42inch Touch Screen wont power on

[tom66]

Re: 42inch Touch Screen wont power on

Before you look for Vcc/start up problems, check the output diodes for shorts. I was chasing around a problem like that on a DVD player (Vcc measured very low, about 1-2V) and it turned out the shorted diode on the secondary was not allowing the supply to bootstrap and supply the "run" power. If Vcc is still giving issues and diodes are not shorted, check the zener (if present), resistor and cap... Good luck.

[epicfatigue]

Re: 42inch Touch Screen wont power on

Voltage moved upwards and keeptclimbing i took it of at 85mv

it has massive resitance btw

[epicfatigue]

Re: 42inch Touch Screen wont power on

C= 330v
D= 120mv

and fuck me i touched the powerinvertor with my hand lmfao that shit hurts.

i shall check #25 shortly as i have to feed my dauhter

[retiredcaps]

Re: 42inch Touch Screen wont power on

Hey so the 4.7uf 50V cap located on Diagram as A recorded 23.7mv

If A is indeed the startup cap, that voltage is way too low.

Regon B all the caps recorded 0 V

As expected because the SMPS hasn't started.

Should i measure C and D voltage?

Whats my next step i feel as if i am making progress.

C will be 165 V DC. We know it works because we get 5 V standby. D might be the startup cap for the 5 V SMPS, but I'm not sure. It wouldn't hurt to measure it.

Also, waiting for post #25 tests 1 and 4.

[epicfatigue]

Re: 42inch Touch Screen wont power on

Hey so the 4.7uf 50V cap located on Diagram as A recorded 23.7mv

Regon B all the caps recorded 0 V

Should i measure C and D voltage?

Whats my next step i feel as if i am making progress.

[retiredcaps]

Re: 42inch Touch Screen wont power on

If you are measuring capacitance of the electrolytic caps, then black probe goes to negative (usually stripe on the sleeve) and red probe goes to positive.

If you are measuring DC voltage of electrolytic caps, it is the same. Namely, black probe goes to negative (usually stripe on the sleeve) and red probe goes to positive.

[epicfatigue]

Re: 42inch Touch Screen wont power on

Generally, yes, but see datasheet to confirm pin numbering and orientation.



You can measure the uF if you want, but you have to desolder them to get an accurate reading. Plus I know of no multimeter that can measure ESR which is more important.

You want to see DC voltage from the startup cap.



For the mosfets, I normally test for shorts. I measure pin 1-2, 1-3, and 2-3. Any reading under 30 Ohms "in circuit" suggests a possible short.

Awesome well i will measure the mosfets for shorts and check the DC voltage for the caps, gunna be fun powering up this baby and checking the voltages.

I have one question on polarized, variable and standard caps.

Stop me if i am wrong.

Polarized i just have to follow neg with positive -) |-+ (ie positibe on right neg on left ?

variable and standards i can do it either way ? or do i have to use a common ground and touch the opposite side of it.

[retiredcaps]

Re: 42inch Touch Screen wont power on

Okay Shall do, does the Dot represent PIN 1?

Generally, yes, but see datasheet to confirm pin numbering and orientation.

Should i measure the capacitance of all the caps? or even the startup cap while we wait to confirm the part number? also what kind of voltage should i see comming off these caps?

You can measure the uF if you want, but you have to desolder them to get an accurate reading. Plus I know of no multimeter that can measure ESR which is more important.

You want to see DC voltage from the startup cap.

And also can i measure the Powermosphets while in circuit?
And if so what is the correct way to test them? from memory they were a gate of some kind.

For the mosfets, I normally test for shorts. I measure pin 1-2, 1-3, and 2-3. Any reading under 30 Ohms "in circuit" suggests a possible short.

[epicfatigue]

Re: 42inch Touch Screen wont power on

Okay Shall do, does the Dot represent PIN 1?

Should i measure the capacitance of all the caps? or even the startup cap while we wait to confirm the part number? also what kind of voltage should i see comming off these caps?

And also can i measure the Powermosphets while in circuit?
And if so what is the correct way to test them? from memory they were a gate of some kind.

Furthermore i removed the Panel from the touchscreen unit and it is a LG panel, should i record the number for use on here? or is there no need as LG panels are used in lots of tvs.

[retiredcaps]

Re: 42inch Touch Screen wont power on

Chip looks like

L 6 5 9

May have spoke too soon about not finding the part number. Digikey has this "L6599A"

https://cdn.badcaps-static.com/pdfs/...d758189067.pdf

I'll need someone with more experience to confirm, but if it is correct part, then we are interested in measuring pin 12.

Pin 12 is the vcc. It needs between 10 and 11.4 V DC to turn on. From page 32, it looks like that should come from a 10uF capacitor. That 10uF capacitor could be the one just below the big SMPS and just to the right of the Powerview logo?

Tests
===

1) See if pin 12 (vcc) is shorted to pin 10 (gnd). Any resistance reading less than 30 ohms suggests it is bad. If yes, I believe that indicates L659 is bad.

2) Since you will have to do board acrobatics to get readings, find a piece of cardboard to rest the board on so you don't accidentally short out anything.

