Backlights but no picture - No 12v to Tcon board

**nomoresonys** · 10-23-2019, 04:41 AM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by Stuckster

Tcon fuse is good. I believe the 12v is sent to the Tcon via the 51pin LVDS cable. So I would presume that there will still be no 12v with the LVDS unplugged, but I will test it anyway.

LOL, I meant is there voltage at the spot on mainboard where you expect it without the lvds cable hooked up.

**dick_barton** · 10-23-2019, 04:49 AM

Re: Backlights but no picture - No 12v to Tcon board

Sorry, my mistake. Posted the wrong picture. Can you give the numbers on the two IC's in the red boxes. The yellow boxes have voltage regulators. Can you measure the voltage on the 3 pins of each.

Attached Files

**Stuckster** · 10-23-2019, 05:00 AM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by dick_barton

Sorry, my mistake. Posted the wrong picture. Can you give the numbers on the two IC's in the red boxes.

No problem. It's tricky to read but I think they are
Top IC
P3056LS
15 10

Middle IC
4832
GA5614

Bottom IC
4832
GA5614

**Stuckster** · 10-23-2019, 05:06 AM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by dick_barton

The yellow boxes have voltage regulators. Can you measure the voltage on the 3 pins of each.

Top VR
Top pin = 0.0v
Middle pin = 3.3v
Bottom pin = 5.1v

Bottom VR
Top pin = 5.1v
Middle pin = 3.3v
Bottom pin = 0.0v

Thanks

**dick_barton** · 10-23-2019, 05:10 AM

Re: Backlights but no picture - No 12v to Tcon board

Can you give the voltages on the IC pins. I suspect one of them may have the 12V but is not switching through to the Tcon.

Attached Files

**dick_barton** · 10-23-2019, 05:30 AM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by Stuckster

Top VR
Top pin = 0.0v
Middle pin = 3.3v
Bottom pin = 5.1v

Bottom VR
Top pin = 5.1v
Middle pin = 3.3v
Bottom pin = 0.0v

Thanks

They look fine and provides the 3V3 supply to other IC's

**Stuckster** · 10-23-2019, 05:36 AM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by dick_barton

Can you give the voltages on the IC pins. I suspect one of them may have the 12V but is not switching through to the Tcon.

Top IC
11.9 --- 0.0
11.9 --- 0.0
11.9 --- 0.0
11.5 --- 0.0

Middle IC
1.1 --- 3.5
1.1 --- 0.0
23.6 --- 3.2
23.6 --- 1.4

Bottom IC
9.9 --- 2.3
9.9 --- 0.0
23.6 --- 12.7
23.6 --- 9.9

Top one looks like it might be the culprit? It's also the closest to the LVDS cable connection point.

**Stuckster** · 10-23-2019, 05:38 AM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by nomoresonys

LOL, I meant is there voltage at the spot on mainboard where you expect it without the lvds cable hooked up.

No voltage on the LVDS connector pins (with cable unplugged).

**dick_barton** · 10-23-2019, 05:41 AM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by Stuckster

Top IC
11.9 --- 0.0
11.9 --- 0.0
11.9 --- 0.0
11.5 --- 0.0

Middle IC
1.1 --- 3.5
1.1 --- 0.0
23.6 --- 3.2
23.6 --- 1.4

Bottom IC
9.9 --- 2.3
9.9 --- 0.0
23.6 --- 12.7
23.6 --- 9.9

Top one looks like it might be the culprit? It's also the closest to the LVDS cable connection point.

Can you give the IC name and pin numbers 1 to 8 as shown in the images which makes reading easier.

**Stuckster** · 10-23-2019, 05:58 AM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by dick_barton

Can you give the IC name and pin numbers 1 to 8 as shown in the images which makes reading easier.

Sure.

SOP-8L (top)
1. S - 11.9
2. S - 11.9
3. S - 11.9
4. G - 11.9
5. D - 0.0
6. D - 0.0
7. D - 0.0
8. D - 0.0

SOIC-8 (middle)
1. S2 - 1.4
2. G2 - 3.2
3. S1 - 0.0
4. G1 - 3.5
5. D1 - 1.1
6. D1 - 1.1
7. D2 - 23.7
8. D2 - 23.6

SOIC-8 (bottom)
1. S2 - 9.9
2. G2 - 12.7
3. S1 - 0.0
4. G1 - 2.3
5. D1 - 9.9
6. D1 - 9.9
7. D2 - 23.7
8. D2 - 23.7

Hope I've got them right.

**dick_barton** · 10-23-2019, 06:28 AM

Re: Backlights but no picture - No 12v to Tcon board

I believe the gate voltage should be at least 1.5V lower than the Source voltage so it looks as though the IC is not being switched on to allow the 12V through to the Drain which is probably the 12V supply for the tcon. You can check this out. With the set switched off check the resistance between the fuse on the Tcon and the Drain of the P3056LS
Could you also check the resistance between the Gate and Sourse and Gate and Drain.

