highV part which is making it to switch.

[R_J]

Re: Ticking PSU

I guess it just uses a fet and few components to make it switch, I've seen similar power supplies in dvd & older vcr's

[madan1]

Re: Ticking PSU

I guess it just uses a fet and few components to make it switch, I've seen similar power supplies in dvd & older vcr's

this is what I was able to get as a diagram from the actual board


( see previous page, last post for details )

[R_J]

Re: Ticking PSU

That could explain the waveform, most smps that use a dedicated ic employ some kind of zero cross switching. without it the power supply switches the primary anplace in the sign wave.

[momaka]

Re: Ticking PSU

this is what I was able to get as a diagram from the actual board

https://www.badcaps.net/forum/attach...2&d=1543774648
( see previous page, last post for details )

Your diagram appears correct for a 2-transistor circuit, more or less.

Z103 is likely used as protection on the Gate of the 2SK3567 MOSFET.

Did you check C107 out of circuit, by the way? It is connected between Drain and Source of the 2SK3567 MOSFET. So if you got that reading in circuit, that could indicate the MOSFET is bad instead.

These 2-transistor designs don't like it at all when any parts go bad. Thus, if you ever need to fix one, know that you have to check everything.

That said, in case you are interested, here are some 2-transistor circuit diagrams I drew of some ATX PSUs in my collection:

One from a PowMax ATX PSU...
https://www.badcaps.net/forum/attach...0&d=1451693563
This one is probably the closest to what you have in your power adapter:

And below are some CWT (Channel Well Tech.) designs... with different revisions from CWT throughout the years, hence the variation. They seem a bit more elaborate, but they still work the same.
https://www.badcaps.net/forum/attach...4&d=1407035562
https://www.badcaps.net/forum/attach...1&d=1406952554
https://www.badcaps.net/forum/attach...9&d=1443215464

[madan1]

Re: Ticking PSU

All components from the above diagram were tested out of the board on a "M328 transistor tester" and DMM.
Both transistors are recognized properly. C107 and Z103 are read as "unrecognized"/no capacitance and shorted.

" These 2-transistor designs don't like it at all when any parts go bad. Thus, if you ever need to fix one, know that you have to check everything." - this is what bugs me most - if I will ever be able to fix the PSU without knowing what the z103 is and what should be the values of the rest of the components.
Thank you for the diagrams!

p.s. I checked again the bad diode and this time was able to read 27B on it ( thanks to the macro camera ).

[Per Hansson]

Re: Ticking PSU

The Zener diode might be ok, the transistor tester can only output a low voltage, because it's powered by a 9v battery.
Try using a bench power supply to test it, plenty of tutorials available on Youtube for it...
E.g this one: https://www.youtube.com/watch?v=5OcoF0nkgng

P.S: You don't need to set the voltage like he does, just give it 30v and if the Zener works it will show the voltage.
Obviously the current needs to be limited else the magic smoke will escape.

[momaka]

Re: Ticking PSU

this is what bugs me most - if I will ever be able to fix the PSU without knowing what the z103 is and what should be the values of the rest of the components.
...
p.s. I checked again the bad diode and this time was able to read 27B on it ( thanks to the macro camera ).

If I am not mistaken, that part number suggests a 25V Zener diode... which more or less makes sense. In this particular case, the 2SK3567 MOSFET has a absolute maximum Gate-Source voltage rating of 30V. And we can see that this MOSFET's Source is connected to primary-side ground and its Gate is positively biased from the +170V/340V DC bus (the positive leg of the primary cap) though resistor R101. Therefore, to make sure the MOSFET doesn't get damaged, ZD103 must have a rating of less than 30V. 25V is reasonable, I'd say. But it would probably work with a lower-rated Zener diode too, in case you can't find a 25V Zener exactly.

Also, I just noticed, but are you sure ZD102 is drawn correctly on your diagram? If it is, it would seem to limit the Gate voltage to about 0.7V, which doesn't make much sense.

As for C107... most likely, that should be a few hundred picoFarads (pF) up to maybe 1 or 2 nanoFarads (nF). I don't see any SMD components on your PSU, so unless the cap is blown into bits and pieces, you should be able to read the capacitance off of its case.

[madan1]

Re: Ticking PSU

Thank you for all replies!
I installed new ZD 27V and C107 (22pF ) and got back the voltages on the secondary side.
Then put the correct bus capacitor ( 47/400 ) and now I do not have any visible ripple on my "scope" ( I'll attach images soon ).

[madan1]

Re: Ticking PSU

Here are the waveforms without load ( for 12V and 5V ).
With load the fluctuation is about 15-20mv and frequency of ~25khz and ~130khz for the two V rails ( no clear sines though and lots of noise ).
Fortunately, the HDD seems to be happy with that. The mainboard also manages to filter the supply and for now everything works fine.

P.S. - no ticking sound at all!
Btw, when the "ticking" was present, the NAS was running in emergency mode with almost none functionality and refused to re-build its software.

[momaka]

Re: Ticking PSU

Great to hear you got it running again.

Yes, with self-oscillating discontinuous flyback designs, you won't see a "set" frequency nor any particular waveforms (especially sinewaves). They kind of "run wild", so to speak.

But what I like about 2-transistor designs is that you can always find parts for them, as they don't require any special ICs. On the downside, 2T designs lack protections... but that's the trade-off.