bn44-00604F No Secondary Power

[R_J]

Re: bn44-00604F No Secondary Power

I find that in this board the R sense is connected to ground side and if it gets short, worst that can happen is it gives B- to the pin, which is ground in this case. Thanks for explaining transformer ckt.

Then saw the power resistor right next to the MOSFET was bad and did not show any value. Bypassed it as well considering it was providing GND to the source of MOSFET

You don't understand, When the mosfet shorted the source resistor went OPEN. Now ALL the 300 volts will appear at the mosfet source. R101 is connected between the mosfet SOURCE and the ic OCP pin. If you think that ic's ocp input handled that, then there is no convincing you otherwise.

[nomoresonys]

Re: bn44-00604F No Secondary Power

How is that IC $30, some crazy shipping costs??

[afnan]

Re: bn44-00604F No Secondary Power

Without the exact diagram it is difficult to say what is wrong other than the capacitor on the VCC pin should initially charge to 15V and this is supplied via the voltage at the ST pin.
If there is no kick start voltage across the capacitor connected to the VCC pin then either there's a problem with the path supplying the voltage to the ST pin, the VCC capacitor is faulty or the IC itself is faulty.
You mention earlier that VCC - GND = 170 ohms which does seem to be low. Have you checked the components that feed back from the transformer to VCC.

Would be interested in what others think since it's all guesswork on my part.

Please find attached picture of the actual ST and VCC related ckt

[afnan]

Re: bn44-00604F No Secondary Power

You don't understand, When the mosfet shorted the source resistor went OPEN. Now ALL the 300 volts will appear at the mosfet source. R101 is connected between the mosfet SOURCE and the ic OCP pin. If you think that ic's ocp input handled that, then there is no convincing you otherwise.

I am sorry if any of my comments didn't make sense. I did not factor in what will happen once the MOSFET shorts out.That schematic was for a typical SSC3S111 working. I have attached above the actual one traced from the board. You are correct.

[afnan]

Re: bn44-00604F No Secondary Power

How is that IC $30, some crazy shipping costs??

Yes, shipping.

[R_J]

Re: bn44-00604F No Secondary Power

$3.56 for 5, free shipping
https://www.ebay.com/itm/5pcs-35111-...1&isGTR=1#shId

[jetadm123]

Re: bn44-00604F No Secondary Power

$30! Just where exactly is it being shipped from? As R_J mentioned, this part is readily available through eBay and also aliexpress. Full part number is SSC3S111. Wouldn't hurt to also change the small startup cap tied to the VCC pin.

[afnan]

Re: bn44-00604F No Secondary Power

$30! Just where exactly is it being shipped from? As R_J mentioned, this part is readily available through eBay and also aliexpress. Full part number is SSC3S111. Wouldn't hurt to also change the small startup cap tied to the VCC pin.

Thanks. Purchased.

[afnan]

Re: bn44-00604F No Secondary Power

$3.56 for 5, free shipping
https://www.ebay.com/itm/5pcs-35111-...1&isGTR=1#shId

I was able to find 0.33 Ohm resistor. The resistor used previously was 0.30 Ohm. Would it be alright if I use this?

[ik3umt]

Re: bn44-00604F No Secondary Power

I'm attempting to repair similar schematics Samsung Power Supply (BN44-00750A) , dead with fuse OK
15NM65M Mosfet shorted, replaced with 16N65M (looks very similar)
R107, R108, R113 interrupted , replaced.
I have replaced also 3S111 with same model (is 3S111 similar to 1S311 ??? )
Checked all surrounding components except capacitors...

Powered up, immediately blown fuse and shorted mosfet !!!

Any hints ?

Thanks