Hi Friends ,
Today i am going to share how i solved LG 32" LED TV Which is Working on Higher Voltage only (235Volts AC and more).
BACK STORY
One of my friend had an above problem since from 10 months. He tried this TV With many technicians but the problem stood unsolved. Any how he did not tried for further repair because it is working perfect at 235V AC and greater .Since he stay in industrial area their voltage level is always towards high.
Because of frequent power cut he installed UPS & he started to run this TV on UPS.Now the real problem started & TV stopped working.Question raised in his mind,Why UPS not supporting??
He checked the voltage out put UPS showing 207Volt AC,Checked the raw Voltage it is showing 235v ac and greater.He tried to Boost the voltage using stabilizer again he faced the problem TV Shut down when BUCK/BOOST Relay chatters under UPS Line. Finally he called over phone & Discussed the Issue.
HOW I REPAIRED
Now the TV is on my Work bench.In my mind many Questions .Before opening i am asking my self
since it is having SMPS What could be the reason? It has to work from 170v to 270v ac but I suspected SMPS Line sense circuit is having problem because it is switching off at lesser than 235V AC.
Before switching ON I visually checked all the component for burnt or physically damaged.Now the time is to switch on via 100W Series bulb.Checked the voltage at Big Filter Capacitor to my surprise the voltage is around 290v DC when raw ac is 220V.But here the capacitor voltage rating is 100mfd/450v .There is a circuit between rectifier to Main filter capacitor Which is known as an Active PFC circuit which is used to boost the rectified voltages to 380v to 400v DC.
.pls go through the pcb below
The main culprit is PFC IC which is not signalling pwm pluse out .Checked the ic availability in my junk pcb but not available. Tried in market luckily I got replaced but I am un happy because ic is again not functioning. Now i wanted to know the reason why the both ic not responding .I need a data sheets for FAN 7530 .Goggled in internet & downloaded the data sheet.Checked the VCC pin voltage 14v dc found within the spec ,also checked the Feed back voltage found as per spec normal.Now compared the removed & new ic with my fluke meter in ohm range .Removed ic is measuring 8ohm between compensation pin to ground .But new IC is around 12k ohms from this observations it is conformed that old ic is defenatily having problem.Now my attention is towards other components attached to this FAN7530 .The another culprit is current sense 2ohm resistors @ pin 4 found open replaced the same .Now the time to retest the unit.After powering up with 165v ac pwm pulse started coming at out put pin .
Below is an Ideal Circuit found 2nd Culprit Current sensing resistor found open.
Now the voltage at the main filter capacitor raised from 290v DC to 400v DC .I am very Happy by seeing this voltage even with the input 165Vac.This is what I required tv worked perfectly after stimulate from 165ac to 255ac using my veriac. Customer felt very happy after deliver. This is how I repaired & one of my success story.
I will be back again with my one more success repair story.
With best regards
