ELBA tower fan keeps blowing resistor

[mikey5791]

Hi all,
Got this ELBA tower fan model ETWF-B3740RC from my sister saying her technician could not repair it.
Upon opening the plastic case, I found one resistor(brown,black,black,gold)at R1 slightly charred. On the pcb, R1 has 10R 1W silk printed. I tested the original resistor using a digital multimeter and it showed nothing and conclude it must be faulty. So, I replaced with a 10ohm metal film resistor of a bigger size. Upon power on, I heard a spark and the new replaced resistor is blown.

The 2A glass fuse still has continuity and I do not see any other burned component beside the 10 ohm resistor.
Can someone experience to assist and guide me where else to check for any short or fault causing the resistor to blow. Appreciate your help and patience to reduce electrical aplliance being thrown to dumpster.

[R_J]

U1 is likely blown, Check resistance between 5or6 and 7or8
I would also replace C4 and maybe the other 2 electrolytic's as well

[mikey5791]

Hi R J,
U1 is marked D3845A OB2223AP which is a 8 pin pwm power switch. I used digital multimeter (scale 200 ohm resistance) black probe on pin 5 drain and red probe on pin 6 drain, then black probe on pin 7 ground and red probe on pin 8. Both showed reading of 0.9 ohm. Is the reading mean U1 is blown and need replacement? Kindly advise.

[R_J]

Originally Posted by mikey5791

Hi R J,
U1 is marked D3845A OB2223AP which is a 8 pin pwm power switch. I used digital multimeter (scale 200 ohm resistance) black probe on pin 5 drain and red probe on pin 6 drain, then black probe on pin 7 ground and red probe on pin 8. Both showed reading of 0.9 ohm. Is the reading mean U1 is blown and need replacement? Kindly advise.

Pins 5&6 are connected together, pins 7&8 are also connected together, so just check the resistance between the two pins 5&7
If C4 is the 10µf cap I would stick with that value, if you go higher you may have startup issues.

[stj]

sounds bad, but test again off the board.
also, replace the 10uf cap with 22uf 50v

[petehall347]

L1 looks a bit iffy

[mikey5791]

Hi stj,
Noted. Will test U1 off the board to be sure.
Will try replace the 10uf 50v cap with 22uf or higher.

Petehall347,
L1 is a 3.3MH 1W (orange, orange,red,grey)axial inductor. It has a crack on the body. I tested it using digital multimeter on 200 ohm resistance and got reading of 1.5 ohm on board.
Is this low reading considered bad?

[stj]

the 3845 can have a startup cap as high as 47uf and still start up without noticeable delay - 10uf is going to dry out faster.

[R_J]

Originally Posted by stj

the 3845 can have a startup cap as high as 47uf and still start up without noticeable delay - 10uf is going to dry out faster.

It's not a 3845 it is a OB2223AP, d3845 is a date code

[mikey5791]

Hi R J,
Checked the resistance between pins 5&7 at U1 and got reading 14.1 ohm.
Then i checked the resistance between pins 6&8 at U1 and got same reading of 14.1 ohm. Is the 8 pin pwm OB2223AP confirmed bad?
Btw i will stick with the 10uf50v cap at C4.

[R_J]

It sure looks like it is bad, the internal mosfet has 14Ω across drain and source, it should be basically open. It could also be something else that is bad so start by removing the ic and checking the resistance again.

[kaboom]

You don't need any of that.
Superfluous stuff to lights some LEDs, and give pushbutton speed/oscillate control.

Replace with a rotary switch to change speeds of the main motor, and an SPST switch to control the oscillate motor.


No need for any "confirmation;" the OB2223 has burn marks.

And do not replace an MOX resistor with a film one, especially when used as a "fuse-istor."
That OnBright IC is a non-isolated buck converter. The 2 larger electros should be replaced, and the 3 diodes checked/replaced.

[mikey5791]

Originally Posted by R_J

It sure looks like it is bad, the internal mosfet has 14Ω across drain and source, it should be basically open. It could also be something else that is bad so start by removing the ic and checking the resistance again.

Checked U1 off board for resistance and between pin 5&7 and 6&8 both reads 100.9 ohm.
I bought some new pwm of OB2223AP but it has only 7 pins, strange since the old one has 8 pins. The resistance on the new pwm on pin 6&8 is "1" but i can't test pin 5&7 since there is no pin 7. Should i replace the old pwm with the new one?

Btw, i will replace the electrolytics at C2 &C5 respectively. The resistor at R6 (100 ohm) reads 68.6 ohm off board. Can i continue to use it?

[R_J]

What do you mean by: The resistance on the new pwm on pin 6&8 is "1" ? 1 what? 1Ω? if that is correct the ic is defective because pin 8 is ground and pin 6 is the drain. What kind of meter are you using? maybe it needs a new battery.

Download the datasheet.
Pin 7 is not used on some versions (likely On-bright OB2223FAP) Note the F in the lower left of the ic

[mikey5791]

Originally Posted by R_J

What do you mean by: The resistance on the new pwm on pin 6&8 is "1" ? 1 what? 1Ω? if that is correct the ic is defective because pin 8 is ground and pin 6 is the drain. What kind of meter are you using? maybe it needs a new battery.

Download the datasheet.
Pin 7 is not used on some versions (likely On-bright OB2223FAP) Note the F in the lower left of the ic

Fyi, "1" on my digital multimeter means infinite or over the range. I selected 200 ohm resistance scale when touching probes on pin 6&8. But when i probe on the old pwm pin 6&8, it gives resistance 100.9 ohm. Is this old pwm still good?

[CapLeaker]

Originally Posted by mikey5791

Fyi, "1" on my digital multimeter means infinite or over the range. I selected 200 ohm resistance scale when touching probes on pin 6&8. But when i probe on the old pwm pin 6&8, it gives resistance 100.9 ohm. Is this old pwm still good?

One word: nope.

[R_J]

The old pwm is likely bad, that is why it why it opened R1 resistor. Try checking the resistance between pin 4 and 5

[mikey5791]

Originally Posted by R_J

The old pwm is likely bad, that is why it why it opened R1 resistor. Try checking the resistance between pin 4 and 5

The resistance between pin 4 &5 is 8.7 ohm on the old pwm measured off board. The old pwm is bad and that is why it keeps blowing the R1 10 ohm resistor. I will replace it with a new one and see if it works.

[mikey5791]

Hi all,
Just now i replaced a new pwm at U1, 10 ohm resistor at R1, 3.3MH 1W axial inductor at L1, 4.7uf400v elct. cap at C2 and 470uf25v at C5.
Total 5 components. Now the tower fan is working good.
Thank you so much for all the help and guidance.
This forum has been very helpful.