TV LG RZ 29FB51RX no picture.

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piotrekn95

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Hi. I've got a problem with old lg's tv. Everything was ok, while watching tv suddenly go stand-by. When I push a button on tv, I heard a relay, than sound is going through the speakers but no picture is in

Now, when tv is on stand-by, LED diode is emitting red color with normal intensivity. But, when I push a button to start tv, led is lighting much lower, I am hearing a sound like a coil, (I check using a normal a4 paper - when I start tv, the sheet was glued to screen ). There is maybe 4 seconds, and tv is going back to stand-by.

I opened case, and I didn't saw the lamp is incandescencing. I checked the board about bad soldering, but it nothing helps.

I'm not freaky into tv service, but I have a little knowledge about electronics. I have a multimeter, and service instruction also.

Help me , what I have to check first, where to check the voltage.

Sorry for my language isn't fluently.

Cheers.
Peter
 

check the filament for glowing. if it is not glowing then check the horizontal ouput transistor. if its short replace it. check the b+ 110vdc at smps o/p
 
Now I checked, and filament is not glowing. I also checked H -output transistor 2SC5905 and it's not shorted. Tommorow I will check B+ voltage.
 

if b+ voltage is ok as mentioned in servicemanual/schematic then disconect the deflection yoke conector and switch on the set. if set switches on and if their is a filament glowing then yoke may be short.
 

If A4 paper is sticking to the screen, upon turn on than no need to check fly-back transistor or B+ voltage the problem may be somewhere else because high voltage circuit is working and you do have high voltage. One advise though there are very very dangerous voltages present unless you know what you are doing I advise not to go in there. Even the tv disconnected from sourse some caps may be charged. You may need oscilloscope to trouble-shoot the problem and the service manual or schematic. My guess is the ic responcible for rgb drive even the sound is working so all the low voltages are present and they are derived from the fly back transformer. You didn't mentioned if you have schematic for this set. Also I would like to add that carefully check for cold solder joints using a magnifying glass when the tv is not on. You may get lucky.

Here is a link for the schematic or service manual.
https://www.eserviceinfo.com/index....+or+RE-29FB51RQ+or+RE-32FZ30RQ+or+RZ-29FB51RX
 
Last edited:
brut007 said it is true . before atempting to service the set wait for 10 minutes , so that capacitors will be discharged. always
wear a shoe . crt anode will store 20kv voltage
 
burt007 - thanks for advice, of course I am very carefully with working, I'm attending to electrical school so I know how dangerous it could be.

- - - Updated - - -

I found IC501S - it's micronas DDP 3315C . It's not mounted on mainboard, thats why I cannot find him. I will use yours advice and resolder it. If it doesn't help, I'll start to look for another DDP.

Cheers
 

I checked B+ and it has 134.5 V. So fbt is working correctly?
 

are you hearing any type of sound from fbt. to find fbt is generating high voltage check at pin6 of vertical o/p ic301 la7845
it should be 14v.if 14v is present then fbt is working
 
I checked LA7845 and on the 6th pinount is only 12,3V not 14. Could be a defected ic?
 

in the schematic it is 14v . now check 28v across the d413 cathode side if it is present then check the filament it should be glowing. check in darkness
 
I checked in darkness, and you're right. When I power on tv the filament is glowing for a few seconds and tv is turning back to stand-by.
 

if tv goes to standby then it goes to protection mode. some thing may be short . now you disconect the yoke conector (p401)from main board. it is located near the fbt. do this after removing the mains chord from mains outlet socket.
and switch on the tv without yoke conection. now observe that tv goes to the stand by or not. and report here
 


Could also be high voltage protection circuit kicking in if high voltage exceeds to dangerous level. Meaning a short in fly back transformer in primary side which is common in old tvs.
 

I disconnected yoke connector but tv is still going to stand by.
 

tv goes to standby because their may be number of reasons.to find out the reason do the following steps.

1) remove the resistor r075 3k conected pin32 of ic001 sda5555

2) remove the resistor r331 1k conected to vprot line as shown in the schematic

and switch on the tv without yoke conection and observe it goes to std by or not
 
I removed this two resistors but tv still going back to standby. I'm still thinking about la7845 .
 

ok replace the ic la7845 , i also think it may be short. replace the resistors. as their position replace the yoke conector and we will see what happens.
 
find the voltages on microcontroller ic001 sda5555 described as below.
1) pin 9 vdd2.5v
2) pin 11 vdd3.3v
3) pin 13 vdd2.5v
4) pin 30 vdd3.3v
5) pin 33 rst
6) pin 37 vdd2.7v
7) pin42 vdd 2.5v
find these voltages it should be matching & find the voltage on rst pin33
8) pin44 vdd 3.3v
 
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