17IPS20 No Led Voltage Solved With Video :)

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

Here are the requested photos. May come in two sends as some are not fully clear so have sent a few more to help

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

The rest

[budm]

Re: 17IPS20 No Led Voltage Solved With Video

How many wires do you have on your LED connector?
How many LEDs per strip?

[budm]

Re: 17IPS20 No Led Voltage Solved With Video

BTW, after looking at pictures of your board and the pictures of OP's board in post #2, your board is not the same version as OP so the OP provides does not match your board.
Never mind about the LED, I see that you report as 9 LED's per strip (post #35), 7 strips total = 63 LEDs..
I am looking at many schematic versions for the PCB 17IPS20 to see which one matched your PCBA version, it looks to be PCBA 23155091.

[budm]

Re: 17IPS20 No Led Voltage Solved With Video

Remove (or lift one leg off the board) D503 (LED power supply booster diode) located closed to the LED connector, then check the RESISTANCE in both directions, also check that Lytic cap next to it to make sure it is OK.
BTW, Did someone solder the LED connector pins?
Also after looking through your pictures your board is 17IPS20 R6, see schematic of 17IPS20 R6 attached. Notes: not all component values of your board will match your PCBA because the schematic is the Master schematic for making PCB.

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

Hi
Sorry - I realised late last night that the cable to the LED connector was off so impossible to tell no. of cables to LED array - it is two ( a red + and a black -) so its one of these sets where all LEDS act as one strip as far as 3394S is concerned. LEDs are indeed 63 in total and board is 23155091 (it shows that on the label on board photos). Will go off and do the checks asked and report back. Thanks again for the time you are putting into it - much appreciated.

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

This board will drive me to insanity I think!
I took D503 out of board and it tests as ok and not open or shorted. Took the C505 out and checked it. No bulging, no shorting and tested as 46uf (should be 47uf when new). Both D503 and C505 had already shown to have 156v across them in circuit. Re-installed both and connected board back up.
On re-testing voltages across the points tested earlier found LED+ now putting out 165v instead of 156v as previously. Then found the last LED strip in the array before the cable returns to connector measured 58v on the +connector (as previously) but now 68v on the neg connector at the end of the strip !!!!!!!!!!!!!! - and also 68v back at the LED- connector tab.
On restarting the power a further couple of times I found LED+ was now showing 196V and remaining at that. Disconnect the array completely and LED+ remains showing 196v output. So something has definitely changed but no idea what? I wonder if a defective or slow FQPF7N80C could be the cause - or is that unlikely to cause a change to the voltage as shown?. I did try re-positioning the LED strips around and even substituting some but the new voltage changes and voltage differences described above after the last strip connector remain so I don't think it is a LED strip. But also (obviously) the voltage jumping to over 190v failed to trigger LED startup.

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

Sorry forgot to answer your question about soldering marks at LED connector. Yes that was me as I attached wires direct to the connections to also rule out a faulty cable or connector.

[budm]

Re: 17IPS20 No Led Voltage Solved With Video

"I took D503 out of board and it tests as ok" Did you test it using Ohm mode in both directions as I requested? The reason I have you test it using Ohm because I am looking for leakage resistance.
At 190 ~ 196 is more than enough to light up the LED string.
So at this point? Do you consistently get 190 ~ 196V every time you turn on the TV without the LED connected in place? We need this Voltage to be consistent first.

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

Hi,
Fired it up this morning and the 196v was now back again to 167v instant blip startup and then 156v constant after that! (no idea how that could happen!)
Took D502 back out of board and tested in both directions with multimeter set to Ohms this gave infinity in one direction and 114 in the other on the 200k setting. On diode setting it gave 0.458 in one direction and infinity in the other.
Worked further on the pcb long strip that the individual LED strips connect onto (these are apparently known to be a source of poor contact as they also have a connector in the middle) to ensure good connections and this did remove the discrepancy between the last strip pos and neg voltage readings reported above so neg reading now lower than pos connector reading ( but still 48v at end).
Whilst doing some further multimeter checks on these various connections I inadvertently left the meter on resistance setting (and not voltage) and on placing the red lead on the LED strip pos connectors with the black lead still to earth on board the LEDs all lit up to the touched connector point ( ie earthing the LEDs fired them up!). Is this normal as the LED strips aren't normally earthed to the chassis or board??
This is my first foray into LED as opposed to LCD backlights so really feel at a loss with the various outcomes I have been getting.
48 volts arriving back at the LED- board connector still seems too much to me ( 63 LEDs at 3 volts or even 2.5 volts should result in 0 volts arriving back to my simplistic mind). If I disconnect the LED connector completely I get 156v at LED+ terminal on board and 11.5 volts at LED- terminal on board (where does the 11.5 volts come from? the mosfet drain?)
And if I examine the board itself and follow the schematic this 48 voltage arrives straight back via the LED- terminal to the Q511 mosfet (FDD6N25 ) drain terminal. Is this excessive voltage arriving back at that terminal the problem ( and by my inadvertent short to earth it removed the 48v at the drain on Q511 allowing LEDs to light) ?
Your thoughts on this and corrections on my thinking would be very gratefully received.

