ZyXel NAS - an AC brick was connected

[Behemot]

A guy connected 16V AC brick instead of 12V DC brick.

There are some two tiny components of package similar to SOP, just have like 2x4 mm. Probably protection devices for this purpose, they do not have continuity with voltage applied. One is labeled RADRRR and has 5 legs. The other one is 6-leg 564Z and this should probably pass the voltage as there is +12 V coming in and output should go through filtration capacitor into AX3108 PWM step-down controller, but has 0,13 V on output (thus 0,13 V on capacitor and PWM). Any idea what this is?

[kaboom]

Re: ZyXel NAS - an AC brick was connected

Any pictures?

[Behemot]

Re: ZyXel NAS - an AC brick was connected

Yeah I've been dead, barely able to write that text, just been woken up (in the middle of sleep cycle so I'll be like idiot the whole day again), let me get a shower and stuff and than I'll take pics…

[Behemot]

Re: ZyXel NAS - an AC brick was connected

Here are the bad boys with 564Z on the left.

[budm]

Re: ZyXel NAS - an AC brick was connected

It looks like that IC U10 feeds the fuse F1. Did the fuse blow also? Pictures of the whole board top and bottom?

[Behemot]

Re: ZyXel NAS - an AC brick was connected

It's the other way around: jack - coil - fuse - ICs - cap+regulator. Fuse is OK, just those ICs (and probably especially the 564Z) don't pass the voltage.

[kaboom]

Re: ZyXel NAS - an AC brick was connected

If you can power this from a current limited 12V supply and are reasonably sure these connections/subs with diodes make sense, try what I've edited in...

You can use 1N400x diodes.

I almost think those parts are custom marked. Either that or there's an SMT number cross that I'm not aware of.

[Behemot]

Re: ZyXel NAS - an AC brick was connected

Yeah I though about just using diodes as well. The AX3108 can eat voltage up to 20 V so using even 12 V AC would be just OK…I can stick in anything, I have plenty diodes removed from this and that, all have at least 30V rating.

Current will be limited with power brick which can only handle 1,5 A

[Behemot]

Re: ZyXel NAS - an AC brick was connected

It works with one BYV28-200, will try to squeeze the other one in but it will be tricky. Even the first one was hell to solder onto those tiny pads…

ADD// Done. I must be getting better

[budm]

Re: ZyXel NAS - an AC brick was connected

on post 7 notes: It looks to me that U10 Diode is hooked up as the crow bar protection in case the 12VDC with wrong polarity or if AC is applied to the input is hooked up top the unit.

[Behemot]

Re: ZyXel NAS - an AC brick was connected

I don't think so. If you connect wrong polarity than it would behave like -12 V on ground and 0 on voltage side, which…does not matter, right? Anyway, if you connected it other way around, it would be directly shorted to ground with positive voltage applied.

[budm]

Re: ZyXel NAS - an AC brick was connected

As you can see the Anode is connected to ground plain, the Cathode is hook up to the + (through the fuse, the inductor, the input jack), So if you hook up AC adapter to the jack, the diode will conduct in both direction of the AC cycle (you are basically put the diode in parallel with the output winding of the transformer.
If you feed the unit to the DC with correct polarity, the diode will not conduct since it will be in reverse bias mode, if the polarity is reverse, the diode will bias on and conduct and basically crowbar the circuit to 0.6V max voltage, that is how diode crowbar circuit function. It is one of the cheapest way for protection against reverse polarity or AC input.
http://www.eevblog.com/forum/beginne...ch=20420;image

[Behemot]

Re: ZyXel NAS - an AC brick was connected

Oh yeah it makes sense, I've been thinking scenario of negative voltage applied. With positive-reversed it will just short making the supply go into protection (or burn in the case of transformer brick).

[ben7]

Re: ZyXel NAS - an AC brick was connected

U9 seems odd, it has 4 legs connected together, it could be a FET. I hate it when PCB designers mark semiconductors with 'U', it can be very hard to distinguish a diode and/or transistor from an IC.