Hitachi LE50EC04aud no led backlight

[maxvalutech]

Came by this set about a year ago when owner gave it to me "not working" however he must have forgot about side buttons as the remote control was the problem. My grandson has used it since but now "no picture comes up". Immediately suspected blown LEDs and on testing got 365v on main cap and led lead went up over 140v then slowly diminished. Pulled the led lead from connector and retested but same result! No sign of any flash from the LEDs at all. There is standby OK and turning on the set appears to start with a change to blue light which stays on. When I took the back off I swore a couple of times on seeing MSD main board and Leke PSU. Pulled the PSU out to go over it and noted one small area seemed to have dried gel like substance there and a very small bubble or two of it as well. Now I have no idea what this is for or from but perhaps gunk when manufactured. It covers ic2 and a few items near it. Any ideas anyone?

[CapLeaker]

Re: Hitachi LE50EC04aud no led backlight

First thing I would do is taking that PSU out and see if you can find a pinout on these connectors top right that go to the main board.

Fact is: The PSU always produces STBY voltage. Make sure it is there. This STBY voltage is continuously fed to the main board. Once you press the power button on the TV, the main IC on the main board returns PSon and BLon to the PSU. The PSU turns on all voltage rails with PSon and it will turn on the back lights with BLon. PSon and BLon should be at least 2.5V.

Find the STBY power, try to turn on the TV and probe the other pins. A missing PSon or BLon will tell you the main board is bad.

To test the PSU (you need the pinout), unplug the main board from PSU, take two 1k resistors and jump STBY to PSon and STBY to Blon. Plug the TV into mains power and all voltage rails should be running and the back lights should be running.

[Andrew F. Ali]

Re: Hitachi LE50EC04aud no led backlight

From what I have read, I interpret the PSU and Main Bd. to be OK. Your problem is the LED backlights. one or a few of the LEDs are open so you get the backlight supply voltage shooting to 365V and when the Driver does not 'see' any load it shuts down in protect mode. More than likely if you hook up a source to the inputs you may get audio and flashing a light on the screen you may see a dim picture.

[maxvalutech]

Re: Hitachi LE50EC04aud no led backlight

Yes I'm sure the main board is doing its job and though I haven't been able to see menu etc on screen I'm sure it wasn't dark enough for that test. Initial diagnosis by me was I'm certain its a blown led but I was put off by when led lead was disconnected the voltage to led connector still ran down. Andrew F has now pointed to no load being the cause of that which leads to protection circuit turning off. Other threads I read didn't cover that aspect. Is there any "load" I can connect in place of LEDs ? Large resistor, bulbs, or whatever to be certain of the diagnosis before I start the big job. I have been "caught" recently when I found all LEDs working well on a set when I was sure there was a problem with them but it was PSU that had a fault after all. The difference there was that the LEDs did flash briefly but not in this case.

[R_J]

Re: Hitachi LE50EC04aud no led backlight

If the voltage on the leads going to the backlights comes up to 140 volts, the led's should light for a second or two, if they are good, BUT if even one is open (they are in series) you will not get a flash at all, and it will shut down. You could get one of those led testers to test the operation of the leds before opening the panel.

[maxvalutech]

Re: Hitachi LE50EC04aud no led backlight

Well I'm flummoxed!! I decided to put the set back together to take back with me to where I mainly live and tinker (1200km from where I am now). I did give the back of the PSU where that gunk was a good scrub with a stiff brush then replaced it in set and put the back on etc. Decided to see if standby still there and it was so hit the on button to see if blue light came an stayed on - it did and so did the screen !! Got menu etc up and all now going normally. Was the gunk the problem ? If so where did it come from as the set area the PSU backs onto is clean and clear of anything. Was it a connection - who knows. By the way no voltage info back or front on PSU and none on front of main board which I did not touch. As for my diagnosing skills their RS. Oh edited because I just saw R_J post - damn good idea.

[R_J]

Re: Hitachi LE50EC04aud no led backlight

I don't know what that GUNK was (taste it ) It is possible it was causing the problem, you could also have a poor solder connection. if it keeps working, give the board a few tapps with something (plastic screwdriver handle) or poke the board with an insulated stick (wood/plastic chopstick) and see if it stays on.

The other thing could be a bad connection inside the panel on either one of the led's or more likely one of the plugs on the led strips. I have seen this before. tapping the back of the panel might cause the fault to show up.

[maxvalutech]

Re: Hitachi LE50EC04aud no led backlight

Good advice. I must add there are 2 wires going to 3 pin connector top right of PSU and marked on/off and adj. I recall now the wired plug was very hard to disconnect - almost like it was glued together I really had to apply force with flat screwdriver both sides to get the plug moving. So I did push that connector together firmly when reassembling and thinking about it now that connector being marked adj it is probably related to backlighting. Will give the PSU a run over with the heat gun and put set on test.

[R_J]

Re: Hitachi LE50EC04aud no led backlight

that would be for the backlight adjust and backlight on/off, check the solder connections on that plug just in case. also wiggle that cable, sometimes the leads get loose, they are cheap connectors.

[maxvalutech]

Re: Hitachi LE50EC04aud no led backlight

Just to update. Turning on proved to be intermittent. I reseated and soldered led on/off connector on PSU and then was back to square one except that now 141v was stable on driver leads. Took voltages with set in standby and that seemed normal but checking them at blue light on I found no voltage to speakers from main and only 0.1v showing on 2wire connection to led on/off adj. Oh oh eeprom springs to mind in context with MSD main including finding any info or firmware. But now the strange part as when I took the 2wire out of the main it then brought up the pins to around 5v and when I immediately plugged that connector back in the backlights turned on, the Hitachi logo came up and set was on normally. But it won't turn on from scratch. I have done the sequence above a few times with same result - taking that connector apart seems to kickstart the main into action. All suggestions and comments are welcomed.

[maxvalutech]

Re: Hitachi LE50EC04aud no led backlight

Got into service manual with Source2580 and would like to know what the various headings actually refer to . e.g. general settings brings up sub menus for stuff I know abit about but some others are a mystery. Did do TV init in hope of resetting basics and the set did start again for a retune etc.

[maxvalutech]

Re: Hitachi LE50EC04aud no led backlight

Turn on again intermittent about once every seven attempts however managed to get av source connected to my satellite box and when it did start normally I ran it for several hours no problem but after switch off intermittent again but is evident that set actually mostly starts with audio coming on just no backlights. This circuit must be different with 141v now steady on driver leads but no LEDs on until on/off signal received from mainboard. That signal not always generating but when it does it must close the otherwise open LED circuit. Time to hunt for a dry joint on mainboard I think.

[maxvalutech]

Re: Hitachi LE50EC04aud no led backlight

Ran the heat gun over suspect area and components with result the set starts now as it should except I have lost audio !! Isn't this a great hobby !!

[CapLeaker]

Re: Hitachi LE50EC04aud no led backlight

I hope it isn't anything stupid, like something stuck or bent inside the head phones connector, audio muted or set to a different output, etc.

[maxvalutech]

Re: Hitachi LE50EC04aud no led backlight

No the audio was also somewhat intermittent and it seems my working over of the board has tipped the audio over the edge so to speak.

[maxvalutech]

Re: Hitachi LE50EC04aud no led backlight

Update and final post for this one, yes it was my finger trouble as audio plug wasn't in the connector right so that was easy in the end but would have been easier to do it right first time and check it. This is now the second set I have confidently blamed fault on LEDs string and been wrong - not knowing how the circuits are actually set up is a problem in itself and the symptoms can be misleading from set to set.