sharp lc-42ad5e-bk No power No standby led

[elchatarreroelectronico]

Hello to everyone, and first of all sorry for my English, I'm new here and mostly all the TV's that I had repaired was due to bad capacitors, but this one It's different

Well, I think I almost read all the post related to the Sharp Aquos, but there are slight differences to my TV and I'm a bit confused, diferent type of power supply, different pins names, ….etc.....

I'm using this manual LC-42AD5E/RU/S from elektrotanya, here the link: http://elektrotanya.com/sharp_lc-42a.../download.html , It seems exactly the same for my tv except for the IR board, that has differnet number of pins.

Well, let's move to the problem:

The TV is totally dead ( no standby/no power)

Here is what I tested (No changes when I press the power on/off switch in all readings):

POWER SUPPLY READINGS

Main capacitor: 319V

PA conector:

BU5V: 5.056V
UR5V: 5.057V
UR13V: 0V
UR35V: First 18V and go down

PB conector:

PCON1: 0V
PCON2: 0V
INV_ON: OV
INV_BRT: 0V
POWER_DET: First 0.3V and go down
FAN_ERR: 0.062V
LCD_POW: 0.066V
SEL: 0V

LA conector:

INV24V: 0V
INV_ON: 0V
INV_BRT: 0V
SEL: 0V

LD conector:

INV24V: 0V


MAIN BOARD READINGS (Digital board disconected) :

BU1.8V : 1.8V
BU3.3V: 3.3V
BU+5V: 5V
+3.3V: 0.012V
P+35: 0V
S+8V: 0V
BU+12V: 0V

Well so it seems to me that is a problem with the Main board. So I have some questions to keep trobleshooting:

How can I send the on signal to the main board to check the inverter?
Should I use 5V or 3.3V voltages to short the signal to ground and start the inverter?
What pins should I use? INV_ON, PCON1,PCON2 ?.........

There is a troubleshooting guide in the service manual, It says that the condenser C7800 has to be charged to 400V (mine 319 V).I jumped some steps due I find de 5V output.

So.......What do you think? Should I go step by step cheking all the trobleshoooting diagram says?
Do you have any advise to look for?
Can you guide me?

Thanks a lot.

P.D. I forgotten my camera with the pictures for the tv, tomorrow I should uploaded it, If you need more info please tell me.

[elchatarreroelectronico]

Re: sharp lc-42ad5e-bk No power No standby led

I forgot all caps seems to be ok

[budm]

Re: sharp lc-42ad5e-bk No power No standby led

I did not look at the service manual yet, but from what I can see, the standby power supplies are working is not sending the control signals (PCON1, PCON2) to the power supply board to turn on the 24V power supply to run the inverter board, it is also not send inverter on signal to turn on the Inverter, and also no Dimming (invr brt) control signal either.
You can try disconnecting the T-CON board to see if the TV will response, at this point it looks like you do have main board problem.
Please upload the pictures of the boards and the whole backside of the TV.
BTW, if this TV uses ACTIVE HIGH signal then when the on command voltage will be = >2.5VDC = ON, < 1VDC = OFF.

BTW, the DC voltage on the main filter is on the low side, it should be around 325-330VDC if your line voltage is 230VAC.

[elchatarreroelectronico]

Re: sharp lc-42ad5e-bk No power No standby led

Thank's for the quick response budm

I had already read those documents that you had posted.

Today I'll try to disconnect the TCON board and see what happens.

In case that It doesn't work. How can I force the psu? Should I short Pcon1,Pcon2,Inv_on, to 3.3V or 5v?

Well here are the photos and some schematics I'm using. If you need more detail photos tell me please.

Thanks a lot.

[elchatarreroelectronico]

Re: sharp lc-42ad5e-bk No power No standby led

And here are some of the schematics that I'm using

Today I'm gonna try to disconnect the TCON and take some hi res photos.

Thanks

[budm]

Re: sharp lc-42ad5e-bk No power No standby led

"In case that It doesn't work. How can I force the psu? Should I short Pcon1,Pcon2,Inv_on, to 3.3V or 5v?" I would use two 100~500 Ohms between the 5V and the PCON 1, 5V and PCON2 to force on the power supply, as you can see you just need to turn on those two transistors which will turn on the two opto-isolators.
So force the power supply and see if you do get the 24V to run the inverter, then you can use another resistor to force on the Inverter, do not force on the power supply and the inverter on at the same time, you must turn on the power supply first and then turn on the inverter.

[elchatarreroelectronico]

Re: sharp lc-42ad5e-bk No power No standby led

Thanks so much for the quick response !!!!

I'll try that too, and tell you what happens!! So a good test afternoon in the lab today!!

Yeah!!!

[elchatarreroelectronico]

Re: sharp lc-42ad5e-bk No power No standby led

OOpsssss I forgot, all the tests with or without the mainboard?

[budm]

Re: sharp lc-42ad5e-bk No power No standby led

OOpsssss I forgot, all the tests with or without the mainboard?

That is correct, we just want to make sure we can force on the power supply, beside if you have main board connected, those signal line will be kept low by the main board due to the transistors (used as switch) on the main board are on to keep the line low and they will be damaged if we do not disconnect the cables between the main board and the power supply board when we do force on method without resistors and cables connected.
When you force on m you should see the voltage on the main filter cap C7800 goes up from 325VDC (measure right at the two legs of the cap) to >360VDC (Due to the PFC Voltage booster kicks on).

[elchatarreroelectronico]

Re: sharp lc-42ad5e-bk No power No standby led

First of all, Thanks so much for your help!!!!

Here is the story, I hope someone helps it.

Yesterday I test to disconnect the T-CON board then, I plug the mains cable and I tried to power it , I realize the standby led blinks red once C7001=0V.

