Element 32 inches tv (ELEFW328B) Unknown component: Diode or zener?

[Vincenzo2]

My Element 32 inches tv (ELEFW328B) lost it's backlight (confirmed with a flashlight test) and the connector on the PCB (it has one board that has a processor chip, switch mode power supply, and backlight circuit) that has the two wires that go to the backlight LED strips has a very low voltage (28-29 volts) when turned ON, in my opinion.

Started testing components and found an SMD diode or zener that is shorted (even zero fusing resistors read a few tens of milliohms, while this thing reads zero).

I put some pictures here to show that it is labeled "M7". Looked up a website that is called "The ultimate SMD marking codes database" and went over all the items that came under M7 and the only two that made sense (after looking up pictures on datasheets and eleminating all the entries that should have more than two terminals) were a diode and a 24v zener diode.

I do not know which one to use.
Is there usually a zener in the backlight driving circuit?
If I remove this component and push the power button, will I get a bang and turn the tv unrepairable?
Will a power zener that is 24 volts substitute for both?

[R_J]

Re: Unknown component: Diode or zener?

It is a 1N4007 DO-214 case.
I suspect it is across the LED feedback resistors PR60~PR63 (those 2R20Ω resistors are in parallel) , that is why it measures low resistance. The led return likely connects to the diode anode and the cathode goes to ground.

Most led drive circuits use a circuit to boost the base dc voltage (29v) to a higher voltage (90v) these circuits also monitor the led current and voltage and will shut down the circuit when there is an open circuit ie: open led backlight circuit, or if the backlight plug is removed.
The main/power supply board is likely ok and you have one or more bad led's in the panel

[Vincenzo2]

Re: Unknown component: Diode or zener?

Thank you. Great information. I measured the low voltage both with LEDs connector connected and disconnected.

I just did it again. Connected to mains and off (standby), 24 volts and some change, Turned ON, 27 volts and some change and very quick jumps to 90 volts and then goes down quickly to 28v and change.

Can you give me the general LED's connection (every strip is series, or some other configuration)?
Does one bad LED turn of that protection circuit you mentioned? or does it have to be severe enough?

The diode (that you mentioned is equivalent to 1n4007) is not connected to the mosfet in any way but it does look like is in parallel to the 4 parallel 2 ohm resistors (one is actually 2.2 ohms), a connection which is weird if I want to think about an application to diode||resistor.

I was too lazy too to open all those little screws to get to the LEDs.

Thanks again

[SMDFlea]

Re: Element 32 inches tv (ELEFW328B) Unknown component: Diode or zener?

Put make and model number in thread title ! ! ! https://www.badcaps.net/forum/showthread.php?t=24661

.

[R_J]

Re: Unknown component: Diode or zener?

Thank you. Great information. I measured the low voltage both with LEDs connector connected and disconnected.

I just did it again. Connected to mains and off (standby), 24 volts and some change, Turned ON, 27 volts and some change and very quick jumps to 90 volts and then goes down quickly to 28v and change.

Can you give me the general LED's connection (every strip is series, or some other configuration)?
Does one bad LED turn of that protection circuit you mentioned? or does it have to be severe enough?

The diode (that you mentioned is equivalent to 1n4007) is not connected to the mosfet in any way but it does look like is in parallel to the 4 parallel 2 ohm resistors (one is actually 2.2 ohms), a connection which is weird if I want to think about an application to diode||resistor.

I was too lazy too to open all those little screws to get to the LEDs.

Thanks again

The led's (and the strips) in the panel are in series, so if one is open the circuit is open. The diode is across the 4 current sense resistors in the return line of the led string, not the mosfet, the mosfet source resistors are PR40,41,42 and there is no diode across them.

The voltage jumped to 90v then the circuit detected an open circuit and shut down the led drive boost voltage.

[Vincenzo2]

Re: Element 32 inches tv (ELEFW328B) Unknown component: Diode or zener?

Put make and model number in thread title ! ! ! https://www.badcaps.net/forum/showthread.php?t=24661

.

Thanks. Missed that one.

[Vincenzo2]

Re: Unknown component: Diode or zener?

The led's (and the strips) in the panel are in series, so if one is open the circuit is open. The diode is across the 4 current sense resistors in the return line of the led string, not the mosfet, the mosfet source resistors are PR40,41,42 and there is no diode across them.

The voltage jumped to 90v then the circuit detected an open circuit and shut down the led drive boost voltage.

Beautiful!
Thank you
Where do you recommend getting schematics like the one you shared?