Toshiba 48L3451DB dead 17IPS20 Rev6 psu

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Sorry, I mixed up two threads.
If the supplies come up when pin 1 & 2 of the opto U201 are lifted then I would check the voltages on Q205 and Q206.
Something is turning on the Opto-isolator when it should be off.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Theres 12v at R270/271 and 12v at R238 (briefly before they drop out) , nothing on R245 St_by.

Q205 E 0v, B 0.6v, C 0.06v

Q206 E 0v, B 0v, C 6v

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Can you connect a 1K resistor between ST_BY and +5V_STBY and then do the same test again

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Results are the same with a 1k res across st_by and +5v_stby on CN4.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

I've just been looking back through this thread. Earlier you said that you did not have the +5V_STBy. Is this still correct?

Q212 should have +12VCC on the collector and something like 6.8V on the base and 5V on the emitter. Can you check the voltages are there.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Oh yes, thats correct. NO +5v_stby, Q212 is not even there and the CN4 +5v_stby tracks do not go anywhere!

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Is there +5V_STBY at connector CN3 pin 9?

I cannot find a schematic that does not show Q212 as part of the circuit so all I can think of is if you could connect the 12V supply to ST_BY using the 1K resistor and see if that will bring up your supplies. Other than that I'm out of ideas.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

CN3 / 4 is the same connector.

Thanks, I appreciate your help!

[nomoresonys]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

You checked all the diodes, I would check any suspects out of circuit as suggested?

[budm]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Can I see good clear hi-res straight shots of the whole top and bottom side of the board? Your pictures in post #1 are cutoff.
BTW, the schematic is the master schematic for making blank PCB, so some of the parts may not be installed for your PCB Assembly.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Poor lighting at the moment but hopefully are good enough.

[budm]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

My post #30: "Can I see good clear hi-res straight shots of the whole top and bottom side of the board? Your pictures in post #1 are cutoff."

This in post #1 shows full top side of the board but too blur to read the part designators.
https://www.badcaps.net/forum/attach...2&d=1593464768

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

will have to do it tomorrow in proper lighting.

[budm]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

BTW, if you look at the schematic, you will see that the ST_BY (PS-ON) is active low not active high.
Bad part about Vestel board is that we need to find out what parts are installed and not installed to compared it to the schematic.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Hope these are better.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

The problem here is that with pins 1 & 2 opto-isolator (U201) lifted the the 12V and 24V supply come up (post #16).

This would indicate that the opto-isolator led must be off for this to happen and therefore Q205 must be switched off to achieve this. Taking ST_BY high switches on Q206 which removes the base drive voltage for Q205.

What's confusing is that this appears to contradict what others say.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Ok, just to confirm.
With U201 opto Pin 1 & 2 lifted out of circuit there is def a steady 12 & 24v rail.
This is with the main and backlight removed.

With just the backlight connected the 12 & 24v rails remain, no backlight.

With just the main connected the 12 & 24v rails drop in and out again.

[budm]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

The problem here is that with pins 1 & 2 opto-isolator (U201) lifted the the 12V and 24V supply come up (post #16).

This would indicate that the opto-isolator led must be off for this to happen and therefore Q205 must be switched off to achieve this. Taking ST_BY high switches on Q206 which removes the base drive voltage for Q205.

What's confusing is that this appears to contradict what others say.

I cannot see how that PNP Q216 is turned on if U201 LED side is lifted since the Base current for Q216 needs to flow through R258 (1K), Q207, and U201 (pin 4 -3) to ground.
If the VCC output is too high then the Zener diode D200 will conduct and turns on Q208 which will turn off Q207 in which turns off Q216 and repeat in cycle as long as ST_BY is low.
I wonder if the schematic matched your board.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Hi Budm, The schematic may be very similar to his board layout but it has already been noticed that there is no Q212 or +5V_STBY on that board.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Is there a link unsoldered or missing (Red circle) ???

Could you post a photo of the circuit within the yellow box in focus.