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]

Re: ELBA tower fan keeps blowing resistor

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]

Re: ELBA tower fan keeps blowing resistor

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.

[stj]

Re: ELBA tower fan keeps blowing resistor

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

[petehall347]

Re: ELBA tower fan keeps blowing resistor

L1 looks a bit iffy

[mikey5791]

Re: ELBA tower fan keeps blowing resistor

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?

[R_J]

Re: ELBA tower fan keeps blowing resistor

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]

Re: ELBA tower fan keeps blowing resistor

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]

Re: ELBA tower fan keeps blowing resistor

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]

Re: ELBA tower fan keeps blowing resistor

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]

Re: ELBA tower fan keeps blowing resistor

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]

Re: ELBA tower fan keeps blowing resistor

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]

Re: ELBA tower fan keeps blowing resistor

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]

Re: ELBA tower fan keeps blowing resistor

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]

Re: ELBA tower fan keeps blowing resistor

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?

[R_J]

Re: ELBA tower fan keeps blowing resistor

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

[CapLeaker]

Re: ELBA tower fan keeps blowing resistor

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.

[mikey5791]

Re: ELBA tower fan keeps blowing resistor

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]

Re: ELBA tower fan keeps blowing resistor

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.

[Mark_Stewart]

Re: ELBA tower fan keeps blowing resistor

Hi,
My tower fan is a Honeywell HO 5500RE but has the excat same circuit board. Symptoms for the fault was no power, no lights but no obvious defects to any components. There was power to the board, but nothing at the 5V supply which supplies the logic board at the top of the fan. Checked C5 and D3 ok. U1 outputs were not shorted so assumed ok. Eventually found R3 a 2Mohm resistor had failed open circuit. Replaced with two 1Mohm in series and 5V was restored and the fan works! Interesting circuit as the 5V output seems to have live mains to it and the 0V is supplied via a 79L05, so there is 5V difference DC, but mains on something that is marked 5V. Image shows my poorly drawn circuit diagram of the power supply side.
Also was initially puzzled by the fan wiring a Shanhu SHM-40 seven wire three speed fan. Some details here https://electronics.stackexchange.co...om-a-tower-fan
What puzzled me is that the live (brown wire) goes to the motor and returns to the board via the grey wire. Presumably there is a thermal fuse in the motor which would kill the supply to the board and would show the same no power, no lights failure.