Hitachi LE49S508

[danilodiaz9]

Re: Hitachi LE49S508

Where does it get boosted again? I have 119v on led#1 pin and I do have 12v to pin 1 of the led controller ic. I have 3.2v on ps on, 3.2v on pb adj, and 3.2v on bl on.

[budm]

Re: Hitachi LE49S508

Where does it get boosted again? I have 119v on led#1 pin and I do have 12v to pin 1 of the led controller ic. I have 3.2v on ps on, 3.2v on pb adj, and 3.2v on bl on.

Are we talking about the exact same board? And do you have BL-ON signal? See post 1.

[danilodiaz9]

Re: Hitachi LE49S508

Yes... same board and my bl on is 3.2

[budm]

Re: Hitachi LE49S508

Boost converter section.

[danilodiaz9]

Re: Hitachi LE49S508

So I have 119v feeding boost controller. I am reading 119v at the drain and 0v at gate and source. I have 12v on pin 1 of led controller ic but I don't see anything on pin 2 which is the gate. So I am guessing that it's not getting boosted because the circuit is being turned on. The weird thing is that I ordered a power supply of eBay for this problem which is the leds are not turning on and hence no picture. The new board has all the same readings and same problem. Is it a coincidence that they are both bad?

[budm]

Re: Hitachi LE49S508

So I have 119v feeding boost controller. I am reading 119v at the drain and 0v at gate and source. I have 12v on pin 1 of led controller ic but I don't see anything on pin 2 which is the gate. So I am guessing that it's not getting boosted because the circuit is being turned on. The weird thing is that I ordered a power supply of eBay for this problem which is the leds are not turning on and hence no picture. The new board has all the same readings and same problem. Is it a coincidence that they are both bad?

It does sound like the Gate is not being driven, you do have VCC and BL-ON to run the IC, so next thing to do is to get the spec of the IC (I did not read the whole thread again to see if we already have the spec sheet or not).

[danilodiaz9]

Re: Hitachi LE49S508

See attachments for data sheet

[budm]

Re: Hitachi LE49S508

OK, thank you for the spec sheet.
One thing you may want to verify is to have your DCV probes connected to the LED+ and put Black probe to the chassis BEFORE turning on the TV, then turn the TV on and watch and see if the Voltage on the meter jumps higher than 119VDC at first.
What may happen is that if the the LED strings has open circuit then there will be no load for the Boost converter circuit so the output Voltage will jump up real high and trip the over Voltage protection circuit (OVP) hwich is detected by PIN 7 of the IC.
You also need to look at the PWM pin 8 to see if that signal is also present or not.
See page 1 of the IC spec sheet for the Typical Application circuit.

[danilodiaz9]

Re: Hitachi LE49S508

Ok. I tried checking led+1 while powering on TV and it goes to 120v and then 119v so I don't think it's over voltage and also I do get voltage readings on all 5 led strips. On pin 8 pwm, I am getting 3v.

[budm]

Re: Hitachi LE49S508

Ok. I tried checking led+1 while powering on TV and it goes to 120v and then 119v so I don't think it's over voltage and also I do get voltage readings on all 5 led strips. On pin 8 pwm, I am getting 3v.

OK, so the circuit did not even try to start at all, well more in-depth trouble shooting will be required in that section then. You have the VCC and control signals for the circuit to run. You probably can use that application note circuit as a guide.
The LED strips are connected in series like Christmas lights. Per OP, the boosted Voltage is around 200V.

[danilodiaz9]

Re: Hitachi LE49S508

Again I just want to mention that I have tried to power supply boards with same problem. Could it then be the mainboard that is not sending the right voltages?

[budm]

Re: Hitachi LE49S508

The LED driver just need that BL-ON signal which you have indicated that you do have, and 12V at Vin pin 1, and you also have 119VDC to feed the Boost circuit.
May be something is locking it out but I do not see what that is.
Try removing the LED connector and read the L+ again when TV is turn on to see if it still showing 119V when it is first turned on.

[danilodiaz9]

Re: Hitachi LE49S508

I disconnected cable and tried again and still 120v. It does not jump higher than that. Is 3v enough voltage for the pwm? On the spec sheet it says 5v pwm. Is that just the max voltage it can accept?

[budm]

Re: Hitachi LE49S508

From spec sheet:
Dimming Control
The LED brightness is controlled by the PWM
signal at PWM pin which has different duty cycle.
OB3350 can accept an external PWM signal to
PWM pin in the range of 100Hz to 1 KHz with a
swing voltage of 0V to a level greater than 2.5V.

The signal is AC.

[danilodiaz9]

Re: Hitachi LE49S508

I am reading .7v on ovp pin and 5.6v on pin 6 which is boost converter loop compensation. This doesn't seem right. I found this image of a circuit using this ic. See attachments

[danilodiaz9]

Re: Hitachi LE49S508

Sorry here is the attachment

[budm]

Re: Hitachi LE49S508

OVP trip point per spec page 5 is 2V typ. so 0.7v is not going to trip the OVP shutdown.
OVP Protection
OB3350 shuts down the output if the output
voltage is higher than the predetermined threshold
level. In case of LED failing, the current of LED
and the resulted voltage drop on sensing resistor
is nearly zero; the converter will run at maximum
duty cycle that boosts the output voltage to a very
high level. To prevent this happen, the output
voltage is monitored through Pin OVP and
converter is shut down if the output voltage
exceeds the predetermined level. This protection
is latched and OB3350
can be reset from VIN or PWM.
BTW, I forget to ask you to check the Boost diode to make sure it is not shorted out.
This is when scope comes in handy.

Also the reading in RED as shown in the diagram does not make sense to me.

[danilodiaz9]

Re: Hitachi LE49S508

I checked the boost diode and I get 119v on both sides. With the diode checker it is around 380 while still in the circuit.

[danilodiaz9]

Re: Hitachi LE49S508

What about the 5.6v on pin 6?

[danilodiaz9]

Re: Hitachi LE49S508

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