Try again while C7001 was discharging and no blink.

I waited until C7001=0V an tried again, power and no blink, I tested the voltages and no change, so I moved on and tried to force the psu like you said.

I disconnected all the main board connections.

I used three 220 ohm resistor for each signal P-CON1, PCON-2 and INV_ON; I soldered them to 5V and left one lead for shorting INV_ON later.

Time to start to pray.........

Plug de mains cord and...........It powered on!!!!!!! , all the ccfl and without touching the INV_ON ( Is that normal? Should I shorted INV_ON if the ccfl was working?)

Here the voltages readings: (without shorting INV_ON)

PA:
BU5V: 5.08V DC
UR5V: 5.1V DC
UR13V: 12.2V DC
UR35V: 32.5V DC

LA:
INV24V: 19VAC


Note: I think this Is the hardest part due this aren't cable conectors, are exposed ones, and it has corrosion on it so a lot of false readings, and also due it are exposed ones is very easily to make a short; indeed I made one between UR35V and GND and I was using the thinnest probe that I have with a shrinking tube exposing only the tip. Well I inmeddiatly swith it off and later on, and continues working. It's possibly that I burned something? Some tech tip to make measuremnt in that kind of cables?


So....... It seems that I have to change my mainboard. Isn't it? Any advice about it? Or only I have to buy one with the same serial numebr and plug-it?

I'll upload some photos of the process, so maybe It helps someone.

[elchatarreroelectronico]

Re: sharp lc-42ad5e-bk No power No standby led

Sorry Cap numer 7800

[budm]

Re: sharp lc-42ad5e-bk No power No standby led

At this point we know for sure that the main board is not sending the PCOns command to turn on the power supply.
You should monitor the PCON1 and 2 with the meter to see if they spike up for seconds or not when the power switch is activated.

"INV24V: 19VAC" are you sure it is 19VAC?

Here is the simplified POWER-DET circuit, it is made to see if the switched +24V for the inverter circuit is working or not (or if the Voltage is below 16V).

When Pcon1 is HIGH (PCON2 is also HIGH) Q7311, Q7310, Q7202 (Notes: the pull up resistor to the Collector of Q7202 is on the main board) are on, when the 24V power supply comes on, Q7201 will turn on which will turn OFF Q7202 and causes Collector Voltage of Q7202 to be HIGH (normal condition), if the 24V fail to come on the POWER-DET signal will be LO then the main board will shutdown and reports the fault.

[elchatarreroelectronico]

Re: sharp lc-42ad5e-bk No power No standby led

Thanks soo much.

I have so much to learn.........

I'm going right now and check PCON1 and PCON2, so I have to disconnect the resistors and plug in all connector and check if is there any spikeup. Isn't It?

About the INV24V I'm not sure 100% I'll will check it too.

About the Power-det circuit, I think I forgot a lot of the electronics that I have learnt some year ago , thanks so much for the effort, I'll study it. So Have I to monitor de POWER_DET circuit too? or Are the schematics you made only for help me out with the understand the function?

[budm]

Re: sharp lc-42ad5e-bk No power No standby led

"I'm going right now and check PCON1 and PCON2, so I have to disconnect the resistors and plug in all connector and check if is there any spikeup. Isn't It?" that is correct.
So Have I to monitor de POWER_DET circuit too? yes, but the main key is that the 24V must be there otherwise the POWER-DET fault will kick in.

[elchatarreroelectronico]

Re: sharp lc-42ad5e-bk No power No standby led

Right now testing INV24V

I`m just realized of this: (I've tested with two multimeters)

Multimeter Black and Red probe connected:

INV24V: 19,60 VAC 0VDC

If I disconnect the Black probe "GND" the volages are the same!! False reading, I asume that the multimeters are picking noise from the ccfl.

So........I dont know what to do...

[elchatarreroelectronico]

Re: sharp lc-42ad5e-bk No power No standby led

Please hit me!! I know right now that my problem is about the false readings,. I disconnect all and start for the begining, put the psu in the workbench (This time upside down "Of course" newbie stupidity!!! i was making the readings from the components side ) and take all the measurements (more than twice this time) in the same condition Pcon1,pcon2 to 5V no INV_ON connected, and this time y move the black probe straight to GND plane in the pcb

Here the readings:

PC con:
S24V= 22.38VDC no AC

PA con:
UR35V: 36.37VDC
UR13V: 12.3VDC
UR5V: 5.055DC
BU5V: 5.055DC

PB con:
P-CON1: 4.515VDC due to resistor
P-CON2: IDEM
INV-ON: 5.064Vdc without resistor
INV-BRT: 3.359Vdc
POWER_DET: 1.5Vdc and going down to cero
FAN_ERR: 0Vdc
LCD_POW: 0Vdc
SEL: 3.98Vdc

So the big cuestion. I think I have to solder diferents cables to the pcb in order to make reliable readings and check the spike up in the CON signals.

Am I correct? What do you think?

Until tomoroww can't keep testing.....

P.D. I'm sure about the picking noise phenomenon

[selldoor]

Re: sharp lc-42ad5e-bk No power No standby led

So were the back lights connected and did they come on?

[elchatarreroelectronico]

Re: sharp lc-42ad5e-bk No power No standby led

yes

[elchatarreroelectronico]

Re: sharp lc-42ad5e-bk No power No standby led

They were always on

[budm]

Re: sharp lc-42ad5e-bk No power No standby led

"INV-ON: 5.064Vdc without resistor" That means the Inverter circuit has pull-up resistor in place already that is why the backlights come on when 24V is present without using force on resistor for the backlights.
I would say that your power supply board is OK.