Hitachi LE42H508

[budm]

Re: Hitachi LE42H508

Non of them should be showing any of those resistance at all.
Remove one of the Zener off the board that have all good LED and then you will see what I mean.

[Fisher77]

Re: Hitachi LE42H508

With the Zener off it measures OL.

[budm]

Re: Hitachi LE42H508

With the Zener off it measures OL.

That is correct because your meter does not put out enough Voltage to turn on the LED string.
I would remove all those Zener and test each one of them off the board.

[Fisher77]

Re: Hitachi LE42H508

Ok budm. I measured all 8 of the little buggers off the boards.

5 of them read .0
2 of the read .1
1 of them read .2
all of those readings were in both directions.

[budm]

Re: Hitachi LE42H508

Those ZENER are bad.
The LEDs strips should come on now without those Zener diodes in place.

[Fisher77]

Re: Hitachi LE42H508

Thanks budm.

I just tried them with a power supply. The ones without a blown LED light up just fine. The ones with a blown LED will not light up.

[budm]

Re: Hitachi LE42H508

Just have to replace all the bad LEDs and then the backlights should work again.

[Fisher77]

Re: Hitachi LE42H508

budm is there a good source for the LED's?
Any need to replace the Zener's?

[Andrew F. Ali]

Re: Hitachi LE42H508

Do the Zeners have any marking on them?

[Fisher77]

Re: Hitachi LE42H508

Do the Zeners have any marking on them?

They have N2 on them, and a K turned sideways.

[Fisher77]

Re: Hitachi LE42H508

Ok budm, I replaced the LED's. They are all working agin with a power supply.

Before I put this back together, do I need to replace the Zeners, or is it good to go without them?

[budm]

Re: Hitachi LE42H508

You can do without the Zener, most LED strips I repair i rarely run into one with Zener in place.
When you all finish just make sure to turn down backlights level (not brightness) to as low as you can on all input modes.
BTW, do you have the spec of the replacement LEDs? we want to make sure it is properly rated.

[Fisher77]

Re: Hitachi LE42H508

Man I hope they are right. They were listed for Hitachi.

Forward Voltage - 3.0 - 3.6v
Forward current - 265mA
Pulsed Forward Current - 330mA
Power Dissipation - 1W

[budm]

Re: Hitachi LE42H508

I expect them to be at least 300~350mA range, typical is 400mA.
Where did you get them from?

[Fisher77]

Re: Hitachi LE42H508

Ebay. Who knows if the seller had the specs listed right.
I can get more if you have a good source for them.

[Fisher77]

Re: Hitachi LE42H508

Back together and has been on for most of the day. I turned the backlights down to 25.

I appreciate all the help budm.

[budm]

Re: Hitachi LE42H508

Thanks for the follow-up on the repair.

[Fisher77]

Re: Hitachi LE42H508

Well it blew 2 more LED's. I replaced both of them and the transformer is back to buzzing.