Toshiba LED TV Dead No Power
I received a Toshiba TV for repair that had a ‘dead’ condition (no power). Upon speaking with the customer, I learned that the TV had not been used for the past few years. Due to financial constraints, the customer hadn’t mentioned that they had previously had it checked by another technician; instead, they simply asked me to assess the possibility of fixing it. To verify the issue, I connected the TV to my series test board and turned it on; I found it to be completely dead, with no standby light illuminated. I couldn’t inspect it at that time because I had some other work. So next day I took the Tv for the repair.
When Opened the unit, I found it was having Cobwebs on everywhere in circuits.
I was conflicted about whether to proceed or not because I have a severe dust allergy; in fact, it was precisely because of this dust issue that I had stopped working on desktop computers— those who work on computers would understand—since all my earnings would end up being spent on medication.
I packed everything & kept it a side, Then I wondered how long I would hold onto it; I knew that customer well, and he, too, was going through a difficult time. So, I decided to help him. So next day in early I decide to clean up the Tv from inside.
Cleaned the TV thoroughly. Now connected the Tv on my series lamp board & powered & measured the Voltages on Mains Filter Capacitor it gives reading of 330v seems OK, but there is no any Output voltage on secondary side. So removed SMP Board from further testing.
Found Burn mark below the SMPS PCB & chassis, PCB burn mark is near the Electrical Isolation track, showing heavy arching in this area. But Voltage on mains filter is ok indicating up to capacitor everything is OK. Now checked secondary output voltages I found all voltages are missing i.e. 5v /12v & led driver voltages. aux supply showing 6v seems very low it should be over 15v.
so removed Mosfet for cold test Mosfet found OK, checked primary side components on PCB on cold testing seems Ok. Now back of the PCB I found one PWM IC
As per the IC Datasheet I found pin no.1 is VCC pin, so again checked for Startup voltage on this line it shows 6v, checked startup resistors all found Ok on cold test. So may be PWM Ic is the culprit for the symptom.
I do not have this pwm IC marked with TEA1733, so I arranged CA888 module from my nearby part vendor,
Removed MOSFET & PWM IC first & checked surrounding components on cold testing nothing else is suspicious. Hence installed the module.
The issue now is that this power supply uses two optocoupler’s; one wire (the white wire from the CA888 module) connects to pin 4 of an Optocoupler, but which Optocoupler should provide the feedback to the PWM? Upon tracing the circuit, I discovered that one Optocoupler is for the standby 5V supply, while the other is for feedback. After confirming this, I desoldered pin 4 of the feedback Optocoupler and soldered the white wire to it.
After wiring I turned on the Power supply but still there is no output.so removed the power supply from the power, discharged the mains capacitor & again start to search faulty components on secondary side on cold test & found 12v supply output diodes one is shorted & one is leak.
Upon checking the other components on this side, I found them all to be within the correct range. Therefore, I replaced the two faulty diodes (SR310) with SR5100 diodes and powered the unit back ON.
& checked secondary Output voltages. Now all voltages are in normal range
Checked LED Driver voltage it also shows 56v.
Now assembled everything back to see the result, but it dashed all my hopes.
Found Screen Panel is already Damaged dark patch on one side corner with vertical & horizontal lines, I knew that no further work could be done due to certain limitations on the customer’s part, so I called the customer in and explained the fault and the repair costs. When I turned on the TV in front of the customer, they remarked that the screen had looked the same even when the TV was functioning in same conditions; however, the unit had made a noise, after which it shut down completely and had remained in that state ever since.
The customer was informed that spending money on it would be a waste; he told me to keep any parts that might be useful and to scrap the rest.
This article was prepared for you by Yogesh Panchal who works as a Computer Hardware Engineer in Mumbai India.
P.S- Do you know of any your friends who would benefit from this content that you are reading now? If so, forward this website to your friends or you can invite your friends to subscribe to my newsletter for free in this Link.
Note: You can check his previous repair articles on Limit Switch Working
(1)Dislikes
(0)
