Hello everyone, I got a TCL 75S421 with no backlight. I swapped out the LEDs and still getting nothing. I checked a few readings, see pictures below. Can anyone point me in the next testing area or what to look at next?
Attached Files
-
-
Hello, you will want to check a capacitor. I have replaced many of them in this power supply. When you remove it you will feel a slight bulge on one of the sides. It is c614a . Hope this helps. -
I recommend removing c614a and feel it between your fingers. It’s usually very slightly bulged on one of the sides. Normally you cannot see it until after you have felt it. If you have an exact match for that capacitor definitely just replace it and see if that resolved your issue. Also one thing about this board it is very easy to short out the transistors when testing them. If you have tested them and got any kind of zap from your meter leads, that it’s likely something has shorted.Comment
-
Did you test the new leds with led tester from the connection that plugs into PSU? I have, to eat crow, done this a few times where I forgot to connect maybe one of the connectors and had to tear it apart again in order to see what I did, and a connector was off or loose. But led tester will show short on the line if so.Comment
-
Yea the power line. Disconnect it from PSU when testing.Comment
-
The 1000v 333j should be a good candidate to install.Comment
-
Ya these TCL's are very temperamental lol. Done several of them all sizes. Right now working on a TCL 43 Inch 43S446-CA 4K Google Smart TV works great but no backlight and panel is ok. Model only has one led strip.Tested backlight and all leds individually and they are ok. Only has one LED strip 21 x (6V Leds) running at 5.238 Volts each. Measures total 110 Volts powering leds on tester. I powered the backlights seprately with my tester and everythings working when viewing tv on and watching .. but if I power the leds from the power supply board normally the screen just does not light up. So I suspect the power supply is culprit. They are made of really cheap short life components. Ordered one from aliexpress for 22.00 and hopefully solves issue. Will post back when it arrives.Comment
-
LEDs if they are direct or edge one.. special if edge one with double LED as the case of @tech9pc ... these units build in protection zener diode.. with LED tester tjey will lighting however if the zener shorted or open.... with original PSU they will not--- so don't trust the test only by light... use yours DM in diode mode to check if there zener Diode build inComment
-
Hi Diah yes you are right thanks for your advice my friend. It's just going to cost more for diodes and stuff like 15.00 or more. I figured I might as well just order the whole power supply for only 22.00 and won't have to screw around removing capacitors and diodes etc. But I will try to repair the old one. Apparently these diodes on power board crap out frequently. Diodes Schottky SB5200, MBR3200 diode. I will see if I can find some off some old boards.Comment
-
Oh ok thanks for that advice. I did not know about that zener diode protection. Thanks Diah! wonderful advice. I will have to check that out. I will wait for the new board anyways to see what happens, before ripping it all apart again lol.Comment
-
Well thats a $200 lesson for my first TCL backlight replacement. Though I wonder why the screen is still blank? I was just going to use it in the shop but its still not showing a picture.Attached FilesComment
-
-
You got new PSU and lights show up now? Cracked screen only sometimes shows picture, not always.
Poor tv, been there done that. I personally take the TV down to the bones again and practice my disassemble when this happens. Take the new lights back off. save for next tv.
$200? What did you buy it for.Comment
-
This is A2289, board 820-01987-A. It came in with the screen not working. We could not see any image on the screen, so we ruled out a backlight issue and instead replaced the panel. The display now comes up, but no backlight.
I didn't see any signs of liquid damage, but there was some odd looking spots around U8400. F8400 has voltage on either side of it, and I have 5v present on R8444 and R8445. I did not have 3.2v at R8442 so I figured U8400 was bad, and I replaced it. After replacement, a brief probe to R8442 showed 3.2v so I assumed I had fixed the device. After reassembly however,... -
Hi, This model has bottom mounted leds . Got it with right ride 1/3 of the display black. So I checked the 6 + and - wire that powers 6 different zones and found that the 5th zone was open, which opens 6th zone too makes the right 1/3 of the display dark. Opened it and found one blown led on the 5th zone and shorted that path using solder. So now all the zones works when I check it using the bl tester , but when I put everything back together there is no backlight! The voltage I am getting when neg to chassis is 387v. How does that happen? Still individual zones working with bl tester .
... -
this tv is throwing me for a loop. do samsung tvs no longer have the backlight self test feature built into the power supply?
i tested the backlight with my LED tester and it lights up both strips. one of them reads 100v and the other reads 63.7v.
unplugged mainboard from power supply but left backlight plugged in, and then plugged psu wall power in. expected to see backlights light up but see nothing.
according to how ive diagnosed in the past, this would almost always be a bad power supply. replacement power supply was cheap like 20$ from ebay. but still i get not even... -
Hello Sharp TV experts
Our Sharp LC-80LE642U displays one short one long flash error code which is a backlight error. I went into service mode and there were 8 lamp error counts recorded. I reset the count to 0 and did a reset. The last monitor error cause was 16 B00014639:12. 16 is the code for backlight error. I tried to power the tv up but went back into error mode.
> I checked voltages on the power supply board and they all check out .. including 3.28 volts at the error pin.
> There is power to the cpu and T-CONN and no faults found there. The cpu has a flashing...01-24-2025, 11:51 PM -
Hello, I have an "ASUS ROG Strix G713QR" laptop, and for approx. 3 months I have the following problems:
1. Laptop keyboard doesn't work
2. The backlight on the laptop keyboard doesn't work
3. The x2 side LEDs (red) on the laptop don't work
The power button works, the touchpad works, and all the USB, HDMI, Ethernet, etc. ports work.
I already tried to reinstall all the drivers and reinstall Windows. So I don't know what to try anymore that is software-related.
But I am strongly aiming that it is somehow a BIOS-related problem,...
Comment