Hitachi LE49S508

[budm]

Re: Hitachi LE49S508

What about the 5.6v on pin 6?

Since the FB pin which is the Inverting input (-) of the OPAMP has <1V, so the output will be HIGH because the NON-Inverting input (+0 is fed by the positive Voltage so you see that on pin 6 of the IC.

[budm]

Re: Hitachi LE49S508

Can I short 5v to the gate pin to see if the 119v get boosted?

No! unless you want to blow up the MOSFET and other parts by forcing on hard, it is made for switching ON and OFF at frequency.
Did you check that boost Diode (as marked in the picture I post earlier) to see if it is OK?

[danilodiaz9]

Re: Hitachi LE49S508

Yes. See post 78

[danilodiaz9]

Re: Hitachi LE49S508

When you take voltage readings across the led strings, do you read from led1+ to chassis or do you read from led1+ to led1-?

[CapLeaker]

Re: Hitachi LE49S508

The later

[mrwomp]

Re: Hitachi LE49S508

I have this same tv, It has the red standby light when you plug it in but if you power on the light goes black but nothing happens.. I was testing voltages all over following the conversation in this thread but holy smokes its crazy..

Anyways my voltages are as follows:
CON801
PS-O/F - 3.15VDC
PB adj - 3.22VDC
PB O/F - 3.12VDC
GND
GND
GND
GND
+12v - 12.29VDC
+12v - 12.29VDC
+12v - 12.29VDC

CON901
GND
KEY 0 - 3.28VDC
KEY 1 - 3.28VDC
LED G - 0.03VDC
LED R - 1.68VDC
IR IN - 5.14VDC
GND
+5V - 5.16VDC

CN4 (with tv on all are 0)
LED 1+ - 0vDC
LED 2+ - 0VDC
LED 3+ - 0VDC
LED 4+ - 0VDC
LED 5+ - 15.6VDC

I was guessing a bad LED strip, does that sound reasonable?

ETA: I get 124vdc at the booster diode.

[mrwomp]

Re: Hitachi LE49S508

So for some odd reason todays voltages changed only for the LED's.

CN4
LED 1+ - 124vDC
LED 2+ - 95VDC
LED 3+ - 66VDC
LED 4+ - 40VDC
LED 5+ - 14VDC

Could have been my DMM acting up.

[dick_barton]

Re: Hitachi LE49S508

Have you checked the voltage with the leds removed from the connector.

Reading Budm's comments in an earlier post in this thread it looks like there should be approximately 30V drop across each strip. Think I need to read further on to see what the conclusion was.

[mrwomp]

Re: Hitachi LE49S508

I have not, I will do it right now.. I have followed every other step in this thread and everything measured up to what budm said it should have been.

If I remove the connector I get 125.6vdc at led1+ but 0 on the rest. If I read it as I turn the tv on it jumps from 0 to 199vdc and after about 1 second it falls back to 125vdc again.

[dick_barton]

Re: Hitachi LE49S508

Reading through the threads the led voltage when the backlights were forced on was 204V. You have 199V with nothing connected which is quite close to the 204V.
I'm suspecting bad leds but would wait for others to verify.

[mrwomp]

Re: Hitachi LE49S508

I was thinking the same thing, I got the tv for free and I have some free time so I might just break it down and test the leds to kill some time.

[dick_barton]

Re: Hitachi LE49S508

I hope you didn't mean "I might just break it down"
Be careful when removing the panel.

[mrwomp]

Re: Hitachi LE49S508

Was pretty easy to spot the dead one as soon as I opened it up. If one led is dead it renders the rest useless, correct?

[mrwomp]

Re: Hitachi LE49S508

So I tested the one that looked dead and it was, the rest in that string worked fine..

[dick_barton]

Re: Hitachi LE49S508

You now need to check every led because you may well have more than one faulty. If one goes short circuit it puts a strain on the rest in that circuit and they start to go down like fairy lights.


https://www.youtube.com/watch?v=RxwdC7V5Ue0

[mrwomp]

Re: Hitachi LE49S508

I'm going to check them and keep the good ones in a box somewhere for future use. I wanted to use this tv for learning a bit more and I think I learned a fair bit reading and following this thread. there is no bezel on the tv, the plastics are broken, so I think I will salvage the good light strings and the boards and trash the rest.

Thanks for helping, I just needed that one "I think it may be the led" to push me to go that far.

Again thank you for the help, look forward to seeing you around the forums.

[dick_barton]

Re: Hitachi LE49S508

See you around. Cheers