Sharp LCD 32DH57E No power up.

[Techstar]

I have this sharp 32 inch LCD TV that appears to be stuck in standby.
When I plug the set into the mains there is no led lit , when I press the on off button on the TV the LED turns red but the tv remains lifeless. There is no remote control function.
at all. The 12 .5 volt rail is only measuring 7.8 volts , PS ON seems to be stuck at 0.2 v. I notice the voltage on the Mains Filter Cap is 343v - 345v slightly fluctuating not a rock steady reading , I am wondering if the PFC is working right.
Connector P7202 Measurements.
PIN 1 - 0V
PIN 2 - 0V
PIN 3 - 0V
PIN 4 - 0V
PIN 5 - 0.2 V
PIN 6 - 0.2V
PIN 7 - 0V
PIN 8 - 0V
PIN 9 - 0V
PIN 10- 0V
PIN 11- 7.8V
PIN 12- 7.8V
PIN 13- 7.8V
PIN 14 7.8 V
https://www.manualslib.com/manual/11...age=105#manual

[dskall]

Re: Sharp LCD 32DH57E No power up.

Don't know what voltages should be on pins. You say 7.8v on 12v. What is it when unplugged from main?

[Techstar]

Re: Sharp LCD 32DH57E No power up.

The voltage is the same 7.8 v, no difference if the main board is plugged in or not. click the link in my first post to see how the circuit works.

[dskall]

Re: Sharp LCD 32DH57E No power up.

You will probably not get any pfc until you get ps-on. You may not be getting ps-on with 7.8v. Maybe bad optocoupler or ic7201 parts around it.

[Techstar]

Re: Sharp LCD 32DH57E No power up.

Thanks for the help

[attainteddragon]

Re: Sharp LCD 32DH57E No power up.

pin 4 0v
this is your stby pin. you need to recover this voltage before you go chasing your secondary voltages.

someone with more knowledge will need to jump in, as i couldn't see where stby is transported to this pin.

[budm]

Re: Sharp LCD 32DH57E No power up.

This power supply ony has one power supply so when it is in standby mode, the output Voltage is set (by controlling the Vref diode IC7202 KIA431, and the ADJ pin of the SMPS IC) to put out lower Voltage, 7.8V, enough to run the main board, when the PS-ON is present then 12V pin will put out 12V, and the PFC Booster circuit will also come on. So you need to get the main board to send out the PS-ON to turn the power supply fully on.
Connector P7202 Pin 6 is the PS-ON pin, you can try forcing on the power supply board by itself to see if the 12VDC and the 60VDC will be present or not.

[Techstar]

Re: Sharp LCD 32DH57E No power up.

I have forced the Power Supply board on here are the voltage readings
on connector P7202
Pin 1= 0v.
Pin 2= 0v.
Pin 3= 0v.
Pin 4= 0v.
Pin 5 0.2.
Pin 6= PS on = forced on with 2.3 volts.
Pin 7= 0v.
PIN 8= 0V.
Pin 9 = 0v.
Pin 10 = 0v.
Pin 11 =12.5v.
Pin 12= 12.5v.
Pin 13 = 12.5 v.
Pin 14 = 12.5v.

[dick_barton]

Re: Sharp LCD 32DH57E No power up.

Do you now have 60v dc at fuse F7700?

[Techstar]

Re: Sharp LCD 32DH57E No power up.

There is 56 . 2 Volts at both sides of the fuse , i have measured the voltage as far as JA102 this is a wire link on the same rail as the fuse. The fuse appeared to have a solder crack where it is soldered to the board , i have resoldered it but the set remains no go.

[budm]

Re: Sharp LCD 32DH57E No power up.

At this point the main board is not sending the PS-ON to turn on the power supply.

[Techstar]

Re: Sharp LCD 32DH57E No power up.

Not another main board problem :-(

[Techstar]

Re: Sharp LCD 32DH57E No power up.

I have decided to salvage all good parts off this tv and scrap it.
A good screen too , if anyone needs the screen message me.

[Techstar]

Re: Sharp LCD 32DH57E No power up.

Should the inverter board have switched on after forcing the power supply on, i am not too sure. ?

[Andrew F. Ali]

Re: Sharp LCD 32DH57E No power up.

Yes it should switch on upon forcing the PSU on. However, if there is no backlight load the PSU will shutdown and if the backlight have a shorted LED this too will shutdown the PSU.

[budm]

Re: Sharp LCD 32DH57E No power up.

Should the inverter board have switched on after forcing the power supply on, i am not too sure. ?

You need to force on BL-ON signal also to turn on the backlights circuit, it may also need DIm command too.

[Techstar]

Re: Sharp LCD 32DH57E No power up.

I have been looking at the connector pins on P7201 for the BL-ON pin , i can't make out which pin should be sent high to turn on the lights.
Could you advise what turn on voltage needs to be applied to which pin please .