Element ELCHW402 - Screen Does Not Turn On

[jjl4999]

Hello,

I would appreciate the help troubelshooting Element ELCHW402 screen not turning on. The red power indication LED is lit.

I have read the forums for the past few weeks and performed some troubleshooting. Great information but I couldn't solve the problem.

I've tested the power board with control board plugged in and received the following results:

STB: 2.12V
5V_S (#1): 4.79
5V_S (#2): 4.79
12V (#1): 0
12V (#2): 0
BR1: 0
5V_M (#1): 0
5V_M (#2): 0

I also noticed that STB does not drop < 1V when I press the physical power button or when I used the remote's power button. I tested the power button signal back to the main board and recorded a voltage drop from 3.3V to 1.8 when it is pressed which seems to indicate a signal is reaching the main board.

Thanks in advance for any time or help provided. All suggestions and ideas are welcome. I've attached pictures of the boards. Some of the photos overlap each other but I wanted to make sure I provided as much visual assistance.

[dskall]

Re: Element ELCHW402 - Screen Does Not Turn On

With main board unplugged from power board what voltages do you get on connector

[jjl4999]

Re: Element ELCHW402 - Screen Does Not Turn On

Hi Dskall. Thanks for the response.

STB:0
5V_S (#1): 4.81
5V_S (#2): 4.81
12V (#1): 0
12V (#2): 0
BR1: 0
5V_M (#1): 0
5V_M (#2): 0

[dskall]

Re: Element ELCHW402 - Screen Does Not Turn On

With about a 1k resistor between STB and 5_S with main unplugged what readings do you have

[R_J]

Re: Element ELCHW402 - Screen Does Not Turn On

I see kits available for this power supply so it is possible it has a problem, here is the schematic.
This schematic is for 240 vac input so instead of 300vdc accross c808 you should have 160 vdc with 120 vac input
Do what dskall suggests, you should here the relay click, and get your +12 volts. If not check the DC voltage accross C808, next check the voltage accross C810 (PFC)

[jjl4999]

Re: Element ELCHW402 - Screen Does Not Turn On

With about a 1k resistor between STB and 5_S with main unplugged what readings do you have

1 k resistor between STB and 5V_S
STB = 2.7 V
5V_S = 4.8 V
5V_S = 4.8 V
12V = 0
12V = 0
5V_M = 0
5V_M = 0

[jjl4999]

Re: Element ELCHW402 - Screen Does Not Turn On

I see kits available for this power supply so it is possible it has a problem, here is the schematic.
This schematic is for 240 vac input so instead of 300vdc accross c808 you should have 160 vdc with 120 vac input
Do what dskall suggests, you should here the relay click, and get your +12 volts. If not check the DC voltage accross C808, next check the voltage accross C810 (PFC)

Thanks for the post RJ.

The relay does click when I plug it but I do not get the 12 V. With 1K resistor still between STB and 5V_S:
C810 = 220 VDC
C808 = 140 VDC

[budm]

Re: Element ELCHW402 - Screen Does Not Turn On

I do not see c810 (220uf 450vdc) on that power supply board. The biggest filter cap on that board is that I see is C810 390uf 250vdc CAP. 120V version uses only 250VDC rating cap then? May be that is why the PFC Voltage as measured is only 220VDC and it is working.

[R_J]

Re: Element ELCHW402 - Screen Does Not Turn On

The next voltages I would check are on IC N831, Does it have VCC (around 12 volts?) on pin 12 and is there voltage on pin 16 (around 10 volts)
Since its a smd ic I would check the voltage on anode and cathode of VD831 and then + side of C838
I'm starting to think it could be an open C842, but that make of cap does'nt look like the ones that usually bulge and go open (square white ones)
Looks like your meter might be reading a bit low

[jjl4999]

Re: Element ELCHW402 - Screen Does Not Turn On

The next voltages I would check are on IC N831, Does it have VCC (around 12 volts?) on pin 12 and is there voltage on pin 16 (around 10 volts)
Since its a smd ic I would check the voltage on anode and cathode of VD831 and then + side of C838
I'm starting to think it could be an open C842, but that make of cap does'nt look like the ones that usually bulge and go open (square white ones)
Looks like your meter might be reading a bit low

The meter may be running low. It isn't a high end meter, TackLife Brand.

I plugged all of the boards back in to take measurements below:

N831
Pin 12: 61V
Pin 16: 0 V

VD831
Anode: 61V
Cathode: 0V

C838 Plus Side: 61 V

C842 - I originally thought it was that capacitor as it seems to be a common failure. It measures approximately 51 nF in circuit.

Thanks again for the help. I can't figure out why Pin 12 has 61 V.

