Hitachi LE49S508

[krygods]

I came across this Hitachi TV that doesn't do anything when plugged in.

No standby light, power button does nothing.

The power supply is on though because all voltages are present except BL/ON.

Here are the Voltages

CON801
PS-O/F - 3.2VDC
PB adj - .14VDC
PB O/F - 0VDC
GND
GND
GND
GND
+12v - 12.37VDC
+12v - 12.37VDC
+12v - 12.37VDC
+12v - 12.37VDC

CON901
GND
KEY 0 - 3.3VDC
KEY 1 - 3.3VDC
LED G - 3.28VDC
LED R - 0.07VDC
IR IN - 5.16VDC
GND
+5V - 5.2VDC

CN4
LED 1+ - 119VDC
LED 2+ - 89VDC
LED 3+ - 60VDC
LED 4+ - 31VDC
LED 5+ - 6VDC

[CapLeaker]

Re: Hitachi LE49S508

burnt out back light leds?

[krygods]

Re: Hitachi LE49S508

can they be tested for open or short without taking apart the panel?

[CapLeaker]

Re: Hitachi LE49S508

Look at CN4. LED voltages are all over the place between the strings. The led's are bad this way or the other (shorted vs open). In order to repair that, the panel must come apart and each individual LED to be tested.

[krygods]

Re: Hitachi LE49S508

Sounds like what I was thinking. I opened the panel up last night and got through testing the first two strips of LED's, accidentally damaged one of the first few removing the lens so I'll be replacing that with one from another LED strip. Let you guys know what I discover after testing all 5 strips.

[ReeceyBurger123]

Re: Hitachi LE49S508

You can glue the lense back on woth hot glue saves replacing it, you can test each led with a Dmm.

[krygods]

Re: Hitachi LE49S508

I damaged the actual LED not the lens, the led still tests good with a DMM it just doesn't light up.

[krygods]

Re: Hitachi LE49S508

I just got finished testing all the LEDs and regluing the lenses.

All LEDs test good and light up when checked with a DMM.

Anything else that could be causing this issue?

[budm]

Re: Hitachi LE49S508

Can I see the pictures that show the wires from the LEDS that go to the LED connector?

[krygods]

Re: Hitachi LE49S508

Here's a pic of how the strips are connected and also a pic of the connector on the PSU

Let me know if you need better pics or of something else

[budm]

Re: Hitachi LE49S508

OK, so it does have 5 LED strings and they are connected in series as one big string.
Your readings at CN4 do not look right for the string #5.
CN4
LED 1+ - 119VDC
LED 2+ - 89VDC
LED 3+ - 60VDC
LED 4+ - 31VDC
LED 5+ - 6VDC

So per your readings:
String #1 has 30VDC Voltage drops (119V - 89V =30V).
String #2 has 29VDC Voltage drops (89V - 60V =29V).
String #3 has 29VDC Voltage drops (60V - 31V =29V).
String #4 has 25VDC Voltage drops (31V - 6V =25V).
String #5 has 6VDC Voltage drops, it the last string to has Cathode to GND return through current sensing resistors..
So are you sure the string #5 is OK? and those readings are valid?

[krygods]

Re: Hitachi LE49S508

I just re-checked all the LEDs in strip 5 all show a voltage drop of 841-845 and light up with the probes reversed.

I re-checked all the voltages at CN4 all remain the same as above.

When probing for voltage at CN4 the strips of LEDs light up dimly.

[budm]

Re: Hitachi LE49S508

"When probing for voltage at CN4 the strips of LEDs light up dimly.' That is good information.
So how many LEDs are there in one strip? That will tell us what the Drive Voltage at LED 1+ should be.

[krygods]

Re: Hitachi LE49S508

12 LEDs per strip

[budm]

Re: Hitachi LE49S508

12 LEDs x 5 strips = 60 LEDs, so the minimum drive Voltage should be 60 x 3Vf = 180V (or 60 x3.6Vf = 216V), so the drive Voltage of 119V is too low.
Need to look at the driver circuit next.

[budm]

Re: Hitachi LE49S508

Need good pictures of this area.

[budm]

Re: Hitachi LE49S508

OK, I trace out the connections.
Seems to me that the boost converter is not working. You should check the capacitance of that GREY rectangular cap, and get the P/N of that 8-PIN SMD IC.

[krygods]

Re: Hitachi LE49S508

Ok here is a picture of the section you want to see. Let me know if this is a clear enough picture otherwise I'll see if I can figure out how to get a clearer picture while zoomed in.

[krygods]

Re: Hitachi LE49S508

I don't have any means to test the capacitance right now, the transistor tester / esr meter that I bought from ebay isn't working properly it keeps telling me that its testing a mosfet when there is nothing being tested and tells me that every capacitor is unknown / damaged.

Here is the P/N of the 8 pin IC F28543 and below that is 083350CP

[budm]

Re: Hitachi LE49S508

Please check the resistance between LED 5+ pin and the chassis (LED connector in place) to see what you get.
Nothing come up with that IC F28543 yet.