[budm]

Re: 17IPS20 No Led Voltage Solved With Video

The LED Cathode return pin goes to ground via PWM controlled MOSFET Q511 and current sensing resistor to maintain constant current through the LED string. The MOSFET is driven by the LED controller IC, You have to check the drive Voltage at the Gate of the MOSFET to see if it is being driven or not by the LED controller IC.

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

Have checked mosfet Q 511 voltage and its 11.8 volts on both the Gate and the Source and doesn't deviate from that whether in standby, switched on, with the LED connector in or out. When switched off at wall the 11.8v slowly drops to zero on both pins understandably. On standby with LED cable removed the Led-/Drain voltage is 11.8v. I have also checked the voltage on both source and gate pins on mosfet Q502 as suggested by ReecyB in his video and they both show 0v under the above scenarios with no deviation from that.
I wonder given all of these measurements now provided you are any nearer suggesting a possible cause or faulty component?
Regards
John

[budm]

Re: 17IPS20 No Led Voltage Solved With Video

Have checked mosfet Q 511 voltage and its 11.8 volts on both the Gate and the Source and doesn't deviate from that whether in standby, switched on, with the LED connector in or out. When switched off at wall the 11.8v slowly drops to zero on both pins understandably. On standby with LED cable removed the Led-/Drain voltage is 11.8v. I have also checked the voltage on both source and gate pins on mosfet Q502 as suggested by ReecyB in his video and they both show 0v under the above scenarios with no deviation from that.
I wonder given all of these measurements now provided you are any nearer suggesting a possible cause or faulty component?
Regards
John

For Q511 to be on, the Voltage on the Gate should be around 3V or more above the Source Voltage, that means LED Driver IC is not working so we need to find out why, the current return of the LED string goes through the IC U500 (MP3394), so you need to test Voltages at U500 but you should verify that the IC is MP3394 per schematic.

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

Thanks.
U500 on this set is MP3394S. What status do I test it in? ie On with LEDs connected or which?
I'm away for 4 days now so will post back after testing done (probably just after the weekend.
Regards

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

Is MP3394S the only critical number on the chip (especially if it needs replacing)?

[budm]

Re: 17IPS20 No Led Voltage Solved With Video

Thanks.
U500 on this set is MP3394S. What status do I test it in? ie On with LEDs connected or which?
I'm away for 4 days now so will post back after testing done (probably just after the weekend.
Regards

Just check and report the Voltage reading of each pin of the IC when you turn on the TV, look at the spec sheet of the IC then report the readings in this format:
Pin 1 COMP = xx V
Pin 2 EN = xx V
....
.....
.....

[budm]

Re: 17IPS20 No Led Voltage Solved With Video

Is MP3394S the only critical number on the chip (especially if it needs replacing)?

Look at page 2 of the spec sheet, you will see that there are 3 package types, so look at what you have on your board.

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

Hi - Back now so have taken the measurements you asked for on MP3394S.
Although the datasheet you provided was for MP3394 and not MP3394S the pin descriptions read the same and I assume the readings they should both give would be the same. The package type is SOIC16.
The readings are as below:
Pin 1 COMP 0.1v
Pin 2 EN 3.2v
Pin 3 DBRT 2.0v
Pin 4 GND 0.0v
Pin 5 OSC 0.3v
Pin 6 ISET 0.0v
Pin 7 BOSC 0.0v
Pin 8 LED4 12.9v
Pin 9 LED3 12.8v
Pin 10 LED2 12.8v
Pin 11 LED1 12.7v
Pin 12 OVP 0.6v
Pin 13 ISENSE 0.1v
Pin 14 GATE 0.1v
Pin 15 VIN 11.8v
Pin 16 VCC 0.1v

Does this help to pinpoint any faulty component?

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

Just a minor followup -
I decided to measure on each pin whilst taking the board from standby to on and all pins showed the voltages above except Pin 3 DBRT went to 3.2v before returning to 2.0v. Also Pin 2 EN took several seconds before showing its 3.2v reading.
Pins 8,9,10 and 11 ( The LED pins) stayed at 11.8v when in standby

[budm]

Re: 17IPS20 No Led Voltage Solved With Video

Hi - Back now so have taken the measurements you asked for on MP3394S.
Although the datasheet you provided was for MP3394 and not MP3394S the pin descriptions read the same and I assume the readings they should both give would be the same. The package type is SOIC16.
The readings are as below:
Pin 1 COMP 0.1v
Pin 2 EN 3.2v
Pin 3 DBRT 2.0v
Pin 4 GND 0.0v
Pin 5 OSC 0.3v
Pin 6 ISET 0.0v
Pin 7 BOSC 0.0v
Pin 8 LED4 12.9v
Pin 9 LED3 12.8v
Pin 10 LED2 12.8v
Pin 11 LED1 12.7v
Pin 12 OVP 0.6v
Pin 13 ISENSE 0.1v
Pin 14 GATE 0.1v
Pin 15 VIN 11.8v
Pin 16 VCC 0.1v Bad

Does this help to pinpoint any faulty component?

Pin 16 VCC pin should be 6V per spec sheet, it is an internal 6V LDO regulator.
So no power to the TV then check the resistance between VCC pin and Ground to see how many Ohms it shows.