After taking the readings, I attempted to double check the numbers and now the relay won't stay in for more than 2 or 3 seconds before clicking open.

[dskall]

Re: Element ELCHW402 - Screen Does Not Turn On

For clarification on power board you have a side marked hot and a side marked cold with lines around each. All measurements on hot side. The ground reference point will be neg. of your main filter cap. For cold and all others the ground will be chassis.

[R_J]

Re: Element ELCHW402 - Screen Does Not Turn On

When you make the measurements on the hot side, you need to use the right ground, Use the negative side of C810 and not the metal chassis.
Hot ground is shown like a triangle or triangle made with lines, Cold ground or secondary looks like this ///

[jjl4999]

Re: Element ELCHW402 - Screen Does Not Turn On

BUDM / RJ - Thanks for the knowledge and advice. The following readings use the negative side of C810 as reference:
N831
Pin 12: 8V
Pin 16: 8V

VD831
Anode: 8V
Cathode: 8V

C838 Plus Side: 8 V

[R_J]

Re: Element ELCHW402 - Screen Does Not Turn On

It seems the vcc is too low, that voltage comes from VD813,814 so check those 2 diodes and check the 2 caps C811, C812. So its either the pfc circuit (N811) can't supply the voltage or something is loading down the vcc (shorted/leaky VZ831), bad N831 ?

[jjl4999]

Re: Element ELCHW402 - Screen Does Not Turn On

I measured the devices in question and measured:
C812: 16 uF in circuit. Discharged capacitor and read resistance. Capacitor read ohms for a second or two then reads open.
C811: 16uF in circuit. Discharged capacitor and read resistance. Capacitor read ohms for a second or two then reads open.
VZ831: meter in diode mode. Forward voltage: .53V
Reverse voltage: 2.7V
VD814: meter in diode mode. Forward voltage: .53V
Reverse voltage: 2.8V
VD813: meter in diode mode. Forward voltage: .52V
Reverse voltage: 2.8V

Would you recommend other tests to verify these components? If not, I guess my next step is to replace ICs?

[R_J]

Re: Element ELCHW402 - Screen Does Not Turn On

I guess you could check the voltage on vz812 (ic N811 pin 8) it could be between 12 & 18 volts, It seems strange that the VCC point for N831 (anode of vd831) is 8 volts and pin 16 and 12 are also 8 volts, that says there is no voltage drop accross vd831/R842 or R843, so I suspect its not getting supplied enough voltage to start up.
so even though the pfc seems to be working giving 220 volts accross C810 it may not be enough, and if its low VCC supplied by VD813/814 would also be low.
and the circle continues...

[budm]

Re: Element ELCHW402 - Screen Does Not Turn On

I think the PFC of 220VDC is OK since the cap C810 is only rated at 250VDC.

[dick_barton]

Re: Element ELCHW402 - Screen Does Not Turn On

As BudM says the 220V looks to be OK considering the rating of the main capacitor.
It definitely looks as thought VCC supply is not correct and should be a few volts higher since at 8V it appears to be below the minimum operating voltage of N831

I would change out C811 and C812 to start off.

[jjl4999]

Re: Element ELCHW402 - Screen Does Not Turn On

Thanks Dick. I plan to go by an electronic shop and pick up some replacement capacitors. I'll replace and post results tomorrow.

[jjl4999]

Re: Element ELCHW402 - Screen Does Not Turn On

I purchased two like kind replacement capacitors and recorded the following results:
C812 measured 4.48 uF out of circuit.
C811 measured 4.75 uF out of circuit.
Both new capacitors measured 11 uF out of circuit.

I installed the new capacitors at C811 and C812 and first plugged the 1K resistor connecting Standby and 5Vs. I was able to measure around 13V on N811 pin 12 and around 10 V on N811 pin 12, all referenced to negative of C810. Voltages were in the acceptable range listed in Dick's document. I then connected all of the boards to the main power board, pressed the TV Power button, and recorded the following results at the cold side connector when referenced to the chassis:
STB: 2.16 V
5V_S (#1): 4.94 V
5V_S (#2): 4.94 V
12V (#1): 11.99 V
12V (#2): 11.99 V
BR1: 2.84 V
5V_M (#1): 5.27 V
5V_M (#2): 5.27 V
SW: 3.02

These values seemed normal so I picked up the TV and saw the blue screen with no signal message. I connected an antennae and have the TV powered on and working for the past few hours.

Thanks to everyone for the knowledge and information. I enjoyed the whole process. My first successful electronics repair.

I have to admit that I would not have guessed changing out C811 and C812 would have solved the issue. Any tips on how to become better at troubleshooting power boards and following schematics?