**Stuckster** · 10-23-2019, 06:32 AM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by dick_barton

I believe the gate voltage should be at least 1.5V lower than the Source voltage so it looks as though the IC is not being switched on to allow the 12V through to the Drain which is probably the 12V supply for the tcon. You can check this out. With the set switched off check the resistance between the fuse on the Tcon and the Drain of the P3056LS
Could you also check the resistance between the Gate and Sourse and Gate and Drain.

Just realised I made a small typo. Gate should be 11.5 (not 11.9)
P3056LS
1. S - 11.9
2. S - 11.9
3. S - 11.9
4. G - 11.5
5. D - 0.0
6. D - 0.0
7. D - 0.0
8. D - 0.0

**Stuckster** · 10-23-2019, 06:57 AM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by dick_barton

With the set switched off check the resistance between the fuse on the Tcon and the Drain of the P3056LS
Could you also check the resistance between the Gate and Source and Gate and Drain.

Ok. Resistance between Tcon fuse and drain on P3056LS is .001 (just the resistance of my leads). So no resistance.

Resistance between Gate and Source is 33 (meter set to 200k Ohms)
Resistance between Gate and Drain is 90 (meter set to 200k Ohms)

I'm only a novice when it comes to this stuff. So thanks for your patience.

**dick_barton** · 10-23-2019, 08:48 AM

Re: Backlights but no picture - No 12v to Tcon board

The resistance from the Tcon fuse to Drain being 0.001 means that P3056LS should be providing the 12V Tcon supply.
The other resistance readings, 200K ohms means there is no internal short circuit from gate to the source

The problem is that the IC is not being switched on.

Can you take a really sharp photo around that IC to try and see what the Gate track is connected to.

**Stuckster** · 10-23-2019, 05:46 PM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by dick_barton

The resistance from the Tcon fuse to Drain being 0.001 means that P3056LS should be providing the 12V Tcon supply.
The other resistance readings, 200K ohms means there is no internal short circuit from gate to the source

The problem is that the IC is not being switched on.

Can you take a really sharp photo around that IC to try and see what the Gate track is connected to.

Sure. Try this.
Now the first thing you're going to say is, that's a different IC! Which is true.

I should explain that I currently have two mainboards (same model). Lets call them A and B. Board A is the original board that came with the set. It failed and has too much wrong with it to resurrect. Board B is a replacement board that I bought "in used working condition". It is the board that I have been talking about in this thread. All the voltage and resistance readings have come from board B.

When you asked for the IC numbers I assumed (wrongly) that the parts on each board would be identical. It was easier to give you the part numbers from board A since I had it on the desk and could easily take the heat sink off etc. Apologies. Nevertheless having looked up the specs for the PMK50XP IC on board B (the one in the close up photo) they appear to have the same specs and function.

Attached Files

**budm** · 10-23-2019, 06:13 PM

Re: Backlights but no picture - No 12v to Tcon board

https://www.badcaps.net/forum/attach...2&d=1571874353
SOP-8L (top)
1. S - 11.9
2. S - 11.9
3. S - 11.9
4. G - 11.9
5. D - 0.0
6. D - 0.0
7. D - 0.0
8. D - 0.0

So if you check the resistance between the T-CON fuse and D pin of Q1, it shows about the same resistance of the meter's probes resistance?

**Stuckster** · 10-23-2019, 06:46 PM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by budm

https://www.badcaps.net/forum/attach...2&d=1571874353
So if you check the resistance between the T-CON fuse and D pin of Q1, it shows about the same resistance of the meter's probes resistance?

Yes. Correct. I just measured it again.
With the meter set on 2k Ohms it 's reading 0.001 Ohms to all D pins.
With the meter set on 200 Ohms it 's reading 1.5 Ohms to all D pins.

**budm** · 10-23-2019, 09:06 PM

Re: Backlights but no picture - No 12v to Tcon board

https://www.badcaps.net/forum/attach...2&d=1571874353
Put DC Volt meter black lead on the chassis, Red lead to the Base pin of Q2 then turn the TV ON and OFF (wait 5 seconds between toggling) to see if the Voltage on the Base pin of Q2 changed state when you toggle the TV ON and OFF.

**Stuckster** · 10-24-2019, 01:02 AM

Re: Backlights but no picture - No 12v to Tcon board

Originally posted by budm

https://www.badcaps.net/forum/attach...2&d=1571874353
Put DC Volt meter black lead on the chassis, Red lead to the Base pin of Q2 then turn the TV ON and OFF (wait 5 seconds between toggling) to see if the Voltage on the Base pin of Q2 changed state when you toggle the TV ON and OFF.

Sure. Is the base pin the one on it's own? Sorry I'm a bit of a noob with pcbs.

**budm** · 10-24-2019, 01:11 AM

Re: Backlights but no picture - No 12v to Tcon board

https://www.badcaps.net/forum/attach...2&d=1571874353

Emitter pin (Top) is connected to R125/C181
Collector pin (Middle pin) is connected to R126
Base is the bottom pin.

Backlights but no picture - No 12v to Tcon board

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