3) Carefully measure the DC voltage across the 10uF startup cap. Note the voltage and if it is steady of fluctuating. Black probe on negative leg and red probe on positive leg of cap.

4) Measure the DC voltage on pin 12. Be CAREFUL not to let the probe slip and short out the IC. Again, note the voltage and if it is steady of fluctuating. Use pin 10 for ground.

[retiredcaps]

Re: 42inch Touch Screen wont power on

I thought they were Power mosphets?

They could be combination power mosfet and smps. I can't recall which monitor, but there was one case where the two functions were integrated into one chip.

[epicfatigue]

Re: 42inch Touch Screen wont power on

I thought they were Power mosphets?

I am at work at the moment i can check when i come home be home in 2 hours.

I did notice on the far left hand side one of those atached to the heatsink is showing some discoloration and no others are.

[retiredcaps]

Re: 42inch Touch Screen wont power on

Hmm, no luck with either part number.

What about those 2 ICs on the heatsink just above the Powerview logo? What are the part numbers of those two?

[epicfatigue]

Re: 42inch Touch Screen wont power on

Chip looks like

L 6 5 9 (and 2x symbols that look like a light bulb and a capital D)
(84 inside a circle) 9 0 7 B 6 5 0

[epicfatigue]

Re: 42inch Touch Screen wont power on

Hey yes there is another chip on the back, has 16 legs and is located near the cold side of the board.

Ill just get the Camera out and take a close up of it only way i can read the markings.

[retiredcaps]

Re: 42inch Touch Screen wont power on

1) It is Fan6527b which is a PFC controller.

2) Please post a picture of the entire backside as well.

3) Anymore chips on the back?

4) If there are no more chips on the backside, the SMPS could be integrated with the power mosfet. This would be one of the transistors mounted on a heatsink on the front side.

[epicfatigue]

Re: 42inch Touch Screen wont power on

looks like FPG68H (8 could be B) FAN75278 (8 could be B)

[retiredcaps]

Re: 42inch Touch Screen wont power on

CN06 (C on my diagram)
Pin 1 Legand Says 24V - My reading 0
Pin 2 Legand Says 24V - My reading 0
Pin 3 Legand Says 24V - My reading 0
Pin 4 Legand Says 24V - My reading 0
Pin 5 Legand Says 24V - My reading 0

CN06 (all the colors) looks like it powers the inverter board. No power means no backlight.

CN04 (D on my diagram)
Pin 1 LEgand Power - My reading - 2.947V
Pin 4 LEgand 5V - My reading - 157.9mV
Pin 5 LEgand 5V - My reading - 157.9mV
Pin 6 LEgand 5Vs - My reading - 5.23V

5Vs is your standby which is working.

Pin 1 = power could be working. Some TVs use 0 V and some use > 2 V to signal power on. Let's assume it is working.

So now the problem is that the SMPS is not starting since we are missing 5, 12, and 24 V DC.

We will need a picture of the backside of the power board. We are looking for a 8 legged IC (or more) that is the smps chip. We need the part number and its datasheet.

This chip could be bad or the startup cap (usually a little one in the range of 22uF to 50uF) is bad.

PS1. There is a small white SMD fuse on the inverter board just next to the yellow colored cap.
PS2. What type of multimeter (I'm curious).

[epicfatigue]

Re: 42inch Touch Screen wont power on

Main Fuse checks = .1 ohms

Bridge rectifier
1-2 = .916 M
1-3 = 3.62 M
1-4 = 1.13 M
2-3 = 381.1 k
2-4 = 4.50 M
3-4 = 4.50 M

CN06 (C on my diagram)

Pin 1 Legand Says 24V - My reading 0
Pin 2 Legand Says 24V - My reading 0
Pin 3 Legand Says 24V - My reading 0
Pin 4 Legand Says 24V - My reading 0
Pin 5 Legand Says 24V - My reading 0
Pin 6 Ground
Pin 7 Ground
Pin 8 Ground
Pin 9 Ground
Pin 10 Ground
Pin 11 Blank
Pin 12 Blank
Pin 13 my reading 0
Pin 14 My Reading 0

CN04 (D on my diagram)
Pin 1 LEgand Power - My reading - 2.947V
Pin 2 LEgand GND - My reading - 0
Pin 3 LEgand GND - My reading - 0
Pin 4 LEgand 5V - My reading - 157.9mV
Pin 5 LEgand 5V - My reading - 157.9mV
Pin 6 LEgand 5Vs - My reading - 5.23V
Pin 7 LEgand GND - My reading - 0
Pin 8 LEgand GND - My reading - 0
Pin 9 LEgand 12v_C - My reading - 49.4mV
Pin 10 LEgand 12v_C - My reading - 49mV
Pin 11 LEgand INV_d1 - My reading - 0
Pin 12 LEgand unknown - My reading - 0
Pin 12 LEgand unknown

When i measured this i ensured all lead are unpluged except the voltage comming from power socket.

When all leads are plugged in a relay clicks in power supply and nothing happens.

I looked high and low for another fuse marked F and could not see one.

What is my next step something is clearly wrong here

[retiredcaps]

Re: 42inch Touch Screen wont power on

If the rectifier is shorted, then there is no need to do all the DC voltage measurements on the hot and cold side.