42lg3000 fault

[charlierfc]

Hi, ill try again with this post. The last one i kinda strung everything together!
Ok, i have a 42lg3000, i have an intermittent fault where some times the tv works fine, other times the backlight wont come on.

After a few tests when its working fine i get
24.4v to backlight on master and slave inverter
12.4 to the main board
5v to main board

When the tv is playing up the 'ON?' to the main board wont jump frpm the low volts to the 12.4 it should, there for i dont get any inverter power 0v.

I do have a slight buzz when the backlight comes on, on full power before it sets its self to the lower power. I dont know if this is relevant as when the tv is on it will work 100% untill its turned off.
Its a hit or a miss if the tv will come on, both occasions the red led will flash untill a steady blue light is on. Thanks for reading, i appreciate any input.

PS. I checked the transformers on the inverters and im getting a good reading from the connections tom66 showed somebody to check on a previous post.
Many thanks, Charlie

[tom66]

Re: 42lg3000 fault

In the fault state do you have any other voltages?

I would try, when set works, MENU held down on remote, MENU on TV for 5 seconds, if prompted for a password enter 0000. Then look for debug log, power log or error log or similar, there should be a listing of reasons for powering off.

If you see POWER_OFF_BY_ABN then suspect main board. There's a whole list of different possible errors:

    POWER_OFF_BY_CPUCMD = 0,
    POWER_OFF_BY_ABN = 1,
    POWER_OFF_BY_KEYTIMEOUT = 2,
    POWER_OFF_BY_ACDET = 3,
    POWER_OFF_BY_RESET = 4,
    POWER_OFF_BY_5VMNT = 5,
    POWER_OFF_BY_NO_POLLING = 6,
    POWER_OFF_BY_REMOTE_KEY = 16,
    POWER_OFF_BY_OFF_TIMER = 17,
    POWER_OFF_BY_SLEEP_TIMER = 18,
    POWER_OFF_BY_ABNORMAL1 = 19,
    POWER_OFF_BY_FAN_CONTROL = 20,
    POWER_OFF_BY_INSTOP_KEY = 21,
    POWER_OFF_BY_AUTO_OFF = 22,
    POWER_OFF_BY_ON_TIMER = 23,
    POWER_OFF_BY_RS232C = 24,
    POWER_OFF_BY_RESREC = 25,
    POWER_OFF_BY_RECEND = 26,
    POWER_OFF_BY_SWDOWN = 27,
    POWER_OFF_BY_LOCAL_KEY = 28,
    POWER_OFF_BY_CPU_ABNORMAL = 29,
    POWER_OFF_BY_INV_ERROR = 30,
    POWER_OFF_BY_OTA = 31,
    POWER_OFF_BY_UNKNOWN = 255

[charlierfc]

Re: 42lg3000 fault

Thanks tom ill have a look at that,the past 15 or so power off and on its worked ok, i did notice a screw a bit loose on the psu,was wondering if had something to do with a bad earth?

OK i checked the power off in the service menu, you dont get many options, though i did find a 'power off' option. I checked that but it has a limited memory. So all i have in the list is

rc
key
key
key
key
key
key
key
key
key.
i guess the rc is the remote,and key is the power button!
Ill need to check it next time it fails to turn on, though would it list it? As when it does turn on, it will remain on till its turned off. Only when its attempting to turn on i get the problems? next time it doesn turn on, ill try menu again, thanks again.

[charlierfc]

Re: 42lg3000 fault

well it done it again today, i tried the power off list for info but doesnt say anything, just the same rc rc rc
Do you think it is the main board not sending the signal to the psb to turn on the 12V?

[tom66]

Re: 42lg3000 fault

That would be my guess, what you can try doing is heating up parts of board and see if it switches on when something is heated (or the reverse, switches off when heated.)

[charlierfc]

Re: 42lg3000 fault

ill give it a go, would it be capacitors that would cause that? i was thinking more a bad chip on the main board? its very frustrating as it will work great for days then out of the blue, it wont turn on, ill press it 'on' around 5 times or so, then eventually will come on with no fault for a while.Im prepared to buy a new board for the tv, but im unsure if its the main board or the psu.

[charlierfc]

Re: 42lg3000 fault

ok, have an update with this one, after turning on the tv after a bit the tv flashes on and off, i mean the full screen including sound! the tv flashes on and off although the blue on light remains on.im wondering,would this be a main board fault or the psu?
iv not taken measurements when tv is flashing yet

[charlierfc]

Re: 42lg3000 fault

another bit of info, i turned the backlight down from the settings menu when it was turning the picture and sound on and off(not for anybody with epilepsy!) and it cured the pic and sound loss......so...where now? replace psu? would a bad mainboard cause this?
any help is welcomed, i will get the back off the tv and heat the psu with the backlight on full, see what happens.

[charlierfc]

Re: 42lg3000 fault

fixed!

adding this info if anybody ever has same problem.
i replaced the power unit and all is well, no buzzing or faults on startup screen remains fine with backlight up full.....