Toshiba 48L3451DB dead 17IPS20 Rev6 psu

[notallbad]

No front stby light.

With backlight and main bd disconnected only getting fluctuating voltages that drop out almost straight away on CN4, none appear to ramp up to the correct voltage, drop out almost straight away. It seems to be a 6 second constant restart loop.

U300 & U202 Fan6300A
U101 FAN7529

Not sure these are related to my problem but thought I would mention them.

340v across C110 goes up and down a little.
Not getting the constant 12v or 24v.

Checked all the 0 ohm resistors, all ok.
Checked diodes, seem ok but a couple need double checking as reading same both ways.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

What voltage do you have across the legs of C105?
Do you have the +5V_STBY ?

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

What voltage do you have at Pin 6 (VCC) of U202 (FAN6300) when you power up.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

What voltage do you have at Pin 6 (VCC) of U202 (FAN6300) when you power up.

That jumps around between 8 - 16v, using C110 leg as gnd.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

What voltage do you have across the legs of C105?
Do you have the +5V_STBY ?

Theres no 5v on CN4 PIN 9 (Can't find a C105 on the board), don't think its populated on this board, traces back to Q212 which is not there.

Pin 1 get 24v thats drops out
Pins 10,11 & 12 get 12v that drops out

Using chassis as gnd.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

C105 is one of the two large capacitors side by side.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

That jumps around between 8 - 16v, using C110 leg as gnd.

Without looking up the datasheet for the FAN6300A I would think that the 16V would be enought to kickstart it into operation.

I would check D928, D213, Q215, Q211, D510 & D511

Edit
Datasheet says turn on voltage for the FAN6300A is 16V so it looks like the circuit is constantly trying to turn on.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

I suspect that those components are OK. The FAN6300A must be kickstarting in order that initially the 12V and 24V come up.
However the secondary supplies are not being maintained so I wonder if it's a feedback problem with one of the opto's possibly U200/U201 not turning on?

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

I can't see the lettering on the power supply. Is there a CN3 and is the 24V coming up on pin 1

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

I see from an earlier post that you do get the 24V which drops.
Have you lifted the diodes (at least one leg) that you referred to earlier and checked them out of circuit.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

The smd diodes I referred to earlier giving same reading both ways I suspect are ok, they read the same both ways as they are in parallel to low ohm resistors i e one to a 220ohm and another to a 10 ohm resistor.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

How about the large diodes on the top of the pcb. i.e D209, D210, D211 etc

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

SB5B5's read 220 ooc.

UF5404 reads 290 ooc.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

U300 - FAN6300 pin 6 only gets 12v, mostly only 10v.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

U200 - PC817 gets 12v at pin 1 which drops out
U301 - PC817 gets 16v at pin 1 which drops out
U201 - PC817 only reads 1.15v and not really budging

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Pull pin 1 and 2 on U201 - PC817 and the volts 24v and 12v remain constant on CN4.
Steady 12v on pin 1 with Pc817 out, replace with an EL817 and voltage same as before.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

I don't quite understand what you mean.
Pull pin 1 & 2. Do you mean lifted the pins out of circuit.
Replace with EL817 and voltage same as before. Do you mean it comes up and then drops.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Yh. sorry.
Lift pins 1 & 2.out of circuit and 12v and 24v rails on cn4 are good.

Replaced PC817 with an EL817 (all I have in my spares.bucket) and the 12v and 24v start going up and down again.
The voltage on pin 1 of PC817/EL817 is 1.15v with it back in.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

I've been searching the forum for this power supply and I think that this is an "always on" power supply so with U201 replaced it may well now be working. Remove the 1K jumper resistor and check for 12 & 24V supplies.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Replaced U201 and tried back in tv but still nothing.

Can't find the 1k res, the board is different to the sch provided above. Some differences as I'm sure your aware with these boards and schemas.