Nexus NX3202 TV - won't turn on, power supply making noise

[Ifixstuff9]

So I just picked up a free Nexus NX3202 TV. When I plug in the TV I see the red standby LED, and when I press [power] the LED turns blue but instead of powering on the TV the power supply emits a popping sound. I attached a picture of the sound when recorded and viewed in audacity and you can see that the pulses don't follow any particular order. It sounds as if something is shorting out, and it seems to be coming from around the transformer. I highly doubt its a relay making the noise. Tomorrow I'll measure the voltages from the power supply and attach a picture of the back of the power supply board. Any idea what could be shorting out? Could it be the transformer?

[dick_barton]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

A quick initial test is to use your meter in diode mode and test the diodes and mosfets for any problems. Set powered off.

What voltages do you have on the power supply connectors and are the connectors labelled eg. 5V, 12V, GND etc.

[dskall]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

You have checked for bad connections at transformer. Maybe lift transformer and inspect bottom of transformer.

[Ifixstuff9]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

I have attached better pics of the power board. Here are the voltages:

Pin# - Pin Description - Pin Voltage standby - Pin voltage power on
1 - On - zero – 4.90v
2 - GND – GND - GND
3 - 5v - 4.93v – 4.92v
4 - Not Labeled - GND - GND
5 - Not Labeled – GND - GND
6 - Not Labeled - 0.48v – 0.46v
7 - Not Labeled - 0.48v – 0.46v

1 – Not Labeled – 0.48v – 0.46v
2 – Not Labeled – GND - GND

1 – 24v – zero – 24v
2 - 24v – zero – 24v
3 – GND – GND - GND
4 – GND – GND - GND

1 – GND – GND - GND
2 – GND – GND - GND
3 – GND – GND - GND
4 – GND – GND - GND
5 – 24v – zero – 24v
6 – 24v – zero – 24v
7 – 24v – zero – 24v
8 – 24v – zero – 24v

Everything looks fine, except for the 0.48 volts on some of the unlabeled pins, that seems suspicious. I'll check that transformer in a second.

[budm]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

https://www.badcaps.net/forum/attach...5&d=1500963234
The picture is way too small to see anything.
It looks like the main sends out the PS-ON to turn on the rest of the power supply but not the BL-ON, the Dimming control signals (the unlabeled pins).
We need the pictures of the whole backside of the TV showing all the boards also.

[Ifixstuff9]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

OK, I have some more pics. Unfortunately most of the boards a covered in shielding so they aren't visible, but I did label them so you could see which one corresponds to the pics in my first post. I also attached pictures of another board I forgot to include earlier.

[budm]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

https://www.badcaps.net/forum/attach...4&d=1501125149
If you look at that inverter board, you will see the connector has pin names for it, take the reading of each pin and report the readings, make sure to provide the pin names so we can easily find out what signals and Voltages are missing.

[Ifixstuff9]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

Here are the voltages:
VCC – zero – 24v
VCC – zero – 24v
VCC – zero – 24v
VCC – zero – 24v
NC – Not Connected
GND – GND - GND
GND – GND – GND
GND – GND – GND
GND – GND – GND
NC - Not Connected
SEL – GND -GND
E-PWM – zero – 3v
I-PWM – GND - GND
ON/OFF – zero - zero

[budm]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

OK, you do have the 24VDC to run the inverter board and you also have the E-PWM dimming control signal from the main board bit you do not have the ON/OFF (BL-ON) from the main board to turn on the inverter circuit, so something is wrong on the main board.

[Ifixstuff9]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

Hmm, so you think the noise I was hearing has nothing to do with the problem?

[budm]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

Nope.

[Ifixstuff9]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

Ok, thanks for helping me narrow it down to the mainboard. I'll start checking components.

[Ifixstuff9]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

Just made a big discovery. The unlabeled pins on the Power supply are labled on the corresponding connector on the main board, and they are supposed to supply 12 volts. That means there is an issue with the 12 volt rail because it is only supplying .48v.

[dick_barton]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

Have you checked the 12V line with the set off with your meter on ohms to see if there's a short or very low resistance on any of them.

[R_J]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

It looks like the two transformers (12&24 volt) primaries are connected together, so If you have 24volts, check the dual diode for the 12 volts, and that (resistor/jumper wire?) and coil between diode and output connector.

[Ifixstuff9]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

I measured the voltage coming from the output pin of the dual diode that supplies power to the 12v line and it is fluctuating around 100mv, although I still have a steady .46v on the 12v line but that's probably because of all the capacitors.

The other pins of the dual diode each connect directly to separate transformers. So my question is, do you think the dual diode is bad or could the problem be with the transformers? The dual diode for the 24v rail is connected to the same transformers and its working fine so I'm leaning towards a bad dual diode.

[dick_barton]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

Remove the diode and test out of circuit. What's the part number of the diode.

[R_J]

Re: Nexus NX3202 TV - won't turn on, power supply making noise

Check the resistance of the transformer secondary to make sure its not open, to check the primary you would need to isolate at least one of the pins from the the trace as the 24 volt primary is connected in parallel with the 12 volt primary

It looks like they take one winding from each transformer secondary to supply one side of the dual diode, so I would think if there is 24 volts, 12 should also be there unless the diode is open or the + 12 has a short at its output
I would check the dual diode on the 24 volt side also, half of it could be bad?