Thorn 42THL3DS1 no backlight sound ok

[maxvalutech]

This TV a generic from China is a smart model with a setup I have not encountered before. At switch on green light displays - no remote control and no response from any buttons including on/off. The green is probably the on colour. PSU seems OK with output voltages including 24v present on what I take to be backlight board PPW-LE42AT-0(A) REV0.4. Due no input working can't be sure but no picture seen - sound ok

[attainteddragon]

Re: Thorn 42THL3DS1 no backlight sound ok

voltage listings on the connector that goes to the main board in stby and after power on is applied.

pin name/number, voltage in stby, voltage after power on is applied.

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

Will read these and post a little later but basically there is no standby as set seems to be locked at astartup step and not responding to any inputs. When switched on at pp all the voltages come up but nought happens and to power off the pp has to be turned off.

[dskall]

Re: Thorn 42THL3DS1 no backlight sound ok

Sounding like an eeprom problem. Try freezing eeprom

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

Thanks dskall I was afraid someone would say that! Will take the voltages again then pull the main to see where eeprom is if marked - nothing much found on search under Thorn brand but the stand is a large oval chrome spiral affair that may bring forth other better known name - will take pic for post.

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

Checked all voltages out of PSU and all spot on and as they should be if set operating normally including 24v and 3.5v to inverter but nothing I do gets even a flicker. The only 8 pin ic on main can't read its type but tried shorting pins 5 and 6 at switch on - nothing at all and green light remains steady at all times. Pic of a stand herewith to see if someone knows other brand name/s.

[dskall]

Re: Thorn 42THL3DS1 no backlight sound ok

You're getting ps_on? You have sound so would think it turned on. You sure about no image on screen?

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

My problem here is I don't have a dtv input available and i use av input for testing but I can't change anything. The owner advised "have sound but no picture". Frustrating as we have satellite TV with HDMI input so will need to find a normal source to check as I do have suspicion set is working but control buttons are not for some reason.

[dskall]

Re: Thorn 42THL3DS1 no backlight sound ok

Need to check voltages at buttons and ir for changes in voltage when you push buttons.

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

Thanks dskall I'll do that. Now a correction I managed to find owner who advised the set was going normally when it just stopped and went into the state it is now totally unresponsive to either remote which she now can't find or the button inputs.

[dskall]

Re: Thorn 42THL3DS1 no backlight sound ok

Well now i'm back to freezing eeprom

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

Voltages as each button pressed - input 1.05 menu 1.36 PR+ 0.35 pr- 0.67 vol+ 1.79 vol- 2.09 on/off sends static 3.30 down to zero. Can the tcon be coming into play as the problem here - it does have direct input into the inverter board.
Regarding eeprom I haven't any source of freeze but did try ice cube on the suspect ic but no result.

[budm]

Re: Thorn 42THL3DS1 no backlight sound ok

The PS-ON is working otherwise you will not have 24VDC feeding that LED driver board.
I see the small flt cable on the LED driver board and it goes to the T-CON board, the BL-ON and the dimming are being routed from the main board through the T-CON.
We need good clear pictures of the T-CON and see how it is connected to the LED driver board and the main board, pictures of the LED driver board too.
What is the LCD panel number?

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

Hi Budm the panel is LC420EUN (PE) (F1) and the tcon and led circuit board (which I refer to as inverter) are also by the LC display co. Also I now find this set is 3D as well as Smart. Will try for clear pics in sunlight tomorrow as flash reflecting too much. Fuses on both boards are OK and no obvious problems.

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

Well woke up to rain with thunderstorms so had to get flash pics anyway. On the mainboard in middle of pic is a red based connector with 3 wires reading o.5v 3.5v Gnd and the fuse under that connector is OK. The inverter board has 24.6v at fuse and on pos leg of both ecaps. The small strap runs to it from tcon which only has the usual main board connection to it. To me it seems the set having gone off due to whatever tried to restart itself by turning PSU back on OK then got to backlight turn on stage where it has locked up. But as input buttons work but don't activate anything I'm now inclined to a main board problem. What I don't know is when does eeprom kick in - is it at display logo stage or earlier but I don't think it has anything to do with backlight operation. So some ic on main is not cooperating with voltage signals???

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

Pics

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

To bring this post up to date I note that this set is marketed under several brands inc Bush/Argos/Ferguson and Blauplankt or some such. It also seems to have something to do with LG as very similar to 42LA620V. The EU sets use scart inputs and our main board is different. When trolling for info came across same main for sale locally but for 55" screen so decided to buy although a bit more than I like to pay. Took a couple of weeks to arrive upon which I checked board against board and connector voltages and inputs - all the same so put board in and got standby red - pushed on button and was monitoring for backlight when a familiar smell indicated component in trouble - switched off at pp and yes a small 3 leg ic overheated and burnt (see pic top lhs near EM11). So that was that. In my comparing I noticed caps in old one in audio section were very slightly swollen so swapped these from new board but made no difference to start. The set has all the correct voltages in the right places but is in a self induced coma!! Now, am considering swapping eeprom (UF11) from new to old board and would like some of your thoughts on that i.e.
55" eeprom to 42".

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

Pic for above postu

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

Any comment on what is likely to happen using the changed over eeprom as suggested above?
Also is there somewhere I can find out in simple language the processes an eeprom goes thru at start up?

[maxvalutech]

Re: Thorn 42THL3DS1 no backlight sound ok

Well what a dunce I am. Misread the designation of the burnt component which is shown on the underside of mainboard T.MSD309.B81C 12716. Although a bit bigger than others it is transistor QM12. Can't find a schematic that relates and the component designations suggest they refer to C smd cap R resistor E electrolytic etc and the second letter to which circuit function and the number then being sequence but starting at 11. Eeprom is UF11 the F being for flash. The main processor is just U1. Now I really don't know but M could be for main power. Problem part of the board only has 5v and 12v. Separate audio input has 24v on left bottom of board. Only difference I can see in comparison of the boards is screen manufacturer so not likely an Eeprom swap would work but almost no hope of getting a Thorn program as these sets marketed by appliance rental mob only interested in $$$s. Bush etc do have repair kits on eBay but can't see 42" one.