Identifying burned SMD resistors

[Morsus]

Hello folks, respect to everyone.
I got a electric bicycle charger which got wet and died. After opening it I found some SMD resistors burned out. Here are the pictures. I want to replace these but I can't figure out what its written on them. My guess is "123" (this should be 12kOhms right?) but i'm not sure. I'm still not sure where can I find the exact new ones but if I don't is it much of a problem if I replace them with ones with similar values?
Thank you.

[budm]

Re: Identifying burned SMD resistors

Looking at the board, those 4 resistors connected in parallel to form low resistance value which is connected to the Source pin and used for current sensing of that 3-pin Power MOSFET that drives the primary side of the power transformer. What is the resistance reading are you getting right now? To burn high resistance resistors, the applied Voltage has to be very high.
So you better check and find out if the RESISTANCE between the S and D pin of the MOSFET is showing low resistance reading or not.
We also need the pictures of the bottom side of the board so we can get the P/N of the SMPS IC that drives the GATE of that MOSFET and verify that if I am correct about the circuit.

[stj]

Re: Identifying burned SMD resistors

looks like 10k
so should meter 2k5

[Morsus]

Re: Identifying burned SMD resistors

What is the resistance reading are you getting right now?

I just checked and I get 0 resistance between any of 3 MOSFET pins aka short circuit. Could it be that the MOSFET is blown too?
The charger was probably on rain or something like that so it shorted out or similar.
Here are the pictures.

[gabiz_ro]

Re: Identifying burned SMD resistors

Looks more like 1R3.
Since is on current sensing,must be lower ohm values.
Not all three may be the same value.I see on few devices 2-3 low and one higher value.Reason may be to obtain some unavailable value resulted from design.

[budm]

Re: Identifying burned SMD resistors

I just checked and I get 0 resistance between any of 3 MOSFET pins aka short circuit. Could it be that the MOSFET is blown too?
The charger was probably on rain or something like that so it shorted out or similar.
Here are the pictures.

The MOFET is bad and probably took out the SMPS IC with it too, so without taking chance of taking out the new MOSFET I would replace the SMPS IC at the same time. The resistors do look like 1R3.

[Morsus]

Re: Identifying burned SMD resistors

Sorry I am a bit new to all of this, SMPS IC?

1R3 would be 1kOhm right?
Could all 3 resistors be the same or as gabiz_ro said could be one with different value?

Will take out and check the MOSFET in the morning, I will let you know.

[budm]

Re: Identifying burned SMD resistors

Sorry I am a bit new to all of this, SMPS IC?

1R3 would be 1kOhm right?
Could all 3 resistors be the same or as gabiz_ro said could be one with different value?

Will take out and check the MOSFET in the morning, I will let you know.

http://www.hobby-hour.com/electronic...-resistors.php

SMPS IC: Switch Mode Power Supply IC.

[Morsus]

Re: Identifying burned SMD resistors

I am still not sure witch element is that. I googled it but cant find anything similar. Sorry :/

[petehall347]

Re: Identifying burned SMD resistors

1r3 is 1.3 ohms if i remember right

[budm]

Re: Identifying burned SMD resistors

How to read SMD resistor is on that link I gave in my post 8.
Or are you talking about the SMPS IC which is the 8-PIN SMD device on the bottom side of the board top left side?
https://www.badcaps.net/forum/attach...2&d=1495805206

[Morsus]

Re: Identifying burned SMD resistors

1r3 is 1.3 ohms if i remember right

Yes, same value in the table .

Or are you talking about the SMPS IC which is the 8-PIN SMD device on the bottom side of the board top left side?

I understand now, thanks.
Markings on SMPS IC are UC3844A DP4J0100 which is probably this:
http://pdf1.alldatasheet.com/datashe...S/UC3844A.html

Is there a way to test these to see if its broken or not? (I would love if not )

[budm]

Re: Identifying burned SMD resistors

There is no way to test it 100% with what you have, you can try checking the resistance and see what you get between output pin 6 and GND pin 5, output pin 6 and pin 7 VI, VI pin 7 and GND pin 5. You will do this with MOSFET removed first.