Dynex dx-22ld150a11 LCD TV No Power Dead

[arman960]

totally dead. When I push the power button ,nothing happens. No light. No sign of power.

I checked the fuse on power board. Fuse is ok. I checked the resistance of the transformer pins S1 & S2 =972 Ohm
S3 & S4 =972 Ohm


Whoever replies thanks for that.

[budm]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

Do you have about 165vdc on that large brown cap?
Any 5vstby?
Also good pictures of this power supply/inverter board both sides and also good closed up in 1/4 section each so I can trace the copper tracks

[arman960]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

Do you have about 165vdc on that large brown cap?
Any 5vstby?
Also good pictures of this power supply/inverter board both sides and also good closed up in 1/4 section each so I can trace the copper tracks

I get 172.4 VDC from that big brown caps.

[ben7]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

I get 172.4 VDC from that big brown caps.

That is good. Infact, your line voltage seems a bit high. But it's not dangerously so.

Does the white transformer make a ticking sound when you try to turn it on?

[arman960]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

There is no sound or clicking noise. No LED anywhere. when I push the power button, nothing happens.

This main board is connected to DVD player. This TV basically has powerboard integrated with Inverter and main board. Basically two boards and dvd player

[budm]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

As you can see in picture #3 in your post #1, see if the you have 5V on that pin (pin #3 from the right).

[arman960]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

There is no 5 volts or 12 volts. The unit is dead.

It has one section primary and other section secondary.

[ben7]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

There is no 5 volts or 12 volts. The unit is dead.

It has one section primary and other section secondary.

The smps IC is an SG6742MR

Check the voltage:

1. From GND to pin 4 (Vstart)
2. From GND to pin 6 (VDD)

Please report back your findings.

[arman960]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

The smps IC is an SG6742MR

Check the voltage:

1. From GND to pin 4 (Vstart)
2. From GND to pin 6 (VDD)

Please report back your findings.

GND to PIN 4 = 8.2 VDC


do you think the IC is bad?

GND to PIN 6 = 0 VDC

[lti]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

VDD is pin 7, not pin 6.

The voltage on pin 4 seems low. I would check the components connected to pin 4 and the resistance from pin 4 to ground, but someone else might have a better idea.

[arman960]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

VDD is pin 7, not pin 6.

I get 0 vdc from 6 and 7 pins.

[budm]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

When HV is applied to pin 4, the DC voltage at pin7 VDD should start rising, when it reaches the VDD-ON (15.5V), the Gate drive signal will appear at pin8 Gate drive to drive the MOSFET, when the drive happens the DC will be generate by the rectifier diode that is connected to the Aux winding of the standby switching transformer which will keep itself running and the IC will no longer use the HV voltage. Since pin4 is reading only about 8V, that will not be enough to start up the IC. If you look at the app note, the circuits used in your TV will be really close to what is shown.
So take the resistance reading at pin4 as suggested by lti, also take the resistance reading at pin 7 also. Check the resistor and cap that supplies the power to pin4 also.

[arman960]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

When HV is applied to pin 4, the DC voltage at pin7 VDD should start rising, when it reaches the VDD-ON (15.5V), the Gate drive signal will appear at pin8 Gate drive to drive the MOSFET, when the drive happens the DC will be generate by the rectifier diode that is connected to the Aux winding of the standby switching transformer which will keep itself running and the IC will no longer use the HV voltage. Since pin4 is reading only about 8V, that will not be enough to start up the IC. If you look at the app note, the circuits used in your TV will be really close to what is shown.
So take the resistance reading at pin4 as suggested by lti, also take the resistance reading at pin 7 also. Check the resistor and cap that supplies the power to pin4 also.

I do not have Multimeter to measure capacitance. So I just use multimeter's Mega Ohm to see if the capacitor charging or not. But I can check those capacitor and ressitors that supplies power to pin 4.

when you said to measure resistance at pin 4 and 7, did you mean resistance between pin GND and pin 4?

[ben7]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

Sorry about the pin messup.

I think, the chip could be bad - but first you should measure the resistance of pin 7 (from pin 7 to ground). Make sure the board is unplugged and the giant filter capacitor is discharged first!

[budm]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

Sorry for not being clear:
4 and Gnd, 7 and Gnd.
Does the app notes circuit match pretty close to your board?

[arman960]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

Sorry for not being clear:
4 and Gnd, 7 and Gnd.
Does the app notes circuit match pretty close to your board?

Yes the circuit close to the IC looks like this. But I am not good at reading the trace circuit diagram though. The pictures are in Primary power supply section

The resistance between 4 and GND is open

resistance between 7 and GND is only 3.5 Ohm

is this normal?

[budm]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

That is NOT normal at all on pin7. You will have to carefully unsolder and lift pin7, then take the reading again.
Can you take good clear pictures of the board in the IC area so I can see how the traces are connected? Pin 7 looks like it is connected to a jumper wire.

[arman960]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

That is NOT normal at all on pin7. You will have to carefully unsolder and lift pin7, then take the reading again.
Can you take good clear pictures of the board in the IC area so I can see how the traces are connected? Pin 7 looks like it is connected to a jumper wire.

Here is the picture of top bottom and lower section of the board

[budm]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

OK, much better pictures with less reflection.
Correction! I look real close at the picture, pin 7 is connected to J7 jumper, and it is ALSO connected to C104 to ground and also ZD101 to ground.
So best thing to do is to lift pin 7 off the board.
So the short can be the IC, C104, or ZD101.

[arman960]

Re: Dynex dx-22ld150a11 LCD TV No Power Dead

OK, much better pictures with less reflection.
Correction! I look real close at the picture, pin 7 is connected to J7 jumper, and it is ALSO connected to C104 to ground and also ZD101 to ground.
So best thing to do is to lift pin 7 off the board.
So the short can be the IC, C104, or ZD101.

Ok removed the J7 jumper and than measured the resistance.

GND and pin 4= open or very high resistance (above 2M Ohm)

GND and 7= 3.5 Ohm