Air Condition PCB - Burned SMD Resistor Values

[sdancer75]

Hi,

I am trying to repair an Air Condition PCB that burned a PWM (NCP1200), an N-channel MOSFET (IRFUC20 MOSFET N-CH 600V 2A) and two SMD resistors. Take a look of them in the attached photos.

So my question is :

1. Do does exist any schematic for this PCB?
2. In NCP1200 PWM datasheet for some projects suggests a >4.7KOhm resistor for pin8. Should I replace the burned SMD with that value? What values do you suggest?

[wasyoungonce]

Appears to have a SMD resistor pin 5 to gate of the FET although it looks to be a divider to gnd the middle going to the FET gate.

Its hard to tell from the pic.   I looked a ta dew schematics on google of the control cctry IC and some do have a gate resistor but none appearing to have a divider network.   The PDF does mention legacy designs AND8023 and I did see a schematic using AND8076 using said divider to gnd...amongst other changes....all very similar to yur IC.

https://www.google.com/imgres?imgurl=https%3A%2F%2Fstatic5.arrow.com%2Fpdfs%2F2012%2F2%2F5%2F4%2F58%2F2%2F288%2Fons_%2Fmanual%2Fand8076-d_fig.13.jpg&imgrefurl=https%3A%2F%2Fwww.arrow.com%2Fen%2Freference-designs%2F70w-165v-ac-to-dc-single-output-power-supply-for-atx-power-supply%2F8b0acf4b07602981dc693b901d5e1d47&docid=Z_Kelok3GMVplM&tbnid=I0z4bB4ZfCK4GM%3A&vet=10ahUKEwiYwoLt34bjAhUKWCsKHZipAMcQMwhSKBAwEA..i&w=1074&h=609&client=firefox-b-d&bih=886&biw=1680&q=NCP1200%20air%20conditioner&ved=0ahUKEwiYwoLt34bjAhUKWCsKHZipAMcQMwhSKBAwEA&iact=mrc&uact=8

FWIW

[sdancer75]

Hi

I suppose you refer to resistors R9 and R10 right (and maybe to R4)?

[wasyoungonce]

R9 & 7 in the sch looks like R75 & whatever in your pic.  I wonder if one is actually a ferrite bead to the FET gate?     It’s hard to tell. 

Also as usual change all main electro caps.

[sdancer75]

Hmmm.... Its a risk I think, I will buy a used one and then I will try to fix this......