Re: Samsung LN40B500P3F backlight won't stay on
The backlight tubes LOOK fine, at least the ends that I can see without taking the back of the TV apart part enough to expose the bulbs completely.
Is there a good way to test the bulbs? Or determine what part of the board is bad? I read a post about using an old CFL for testing. I have several of them around that work still. Which is a better test - using the old bulb circuitry to try to power the bulbs in the TV? Or trying to use the TV board to power the CFL tube?
Nexus1966
Member
Last Activity: 09-05-2016, 06:47 PM
Joined: 06-23-2016
Location: Omaha, Nebraska
-
Re: Samsung LN40B500P3F backlight won't stay on
Sorry, I was not very clear on what readings were for what output there. Here are the readings as I took them from the top of the board to the bottom along with which inverter transformer and which pins they correspond to.
1536 ohms - TI801S between pins 3 & 4
1531 ohms - TI801S between pins 1 & 2
1542 ohms - TI802S between pins 3 & 4
1541 ohms - TI802S between pins 1 & 2
1538 ohms - TI803S between pins 3 & 4
1536 ohms - TI803S between pins 1 & 2
...Leave a comment:
-
Re: Samsung LN40B500P3F backlight won't stay on
Primary is .6 ohms on all of them, but then again my multimeter shows .4 just touching the leads together, so make that .2 ohms corrected reading?
Secondary resistance starting with the top output of TI801S and then going down the board from there is:
1536 ohms
1531 ohms
1542 ohms
1541 ohms
1538 ohms
1536 ohms
1515 ohms
1514 ohmsLeave a comment:
-
Re: Samsung LN40B500P3F backlight won't stay on
I've tested all of the diodes and all of the capacitors, all seem to be OK.
I also tested the resistance on the backlight output transformers, they all are fairly close.
Could this be a bad backlight bulb or bulbs causing the issue?Leave a comment:
-
Re: Samsung LN40B500P3F backlight won't stay on
More pictures of the back side of the board...Leave a comment:
-
Samsung LN40B500P3F backlight won't stay on
I picked up a Samsung LN40B500P3F for free. It turns on for a few seconds, but then the backlight dies. It will come on again after about 5 seconds and stay on for about a second. It repeats this a few times, and then eventually the backlight stays off.
As far as I can tell the rest of the TV is working good, it is only the backlight that won't stay running.
I see there are numerous posts here about this model or similar Samsung LCDs, but it seems like most of them are completely dead and not the same issue as this one.
I get 392 volts DC across the... -
Samsung pn51f5300afxza - vertical line through screen
Is this a bad plasma panel, or is it possible that this is something worth fixing?... -
Re: Toshiba 58L4300U won't power on
My parts from Digi-Key arrived today, so I replaced the 2 diodes and the MOSFET.
Success!...Leave a comment:
-
Re: Toshiba 58L4300U won't power on
Does the diode and the MOSFET both being bad explain the issues, or might it be deeper than that?Leave a comment:
-
Re: Toshiba 58L4300U won't power on
No, neither appears to be shorted to the gate.Leave a comment:
-
Re: Toshiba 58L4300U won't power on
I found the diodes at DigiKey.
Q301 appears to be bad, at least according to the method I found on how to test with a DMM.
I removed it, shorted all the pins together, then used the diode check function on my meter with the negative on the source and the positive on the drain, I get continuity before triggering the gate.
It's part number is TK13A25, DigiKey appears to not have them. Checking around for a replacement now.
Edit - DigiKey suggests 497-12570-5-ND as a replacement.Last edited by Nexus1966; 06-25-2016, 04:24 PM.Leave a comment:
-
Re: Toshiba 58L4300U won't power on
Looks like D201 is a schottky also. It appears to test OK, but I only have a cheap analog meter with a 1K ohm setting, no 10K option. But I get full scale one way, nothing at all the other way. I'm assuming D201 is good.Leave a comment:
-
Re: Toshiba 58L4300U won't power on
So knowing that one of those schottky diodes is bad, what else should I examine?Leave a comment:
-
Re: Toshiba 58L4300U won't power on
Yes I did remove them both from the board to test after my initial test showed them shorted both ways.Leave a comment:
-
Re: Toshiba 58L4300U won't power on
I started just testing random components and found what looked to be a shorted diode.
D301A or D301B (they are in parallel) - a google search of the part number brought me to this: [url]http://www.vishay.com/diodes/list/product-89144/[/url]
According to that page it is a schottky diode. I got an analog multimeter to test them with the instructions I found here: [url]http://www.electronicrepairguide.com/schottky-diode.html[/url]
One of them appears to test good, the other one is shorted both ways.Re: Toshiba...Leave a comment:
-
Re: Toshiba 58L4300U won't power on
Well, I did it.
I didn't know what voltage the LEDs need, so I didn't connect them yet. But I wired up a computer power supply, and confirmed the TV works, minus the back-light. The main board appears to be OK. I plugged in a Fire TV stick and if I shine a flashlight on the screen, I can see the menu from it and it looks good, aside from being really dim of course.
So... do I try to McGyver this with an external power supply, or do I fix the original power supply? I could just start randomly replacing components on it...Leave a comment:
-
Re: Toshiba 58L4300U won't power on
Thinking outside of the box a little here... would it be possible to hook up a computer power supply to run this TV? I know the main board only needs 12 volts and 5 volts, a computer power supply provides both. What voltage would the LEDs need?
Assuming I can wire up a computer power supply to send the right voltages to the right places, that would allow me to verify the status of the main board right?Leave a comment:
-
Re: Toshiba 58L4300U won't power on
I would probably buy a new power supply board at this point if I found a reasonably priced one, but I can't seem to even find any replacements that are in stock. Seems like this must be common failure, I found a few places selling them and they are all out of stock.
Is it worth trying to repair this board?Leave a comment:
-
Re: Toshiba 58L4300U won't power on
I managed to find this post which looks like the same power supply and same type of problem:
[url]https://www.badcaps.net/forum/showthread.php?p=615403#post615403[/url]Re: Toshiba 58L4300U won't power on<...st615403[/url]Leave a comment:
-
Re: Toshiba 58L4300U won't power on
At those caps I get about 1.8 volts when first switched on, then it quickly drops to almost nothing.Leave a comment:
No activity results to display
Leave a comment: