DYNEX 40" Model DX-L40-10A/4832 Will not power on.

[budm]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

Put all the old board back in place and report the Voltage readings as shown in post 1, 9.
We need to find out what signals and Voltages are missing first.

[evelhorn]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

OK things got weirder, was checking the voltage levels on the dx-l40-10a I've been attempting to fix and as I was waving my multimeter over the high voltage side of he board it made an odd sound and started working. Or at least it works while its laying flat, once I turn it upright it goes dead, not even the red standby light is on. I can find no loose connections or anything like that so I would greatly appreciate any insight. Has anyone else seen this happen

And on a side note, thanks budm for always replying to my noob posts

[CapLeaker]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

resolder the transformers, all transistors and diodes mounted on the heat sink, basically everything that get's hot. Maybe you have a cracked solder joint.

[evelhorn]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

I'll check, I've got one of those magnifying glasses you see at the dentist office. Its huge and self lit. But some how I think its something else

[evelhorn]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

Found the culprit, it was the cable connecting the power board with the main board. If it moved in any way it killed the power. I anchored it securely and it works fine now. I'll order the cable once I find it, no luck so far, it plays fine for now and it's not like I'm gonna move it around. Thanks for everyone's input

[CapLeaker]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

Thanks for the feedback!

[tomandrews86]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

I have a TV with the same symptoms and is testing identically to that of the original poster. I have not had any luck finding cold solder joints, I replaced C811,812,814 as one poster had found they had gone high ESR and was causing similar symptoms. There has been suggestion that the likely culprit is C842 (the 2000V 22nF). As I am the curious type and don't happen to have one of these on hand, before ordering one, can someone explain what the purpose of this cap is and why its failure would cause such symptoms?

[budm]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

That is the DC Blocker/ coupling cap for driving the power transformer.

[tomandrews86]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

If it was bad would I be getting the voltages I am? They all appear normal do they not? (Mine are same as in original posting only my 12v is 11.8V not 12.8V as he is getting)

[budm]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

How about the 24V output?
You should report all the VDC readings of all those white connectors in the secondary side with the name of each pins next to the reading.

[tomandrews86]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

From top to bottom along the right side of the board are three connectors.
The multicolored connector going off to inverter board. (Top to bottom)
Unlabeled - Yw - 0.823V
Unlabeled - Or - 4.06V
Unlabeled - Red - 58.7mV
Unlabeled - Br - 0V
Gnd - Bk - 0V
Gnd - Wh - 0V
Gnd - Gy - 0V
Gnd - Pu - 0V
Gnd - Bu - 0V
24V - Gr - 24.76V
24V - Yw - 24.76V
24V - Or - 24.76V
24V - Red - 24.76V
24V - Br - 24.76V

Below that is a 14pin connector going to main board:
GND - 0V
GND - 0V
STB - 2.895V
5V_S - 4.93V
5V_S - 4.93V
12V - 11.80V
12V - 11.80V
GND - 0V
BR1 - 4.05V
SW - 59.3mV
GND -0V
GND -0V
5V_M - 5.22V
5V_M - 5.22V

At the very bottom right is a 4pin connector going to main board:
4 - GND - 0v
3 - GND - 0V
2 - 16V - 16.36V
1 - 16V - 16.36V

That should be all of them. I've got the TV open and my meter on hand if I missed any.

[budm]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

From top to bottom along the right side of the board are three connectors.
The multicolored connector going off to inverter board. (Top to bottom)
Unlabeled - Yw - 0.823V
Unlabeled - Or - 4.06V
Unlabeled - Red - 58.7mV
Unlabeled - Br - 0V
Gnd - Bk - 0V
Gnd - Wh - 0V
Gnd - Gy - 0V
Gnd - Pu - 0V
Gnd - Bu - 0V
24V - Gr - 24.76V
24V - Yw - 24.76V
24V - Or - 24.76V
24V - Red - 24.76V
24V - Br - 24.76V

Below that is a 14pin connector going to main board:
GND - 0V
GND - 0V
STB - 2.895V
5V_S - 4.93V
5V_S - 4.93V
12V - 11.80V
12V - 11.80V
GND - 0V
BR1 - 4.05V
SW - 59.3mV
GND -0V
GND -0V
5V_M - 5.22V
5V_M - 5.22V

At the very bottom right is a 4pin connector going to main board:
4 - GND - 0v
3 - GND - 0V
2 - 16V - 16.36V
1 - 16V - 16.36V

That should be all of them. I've got the TV open and my meter on hand if I missed any.

OK all your power supply Voltage are OK, but the main board is not sending the BL-ON (SW) to turn on the backlights, that SW pin should be >2.5VDC to turn on the backlights.

[tomandrews86]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

Thanks for your response. Now that I know the main board is not sending the BL-ON to the backlights what should I look into next? I've checked all of the voltage regulators on the main board (except N4 which I cannot locate and I suspect is under the shield) and compared them to the service manual - they are all working.

[budm]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

You are going to trace out the connection from the PS-ON (SW) pin on the main board to find out where it goes to which will be the hardest part, the PS-ON signal is controlled by a switched transistor, and that switched transistor is command to on or to be off by the processor.
Without diagram, you can spend lots of time tracing out the circuits.

[tomandrews86]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

It would appear that I have lucked out and the service manual contains the following schematic which shows the the pin connected to the SW pin of the connector back to the uprocessor. I will probe it out with my meter tomorrow and report what I find.

[budm]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

Transistors V1 and V2 are simple inverter circuits.
When TV is off V2 is ON (PS-ON = LO), V1 is OFF and when the power switch is activated, the processor output goes HI (ACTIVE HI) V1 is turned on, V2 is turn OFF = PS-ON HI.
So check the V1's Veb Voltage to see if goes to 0.6VDC when power switch is activated.

[tomandrews86]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

I had a chance to take a look at it again this morning. I am never getting any Veb on V1 when I press the power button. My TV does not have all of the components that were in the original schematic I posted, some components were simply omitted (the silk screening and pads are still present). I've edited the schematic to show what is in my TV.

What's next? I know I'm not getting that power on signal from the processor, what conditions need to be met before the processor will send out that signal? Is it simply pressing the power button that does it or does the processor check for certain conditions before sending that signal? Or is this where you throw in and just say the main board needs replacement?

[budm]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

Is V2 present? Check V2 Vbe to see if it toggle.

[tomandrews86]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

V2 is not present. I have marked up the schematic to show what is there. (it's attached to my last post)

[budm]

Re: DYNEX 40" Model DX-L40-10A/4832 Will not power on.

I am sorry typo. If the processor output does not change state then there is not much you can do.