AP2764AI Fet Shorted In Dell LCD Monitor
This was brought to my shop for repair. It is a Dell LCD screen and it was dead.
I could not find a model number on it. The only numbers I could find was this.
These numbers were revealed the moment I took the LCD stand off. As you can see four screws has to come off. Once I did that, this was revealed.
A well shielded LCD screen. Few flex cables were inserted in and it has to be unplugged in order to get the printed circuit.
This is the power buttons cable and it was not clearly seen and I almost ripped the cable off.
Another cable to be taken off before the actual board was revealed.
Finally I got to the board. It was an ok board, not too messy. A quick look for bad soldering joint or cold one but it was all fine. I took the board off and checked for voltages on the main capacitor without power plugged in. I want to see if the capacitor has discharged or not. Look what I found.
The capacitor was still holding charge which means one thing that something is shorted along the way and was not allowing this capacitor to discharge. I discharged it right away and looked for something nearby that was shorted. Right away I spotted this.
There was a shorted fuse resistor right next to the main capacitor.
Resistors do not just get shorted out, something else was wrong there and I have to find out.
I used my LOPT/FBT tester and it was giving me that something is shorted out. Another version of this LOPT tester is called as Blue Ring tester. Since the capacitor was getting power and holding the charge, that means, it is was fine.
Now, either the diodes or the Mosfet were shorted out. I soldered the pins of the mosfet and when I checked again look what I got.
My meter reading was in the green and this means the Mosfet is shorted. I took it off board and tested it; it was shorted out for sure.
The part number is AP2764AI. It is 650 volts and rated 9 Amp. You can take a look at the datasheet by clicking on the photo below:
The moment I replaced that along with the bad resistor, the LCD came back to life.
Mission Accomplished.
This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.
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https://jestineyong.com/translation-units-charging-base-repaired/
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Parasuraman
October 10, 2017 at 9:58 am
Very professional and systematic approach! Well explained! Love to read such articles!
Robert Calk
October 10, 2017 at 10:41 am
Good job, Waleed. You are right to never assume that the primary filter capacitors are discharged.
Justice
October 10, 2017 at 1:12 pm
Mmmm another great article, 100% very interesting to read keep on with wonderful contribution.
Yousef
October 10, 2017 at 1:52 pm
Hi Waleed,
Thank you for the great article.
Can you please explain the following sentence:
"The capacitor was still holding charge which means one thing that something is shorted along the way and was not allowing this capacitor to discharge."
Muhammad Ashfaq
October 11, 2017 at 12:41 pm
yes dear if pwr supply cct was ok the capacitor 315v not carry. if this symptom is continue the some components are still damaged.this is my onion.
Waleed Rishmawi
October 12, 2017 at 11:15 am
The mosfet was shorted not allowing the screen to come on therefore the capacitor was still holding charge
Humphrey Kimathi
October 10, 2017 at 1:59 pm
******Resistors do not just get shorted out, something else was wrong there and I have to find out*** (Was the resistor shorted or open? i expect a resistor to open if there is a shorted component ahead. kindly clarify this Waleed)
Regards Humphrey Kimathi
KENYA
Waleed Rishmawi
October 12, 2017 at 11:11 am
It was open not shorted
Waleed Rishmawi
October 12, 2017 at 11:13 am
The resister fuse was open not shorted. The mosfet was shorted that did not allow the capacitor to discharge.
Humphrey Kimathi
October 12, 2017 at 9:56 pm
Got it, Thanks
Humphrey
suranga Electronics
October 10, 2017 at 5:22 pm
Mr-Waleed Rishmawi,
very Good Switching power supply Repair.
Albert van Bemmelen
October 10, 2017 at 7:27 pm
Good clean repair with nice datasheet from the replaced 600V Mosfet!
Michael Ripley
October 10, 2017 at 10:04 pm
The resistor is a 0.2 ohm fusible resistor. Surely it was okay or open circuit? I've never seen a shorted resistor.
Good repair all the same.
Waleed Rishmawi
October 12, 2017 at 11:10 am
It was open not shorted.
John
October 12, 2017 at 9:52 pm
Nicely done sir please send more
moscotechng
October 13, 2017 at 10:44 pm
Nice and informative article. Thank you and weldone
sizwe
December 28, 2017 at 10:17 pm
Could anyone help me with how to get on google a schematic /circuit diagram of a tv set as when I try I do not get the specific one I need.
Thanks
Sizwe