Toshiba 48L3451DB dead 17IPS20 Rev6 psu

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Replaced the Fan7529 ic but still just getting the 5v, 12v and 24v ramping up then dropping out.
Reading across the main cap C110 just sits at 335/6v.

It's C105 you need to check the PFC voltage across.

Can you post a picture of the solder side area around the Fan7529

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

In that case C105 reads 340v, jumps to 380v then drops.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Again it's attempting to but failing to start. Can you check the solder joint on pin 8.

I would double check all the solder joints in that area since you did get it up and running the first time you changed the IC so I'm suspecting a poor joint.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Re-flowed pretty much the whole board and still no joy.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

I don't know where to go next except to ask if you lift pins 1 & 2 of the opto as you did in an earlier post do all the supplies come up to their nominal values?

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Yep, get the 12v & 24v rails back up by lifting opto U201 pins1&2.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Can you post a photo of the area around U201 topside and bottom

Edit,
I remember you already have posted a photo of the underside but it's a little difficult to follow the tracks so if you can get a sharper image would be good.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Hopefully these are better.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Can you focus more on the area in the red box.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Sure.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

With pins 1 & 2 still lifted can you give the voltages on
Q207, Q208 and Q216 and also confirm you still have steady 12 & 24V

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

With pins 1 & 2 still lifted can you give the voltages on
Q207, Q208 and Q216 and also confirm you still have steady 12 & 24V

Q216
C - 0v
B - 15v fluctuating
E - 15v fluctuating

Q207
B - 15v fluctuating
E - 15v fluctuating
C - 15v fluctuating

Q208
B - 0v
E - 0v
C - 15v fluctuating

CN4 has 12v and 24v steady.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

The readings are what would be expected when not in standby but obviously not fluctuating.
What is interesting is that with Q216 is switched off (VCC = 0V so in standby mode) but you have the 12V and 24V supply.
But VCC operates RL100, U101 (PFC) and U300 (+12V/+24V)
Is the PFC voltage across C105 steady or is that fluctuating too.

With pins 1 & 2 soldered back in place can you repeat the readings. The readings must provide a clue to what is wrong.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Is the PFC voltage across C105 steady or is that fluctuating too.

C105 reads steady at 343v.

[notallbad]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

U201 pins 1 & 2 soldered back in.
Q216
C - sits at around 9.5v, rises to around 10v then drops to 8 7 and 6v then peaks up to 10v sometimes 12v then drops back down to 9.5v
B - sits at around 9.0v and rises to around 14-15v before dropping back down
E - sits at around 9.5v and rises to around 16v before dropping back down

Q207
B - sits at around 0.9v and gradually rises to around 10v before dropping back down to 0.9v
E - sits at around 0.2v and graduallt rises to around 9v before dropping back down to 0.2v
C - sits at around 0.2v and gradually rises up to around 10v

Q208
B - changes between 0.00v and 0.01v
E - changes between 0.00v and 0.01v
C - sits at around 0.9v and gradually rises up to around 10-12v before dropping back down

CN4 has 12v and 24v switching on and off again.

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

If I’ve read the circuit diagram correctly and there’s no guarantee that I have, here are my current thoughts.

VCC_MAIN is jumping about and since it generates VCC then that supply is affected likewise.

U101, the PFC controller is attempting to boost the incoming DC voltage but because VCC is unstable the boost voltage is also unstable.

U202 drives TR200 which generates VCC_MAIN (via D214 and D215) and is fed back to U202 (VDD pin) in order to maintain the smooth running of U202

VCC supplies the voltage for the relay RL100 and is also the supply voltage for U101 & U300

I believe the problem centres around VCC_MAIN being unsteady and brings me back to U202


Once again, I would check the components around the U202 and the VCC_MAIN path, D214, D215 and any electrolytic capacitors on that line.

U101 generates the PFC boost voltage
U202 generates the 12v & 24V supplies and also VCC_MAIN which then generates VCC supply.
U300 generates the +24V-80V (presumably for the led circuit)

If anyone else would like to offer their opinion, I'm sure it would be appreciated.

[nomoresonys]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Head scratcher, get the shotgun out and replace all those COMPONENTS just mentioned and the caps, WHAT else could it be??

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

I have to admit at the moment I'm out of any other ideas.

[nomoresonys]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

These guys appear to have a repair service and will price match, looks like they would earn their money on this one: https://www.tvparts.co.uk/lcd-tv-spa...stel-48l3451db

[dick_barton]

Re: Toshiba 48L3451DB dead 17IPS20 Rev6 psu

Check that they are back at work and not still in lockdown.