Hitachi LE55A6R9A - No backlight

[PorkfriedPanda]

Hello guys, my name is Christopher and, after watching an excellent YouTube video by MrReeceyBurger123, I decided to come and post here for help with my problem!

The video in question: https://www.youtube.com/watch?v=0uBhca7zyXI&t=604s

I'm not nearly as knowledgeable with hardware as many of you here, but I will do my best to avoid asking outright stupid questions and I won't demand spoon feeding.

However, I am at a point in this repair where I think it's best if I ask those with more experience than myself.

So this 55" Hitachi 1080p TV, LE55A6R9A came into my possession. It passes the flashlight test and has sound, but there is absolutely no backlight.

I open it up far enough to get to the power supply board. ( MP145D-1MF22-1 )

Around the 8 minute mark in the YouTube video, MrReeceyBurger123 verifies that the power supply is working correctly. Now, I can't absolutely rule out that I'm somehow doing something stupid with the multi-meter, but I get absolutely no reading on any of the lines from CN202 or CN203, which it seems plainly obvious are supposed to carry power to the LEDs.



I plug in the TV, hit power so that the light goes blue, ground the black probe on the metal part of the TV case and jam the red probe down into the "socket" until it must be touching the metal sheath in the plastic plug. I also attempted to touch it to the solder points on the underside of the PCB and that gives me nothing either. I'm getting NOTHING on CN202/CN203!



Can I go ahead and order a new power board from eBay, or is this inconclusive?

I admit I am out of my depth at the moment, but I am absolutely willing to listen and learn and do my own research.

Any advice is massively appreciated, and I am deeply respectful of the knowledge and experience everyone seems to have on here

[dkneyle]

Re: Hitachi LE55A6R9A - No backlight

If you are SURE there in no voltage at those output pins then it would be a power supply fault. If you look at the printed tracks you should be able to see how the circuit is connected and confirm exactly just what the configuration of those output pins are. Sometimes it a series type configuration, sometimes a parallel configuration. It is a very basic circuit at the LED output driver by looks of things. Check those rectifier diodes.
If you find you have volts then you probably have a failed LED in the string in the panel. USUALLY that means a write-off unless you have the skills to open up the panel and replace an LED.

[PorkfriedPanda]

Re: Hitachi LE55A6R9A - No backlight

I took this TV to learn as much as to actually fix it. If it's a write off or not really "worth it" that's not such a big issue.

I am... somewhat sure but I will double check.

My multi-meter is kind of cheap. In the video he set it to 600 volts ( Is that the right unit? Straight volts, not a x10 1/10 or whatever) My meter says 200, then 1000. I was using 200. Direct current of course. Could that cause a false non-reading?

I was getting readings other places on the power supply board, but not ( as far as I could tell ) at those points.

Bored right this minute anyhow, I'll take your advice and follow the tracks back and see if I can find voltage.

EDIT: This is the underside.

[PorkfriedPanda]

Re: Hitachi LE55A6R9A - No backlight

Okay update.

The meter is set up like this, just because I want to make sure I'm not being silly.



When I ground it, then press deep in the sockets on the actual lines that lead to the LED I get a really small reading for a split second, then nothing. At the "top" of both nearby diodes, at this setting, I get wildly, randomly fluctuating readings. Nothing at all like the video. On the "bottom" leg I get nothing as well.

On the actual points in the 'sockets' I definitely make contact, I can feel it scrape the metal and I get an *extremely* brief response from the meter, but then it drops to zero immediately.

Am I doing this wrong? Do I need a better meter? The 200milliamp for the red wire doesn't seem to read as "well," for lack of a less stupid sounding way of putting it.

*sigh*

I need to brush up on the basics for sure. Sorry for the silly questions, I just want to make sure I'm doing it correctly.

[R_J]

Re: Hitachi LE55A6R9A - No backlight

Your red probe is in the wrong plug on the meter, it should be in VΩmA NOT 10A DC, That is for measuring current and would put a short on what ever voltage you are trying to measure.
The dial is in the correct place for measuring up to 1000 volts, if the voltage is below 200 volts you can use the 200 volt range

maybe read this http://www.petervis.com/meters/dt830...tructions.html

[PorkfriedPanda]

Re: Hitachi LE55A6R9A - No backlight

Your red probe is in the wrong plug on the meter, it should be in VΩmA NOT 10A DC, That is for measuring current and would put a short on what ever voltage you are trying to measure.
The dial is in the correct place for measuring up to 1000 volts, if the voltage is below 200 volts you can use the 200 volt range

Okay thank you, I suspected I was doing all kinds of things wrong. Thanks for your patience. I hope I haven't damaged the TV, though it still seems to be basically behaving the same, so fingers crossed. I honestly don't feel torn up about losing a TV I got for free ( and I have plenty of them already at the moment, don't really need this one. ) I just don't want to damage it and miss the opportunity to get it working.

When I was at 200 with the red probe in the correct slot, I wasn't getting what the video was showing. I was getting fluctuating voltages on the "top" pin of the nearby diodes, but nothing like the video anywhere.

And believe me, I do feel silly. It even says amperage, not voltage.

EDIT: Thanks, reading the petervis link now

[R_J]

Re: Hitachi LE55A6R9A - No backlight

You should be able to measure voltage accross these two points, I would leave the leads to the led's connected if you can, the two sets of wires going to the led's in the panel are connected in series.
I can't tell from the pictures but the led voltage may be isolated from the chassis ground so when you have the ground, (black) probe on the chassis you may not measure the led voltage, but by putting the meter accros the leads going to the panel led's you should get a reading.
maybe give a larger view of this area

[PorkfriedPanda]

Re: Hitachi LE55A6R9A - No backlight

This is precisely what I was about to report. As far as I can tell, I'm not getting any voltage in that area.

