EV ZxA1 PSU repair

[totoxraymond]

Hi everyone!

So, i have this very nice powered speaker which is blowing fuses.

I replaced both MOSFET on the primary side of the PSU because they were basically dead shorts.

Now, it keeps blowing fuses, and i just noticed this little resistor in the switching control section looks a little bit too dark (r13).

I'm not familiar with SMD, so i'm asking here to make sure i order the right part. (UPS already came twice for this repair).

It's hard to read but i think i can read "180" on the resistor, so could be 18 Ohms?

What is that size? my bad calipers tell me something like 3mm x 2.54mm. My guess would be 1210?

Any opinion on that?

Do you think another component might have gone too?

Thanks!

Thomas

 

[Khron]

What's that resistor connected to?

Odds are it's a(nother) victim of the actual fault, and that whatever replacement you install will get toasted too.

What chip is that 8-legged one there? Photo's too blurry to make out anything.

 

[totoxraymond]

Thanks for your answer,

Sorry, my phone can't make a better picture.

On the ic i can read "IR2131S". Which is a "self oscillating half-bridge driver" so it makes sense to find it here.

Resistor is connected to the gate drain of one mosfet through adjacent cap on one end and to the source of the mosfet / rectifier output / reservoir cap / pin 4 of the driver (COM) on the other end.

Edit: i checked again this morning, resitor and cap are between Drain/source.

 

[totoxraymond]

Hi,

I've drawn the primary side of the schematic, hopefully it makes sense.



I have a feeling that the Full-bridge rectifier is down too.

I measured it in circuit and two diodes measure as dead shorts. (between live and + and between Neutral and -)

 

[Khron]

How long did you measure those diodes for?

Keep in mind those two 1000uF caps (470uF total, in series) will take "a while" to charge up from the ~1mA your meter probably provides on the diode range.

Or do they seem shorted also in the other direction?

You'll probably want to replace the IR2131 as well - for a couple bucks, it's likely not worth the trouble / risk of installing and toasting another pair of MOSFETs.