Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

[triplefour]

I picked up a tv yesterday and the woman who gave it to me said it had sound but no picture. When I picked it up I noticed the lcd was cracked so I aeked her if that was the original problem or if it got cracked after but she really didn't know. So I get the tv home thinking hey if it's just a cracked screen then I scored some good parts maybe to sell on ebay or use to fix someone's tv locally. But of course it's not always so simple...
The tv does not turn on. Light goes green for 30 seconds while it tries. Flickers once and stays green again for a little while longer and then goes solid red for a couple seconds, followed by 5 red flashes, a pause and then 6 red flashes to infinity. Checking voltages on the psu I see the 12v come up when it's in green light trying to turn on mode, and then I even see 3v on BL-ON for a second before that goes back to 0.
So I check the backlights with the tester which shows me that 3 out of the 4 strings are fine and draw about 90v when lit up but one of them is open circuit.

I would like to make some kind of dummy load out of resistors that would trick the psu to think that everything was fine with that string so the tv could continue booting up and I could verify picture and sound function. I just don't know enough to figure out what resistor value I should put there or if that's even a thing that's safe to do. Thought I saw it somewhere on here but I'm not sure. Someone set me straight please!

[triplefour]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

Also this problem comes up pretty often. It would be nice if I could buy or make some kind of device that could set a range of different loads. Is there such a thing? A universal load generator?

[chrismurphy]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

try a 90 volt zener with a pass transistor may work

https://electronics.stackexchange.co...nt-for-a-zener

[budm]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

I picked up a tv yesterday and the woman who gave it to me said it had sound but no picture. When I picked it up I noticed the lcd was cracked so I aeked her if that was the original problem or if it got cracked after but she really didn't know. So I get the tv home thinking hey if it's just a cracked screen then I scored some good parts maybe to sell on ebay or use to fix someone's tv locally. But of course it's not always so simple...
The tv does not turn on. Light goes green for 30 seconds while it tries. Flickers once and stays green again for a little while longer and then goes solid red for a couple seconds, followed by 5 red flashes, a pause and then 6 red flashes to infinity. Checking voltages on the psu I see the 12v come up when it's in green light trying to turn on mode, and then I even see 3v on BL-ON for a second before that goes back to 0.
So I check the backlights with the tester which shows me that 3 out of the 4 strings are fine and draw about 90v when lit up but one of them is open circuit.

I would like to make some kind of dummy load out of resistors that would trick the psu to think that everything was fine with that string so the tv could continue booting up and I could verify picture and sound function. I just don't know enough to figure out what resistor value I should put there or if that's even a thing that's safe to do. Thought I saw it somewhere on here but I'm not sure. Someone set me straight please!

For this one you can try 1K 10W in place of the open LED string, you can also put 1W white LED in series as indicator.

[petehall347]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

back in the olden days when screens used them very thin tube lights i used to have some spare ones for such testing purposes .
i guess its easy enough to build a nice test set of led,s .

[budm]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

BTW, what is the P/N of the LED driver IC701?
https://www.shopjimmy.com/sony/kdl-60ex645
Is your power supply board the same as shown at Shopjimmy?
If it is, then you should try with 2K 5W (it will get hot) first for quick test.

[triplefour]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

I think I do have the same board as on shopjimmy.
880101100-065-G
The markings on ic701 are
2AA9F5T
DDA009

I would like to understand how to calculate the appropriate resistor to use for future tvs. Can you elaborate or point me in the direction where that has already been covered? Thank you

[budm]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

Base on 90V reading on your LED tester, if the LED are 3V each and your LED tester is only putting out about 30mA so the Vf of white LED at 30mA will be about 2.7 ~ 2.8V, 90V/2.8V = 32 LEDs, so if they drive LED at 100mA or so, the Vf of each LED will be about 3V, so 3V x 32 = 96V for LED string.
So if we are try for 50mA at 96V, the resistor will be about 2K Ohms, at 100mA will be about 1K Ohms, these are just estimation, the Wattage rating of the resistor should be twice the power dissipation.
So try with 2K to see if the backlights circuit will stay on or not.

[triplefour]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

OK I will look around and see if I have those resistors laying around in the scrap pile somewhere. I see now how you calculated it with ohms law but how can we be sure the leds are the 3v kind? I've seen some that were different. Also how can I be sure what amps my led tester is outputting? It doesn't say on the case anything about the output...

[budm]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

The calculation is based on what your LED tester shows, the Total Vf of the LED string,
If they are 6V LED, then the Vf at 30mA will be about 5.6V, so that will be 16 LEDs in the LED string instead of 32 LEDs.
You probably do not have the newer LED tester that can do 200mA or more which is good for real drive current test, older one only drives about 30mA, 50mA most. You can find out by hooking up the 100 Ohms resistor to it and see what what the Voltage reading is then you can calculate the drive current.
See graph in the LED spec sheet for Vf graph.

[budm]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

BTW, you also need to realize that when you use the LED tester, the LED strip will still light up with some shorted out LED so you cannot tell for sure what the VF of the LED string really is if it has some shorted LED's.
In your case you have 4 LED strings and 3 of them show the same Vf readings so you can basically tell what the Vf should be for all 4 strings.
Some TV may have two LED strings with its own LED driver for each string, but the two strings do not have the same amount of LED's.
Basically, you should try to find out how many LED's there are in the LED string.

[triplefour]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

Thank you for clarifying. What you say makes sense. I will get back when I find those resistors

[yokoono]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

Backlight tester
https://www.youtube.com/watch?v=FtTcC0hJ7Q4
https://www.youtube.com/watch?v=4DS8_utsLPo

[triplefour]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

If I am looking to salvage these parts from scrap boards, how can I know the wattage of a resistor if it doesn't say on the resistor itself? Most of them that ive seen dont. Same question for the 1w white led. What would be the test I would do to determine the wattage of a resistor or led?

[budm]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

Just go to MOUSER or DIGIKEY and look up spec sheet of the resistor and get the dimension for the Wattage of the type of resistor (I.E Through hole MOX, METAL FILM, CARBON FILM).
https://www.digikey.com/products/en/...MOX%20RESISTOR
For LED you will need to look at the spec sheet.

[triplefour]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

I couldn't find any in my scrap pile so I went ahead and ordered some from ebay. I paid about 10$ total for 2 of the 2k5w and 1 1k10w. Paid more cause I don't want to wait for it to come from china. So I'll be back to report what happens when those come in. Budm, do you have a led tester you would recommend? The ones I see on ebay look cheap like mine and don't list the output current.

[vinceroger69]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

https://www.ebay.co.uk/itm/0-320V-Ou...sAAOSwmTddMocD
i was thinking of buying this

[budm]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

This one is supposedly can drive up to 300mA but I do not know how true that is since it can be Chinese spec.; I am sure you can get it cheaper from EBAY.
Mine only does 30mA, I bought it a long long time ago.
https://www.amazon.com/IFIX-RT300M-N.../dp/B078X4V4JQ

[triplefour]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

Vinceroger69 that meter is about the same price as the one I got but it's cooler in that it displays the amps as well as volts but still it only outputs 35ma max.
Budm that one is also very cheap but says it does 300ma...intriguing. Would be worth buying just to find out if it's real. I might do that.

[nomoresonys]

Re: Sony Kdl-60ex645 bad LED how to use dummy load to trick it?

https://www.aliexpress.com/item/3285...5c24401b25ceO9