With it grounded on the case, these were the results. The red marks were reading over 1000 volts, the black marks were reading nothing at all. This is with the TV plugged in and the power button pressed to take it from red light to blue light. Despite the illustration, I was doing this with the wires all plugged in! Just to be clear.



I'm testing the LED leads by jamming the red probe deep into it and feeling it scrape against the metal in there. That should work, right?

And sorry for newbing the place up! I promise I catch on quick

EDIT: When you say across these points, do you mean use the black probe and the red probe on both ends instead of simply grounding the black probe? I can try that.

[budm]

Re: Hitachi LE55A6R9A - No backlight

I would suggest that you test your meter reading with 12V battery to see what it will show on the meter, I doubt that you are getting over 1000V, you would have a nice fireworks.

[PorkfriedPanda]

Re: Hitachi LE55A6R9A - No backlight

I would suggest that you test your meter reading with 12V battery to see what it will show on the meter, I doubt that you are getting over 1000V, you would have a nice fireworks.

Makes sense, that does seem really really high.

Could the meter just be broken?

[R_J]

Re: Hitachi LE55A6R9A - No backlight

If he measured high voltage on the anode of the diodes, that could be correct as the spikes could be quite high and at a high frequency the meter may give a false reading.
Thats why I say to measure the dc voltage accross the two points I indicated

[PorkfriedPanda]

Re: Hitachi LE55A6R9A - No backlight

If he measured high voltage on the anode of the diodes, that could be correct as the spikes could be quite high and at a high frequency the meter may give a false reading.
Thats why I say to measure the dc voltage accross the two points I indicated

TV is on with the light blue. Pressing metal to metal in the socket, set to DC voltage 200, with the probes set correctly and measuring with the probes precisely where you show...

I get nothing on the meter. Bad power board after all?

[R_J]

Re: Hitachi LE55A6R9A - No backlight

You would need to connect the probes where I indicated and then turn on the tv, Its a good chance that if there is no load (ie: open led circuit) the power supply for the led's will shut down. so the voltage may only be there for a couple seconds

[PorkfriedPanda]

Re: Hitachi LE55A6R9A - No backlight

You would need to connect the probes where I indicated and then turn on the tv, Its a good chance that if there is no load (ie: open led circuit) the power supply for the led's will shut down. so the voltage may only be there for a couple seconds

Gotcha, I'll try that now!

EDIT: Okay, tried it. Powered it off and on and even turned it off and on at the wall once with the probes in place while staring at the meter. Nothing across there.

EDIT2: I'll get you that larger view, by the way. Sorry I think I missed an edit, and I read that about it being isolated from the chassis ground as well!

EDIT3: Actually, copied over from budm's ShopJimmy link!

[budm]

Re: Hitachi LE55A6R9A - No backlight

You need to find out if your meter is good and working or not first, wrong data will not help troubleshooting the problem.
If the meter is good then we need to find out if the LED driver circuit is getting the BL-ON signal to turn on that power section on or not and go from there.

Hitachi 850118727 Power Supply
http://www.shopjimmy.com/hitachi-850...wer-supply.htm

BTW, your meter does not have that high of the frequency bandwidth to measure high frequency AC Voltage.

Pictures provided by shopjimmy.

[PorkfriedPanda]

Re: Hitachi LE55A6R9A - No backlight

You need to find out if your meter is good and working or not first, wrong data will not help troubleshooting the problem.
If the meter is good then we need to find out if the LED driver circuit is getting the BL-ON signal to turn on that power section on or not and go from there.

You said 12v right?

Is a car battery a safe test?

[R_J]

Re: Hitachi LE55A6R9A - No backlight

It could be a bad power supply but it could also be an open led in the panel. I have seen more problems with bad panel led's but you would need to check them, they make a small led tester for that purpose.
Thats about all I can do from this far away.

[PorkfriedPanda]

Re: Hitachi LE55A6R9A - No backlight

It could be a bad power supply but it could also be an open led in the panel. I have seen more problems with bad panel led's but you would need to check them, they make a small led tester for that purpose.
Thats about all I can do from this far away.

Fair enough. What's the cost for the LED tester, if it's not outrageous I wouldn't mind picking it up. Probably won't be the last time I try to fix a TV, honestly.

This seem right? https://www.amazon.com/0-310V-Output.../dp/B01A1479ZS

EDIT: Can anyone recommend a not-outrageously-expensive but adequate multi-meter for this kind of work?

[R_J]

Re: Hitachi LE55A6R9A - No backlight

That is one, check around there may be others cheaper, there were posts on here about them somewhere. I think they are around $30.00
heres one http://www.ebay.com/itm/0-300V-LED-L...t_11251wt_1036

This is the model SID-GJ2C

[budm]

Re: Hitachi LE55A6R9A - No backlight

Fair enough. What's the cost for the LED tester, if it's not outrageous I wouldn't mind picking it up. Probably won't be the last time I try to fix a TV, honestly.

This seem right? https://www.amazon.com/0-310V-Output.../dp/B01A1479ZS

EDIT: Can anyone recommend a not-outrageously-expensive but adequate multi-meter for this kind of work?

That is a good tester to have.
Car 12V will be fine to see if your meter is still working or not.