electronics, repairs, service manuals and datasheets discussion community for the repairs professionals and technicians
FAQSearchMembersGroupsRegisterProfilePM'sLogin/Out
Need help diagnosing a problem (LCD TV - no picture)

 
Post new topic   Reply to topic    Electronic equipment repair and service manual search discussion Forum Index -> Equipment Repairs
View previous topic :: View next topic  
Author Message
drabina



Joined: 04 Aug 2010
Posts: 3

PostPosted: Thu Aug 05, 2010 12:43 pm    Post subject: Need help diagnosing a problem (LCD TV - no picture) Reply with quote

I have Samsung LN-T3242H LCD TV. When I turn it on, I get the sound (welcome melody), the red light near the power button flashes, I see backlight on for about 1 second and then everything goes dark. Here is what I found/tested so far:

1. I can hear audio even with the dark screen
2. There is a faint image (flashlight test)
3. Power board supplies 24.4V on all pins to the inverter
4. There are no visible bulging or leaking on any of the capacitors
5. During the 1 second when the backlight is on I do not see any obvious dark lines that would indicate a burnt bulb

Most likely it is inverter. I can get new one and replace it but I would like to be sure that it is it and not the lamps. What else should I check to further diagnose the problem?

Thanks.
Back to top
View user's profile Send private message
jts1957



Joined: 24 Nov 2008
Posts: 2472
Location: Far, Far Away

PostPosted: Thu Aug 05, 2010 5:27 pm    Post subject: Reply with quote

If possible, unplug all bulbs. Plug back in one at a time, each in its own turn, unplugging each after its turn. Power up set. For each bulb tried you should see a brief white flash across the screen.
If any don't flash, you have a bad bulb. If you can arrange to physically "see" the actual bulbs during this test, so much the better.

There are at least three pins to the inverter that should NOT measure 24 volts. One is "backlite enable," that should be there and stay there whenever the set is turned on. "Backlite intensity" is the second. There had better also be at least one ground pin.
_________________
You're over there, I'm over here.
Back to top
View user's profile Send private message
drabina



Joined: 04 Aug 2010
Posts: 3

PostPosted: Thu Aug 05, 2010 5:41 pm    Post subject: Reply with quote

Thanks for replying. Unfortunately, I can't test each bulb as they are not connected by a cable but by fixed panel. So without modifying the circuit it is all or none.

What voltage does the lamp take? I could maybe connect them to something else just to see if they work.
Back to top
View user's profile Send private message
jts1957



Joined: 24 Nov 2008
Posts: 2472
Location: Far, Far Away

PostPosted: Thu Aug 05, 2010 5:53 pm    Post subject: Reply with quote

A little lite reading: http://en.wikipedia.org/wiki/Cold_cathode
_________________
You're over there, I'm over here.
Back to top
View user's profile Send private message
Dan the Tv man
Guest





PostPosted: Sun Aug 08, 2010 6:24 pm    Post subject: Lcd no picture Reply with quote

Check the inverter board,on the side of the main board for bulged top capacitors also check the fuses on the inverter board.F1,F2.If youve got a faint picture with a flashlight.Either the inverters not putting a picture on the screen or the backlights not lighting.
Back to top
minnie



Joined: 18 Aug 2005
Posts: 2877
Location: Hell

PostPosted: Sun Aug 08, 2010 9:29 pm    Post subject: Reply with quote

Usually when it lights for a second or two and goes out one of the transformers on the inverter is open. Check the transformers for holes.
Back to top
View user's profile Send private message Send e-mail
Justmanuals



Joined: 21 Aug 2004
Posts: 1949

PostPosted: Mon Aug 09, 2010 12:06 am    Post subject: Reply with quote

This Parts & Service manual can now be purchased for $11.77 and downloaded immediately after payment from http://www.justmanuals.com


[email protected]
_________________
Want To Fix Something?
http://www.manuals4you.com

Need a manual now? Instant Download
http://www.justmanuals.com
Back to top
View user's profile Send private message Send e-mail
xxdkxxx
Guest





PostPosted: Thu Mar 06, 2014 6:37 pm    Post subject: Reply with quote

I have same tv but after replacing capacitors still no picture on screen. Standby red light comes on and stays on after turning on. no sound. can you lead me to what to look for next. How can i text or check that my solder joints are done correctly on capacitors?
Back to top
SDS
Guest





PostPosted: Fri Mar 07, 2014 10:13 am    Post subject: Reply with quote

Most of the time it is the inverter board that fails if you have checked all the SMD fuses on it as Dan the Tv man suggested next check transformers.

There are 8 transformers each has 2 secondary windings, compare resistance of all 16 windings, it only takes one open secondary for inverter to not work. Transformers can be replaced individually it turns out cheaper than replacing whole inverter.

xxdkxxx: If you initially had bad electrolitics on the standby PSU due to messy power to the main board sometimes a 24C256 E²PROM gets corrupt and needs blanking before TV will power up normally.
Back to top
train123



Joined: 26 Jan 2010
Posts: 88
Location: Canada

PostPosted: Wed Mar 12, 2014 5:11 pm    Post subject: Reply with quote

What I've found is that there are too many variables to properly narrow down this type of problem. As well, the shotgun approach winds up costing too much in wasted parts purchased.
I've resorted to disassembling the panel to be able to physically view the backlight. This has proven to work well on both LCD and LED units. Since the flash happens quickly, video the unit and play it back slower.
**Word of caution**
The LCD display itself is easily damaged and so are the connecting ribbons to the panel driver boards.
Take careful note of the order of the light defuser panels because I've seen up to 5 different layers and they need to be replaced in the same order.
Also ensure everything is clean because any dirt or dust behind the LCD display will show up as black spots when viewing the picture.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    Electronic equipment repair and service manual search discussion Forum Index -> Equipment Repairs All times are GMT
Page 1 of 1

 
Jump to:  
You can post new topics in this forum
You can reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Електроника София - Service Manuals Free Download - Prikachi - Service Diagrams

Free TV Schematics Download - HARDW.net - Pinout Master - Jabse Search - Jabse.InK  - Pulsator

Connector Pinout Forum - Новини - SnimkiOt.com - безплатен DNS - Whois разузнаване - Poblizo.com : пътешествия