Samsung LN40B650 Standby light on, won't turn on

[Tiezane]

Hi folks,

First time posting here. Trying to make ends meet for my family, and have some fun, so I started finding broken TVs on craigslist that I might be able to repair and resell. I picked up an LN40B650 that will not power on, the Standby LED comes on solid red when plugged in, and the TV does not respond to the remote or the power button. The guy who sold it said one day it just failed to turn on. I've opened it up and checked a few things, none of the caps are swollen as far as I can tell, but the bottom of the two 450V caps made me curious. I've checked both the fuses on the PSU and they are fine, I've checked all the diodes and resistors, and they seem fine as well. Since I am so new to this, I'm not really sure where to go next, but I'm open to direction The power supply board is labeled BN44-00264A. I've included some of the pictures I've taken, please let me know what else you might want to see. I should also note, the only tools I have available are a digital multimeter that does not include a capacitor test feature, a soldering iron, standard tools like screwdrivers, my brain, and a willingness to learn. I've also included a schematic I found for the PSU board.

[capkid]

Re: Samsung LN40B650 Standby light on, won't turn on

The two 450V caps look fine to me, but that doesn't mean they aren't bad. Can you post a pic of the whole circuit board layout?

Edit: What are your voltages at the CNM802 connector on the output side of the power supply? The good thing is that you have standby power. My first thought is that your main board is bad, but it will take more testing to make a solid determination.

[beano]

Re: Samsung LN40B650 Standby light on, won't turn on

I have the Same problem let me know if you find anything I will let you know if I do

[Tiezane]

Re: Samsung LN40B650 Standby light on, won't turn on

Here's two pics of the power supply board (front and back) and the mainboard (also front and back). In both cases, the boards were flipped top to bottom, relative to the picture orientation, to get the pictures of the backsides. Let me know if there are any areas of interest you need a closer picture of.

[capkid]

Re: Samsung LN40B650 Standby light on, won't turn on

ok, can you post a pic of the whole back of the TV with the cover off? Also, please post voltage measurements at the CNM802 connector when you have them.

[Tiezane]

Re: Samsung LN40B650 Standby light on, won't turn on

ok, can you post a pic of the whole back of the TV with the cover off? Also, please post voltage measurements when you have them.

I can post a little later, what spots do I need to check voltages at? That's one of the things I wasn't sure of. I have to wait until after my girls go to bed so little fingers don't try to grab high voltages

EDIT: just saw your earlier request for voltages on CNM802. newbie question, connect to one of the ground pins on there and just check the other pins, or should I be using the chassis as ground?

[capkid]

Re: Samsung LN40B650 Standby light on, won't turn on

I can post a little later, what spots do I need to check voltages at? That's one of the things I wasn't sure of. I have to wait until after my girls go to bed so little fingers don't try to grab high voltages

EDIT: just saw your earlier request for voltages on CNM802. newbie question, connect to one of the ground pins on there and just check the other pins, or should I be using the chassis as ground?

Chassis ground.

[Tiezane]

Re: Samsung LN40B650 Standby light on, won't turn on

CNM802:
1 PWR-ON/OFF .793V
2 H_Sync 85mV+
3 STBY5.3V 5.21V
4 GND
5 GND
6 GND
7 13V(5) 12.54V
8 13V(5) 12.54V
9 GND
10 GND
11 GND
12 GND
13 5.3V 5.21V
14 5.3V 5.21V
15 5.3V 5.21v
16 5.3V 5.21v
17 GND
18 GND
19 13V (M) 12.54V
20 GND
21 13V (M) 12.55V
22 13V (M) 12.54V
23 Inv_ON/OFF 2.9V
24 N.C.
25 E-PWM 4.94V
26 GND
27 DET_5V 4.96V
28 N.C.
29 N.C.
30 N.C.

With the cable disconnected from CNM802, when I applied power the backlight immediately came on. I tried with that cable connected, and the cable to the T-Con disconnected, and it did NOT light up. I also tried with everything but the connection to the front buttons panel connected, and got nothing, EXCEPT...I tested each pin on CN1601, and got nothing. I accidentally connected pins 1&2, and the backlight came on, and stayed on as long as the pins were connected. When the connection was broken, the backlight turned off. CN1601 is the longer connector at the bottom of the mainboard. I'm thinking the voltages all look like they are reasonable, the only anomaly was the H_Sync voltage. It started low and kept climbing, over the course of 30 seconds or so, it got up to 85mV and seemed to be still climbing slightly, I don't know if that is normal or not. That would lead me towards thinking the mainboard is the issue, not the PSU. Let me know what you think, and if there are any other measurements you would like to see still.

[budm]

Re: Samsung LN40B650 Standby light on, won't turn on

The main board will need more in depth troubleshooting, you can start by testing the voltage regulators and the switching supply on the main board, try to locate the main board diagram. Also look to see how much the replacement board will be.
The "PWR-ON/OFF .793V" should be around 1.5V or more when you switch on the TV, it is generated by the main board.

[Tiezane]

Re: Samsung LN40B650 Standby light on, won't turn on

The "PWR-ON/OFF .793V" should be around 1.5V or more when you switch on the TV, it is generated by the main board.

Can you elaborate? The only way I was able to get a reading at that pin was to disconnect the white cable connecting the mainboard on the left to the power supply, and touching the pin directly inside the socket. Is there a different way I should have tested that pin?

The main board will need more in depth troubleshooting, you can start by testing the voltage regulators and the switching supply on the main board, try to locate the main board diagram. Also look to see how much the replacement board will be.

Replacement main board is $75+. I've been trying to find the diagram for the main board, but my searches are coming up with nothing. If anyone else has/knows where to find it, that would be appreciated. This is apparently the same main board used in all the LN**B650 models. I found a link to someone with an LN40B630 with a similar problem, and someone there suggested resetting the EEPROM (see: This link) might be helpful, is that something that would be recommended here? If so, can anyone identify which chip on the main board is the EEPROM? I'll keep looking for that diagram to see what we can find. Thank you for all the help so far folks!

[capkid]

Re: Samsung LN40B650 Standby light on, won't turn on

What's the part number on your main board?

Edit: Never mind. I was able to enlarge the pic to see BN94-02673F and BN41-01149A.

[budm]

Re: Samsung LN40B650 Standby light on, won't turn on

"Can you elaborate? The only way I was able to get a reading at that pin was to disconnect the white cable connecting the mainboard on the left to the power supply, and touching the pin directly inside the socket. Is there a different way I should have tested that pin?" Take the reading with all the connectors conneted.
You have already verify that the power supply and the Inverter circuits are working by disconnecting the cable between the main board and the power supply board then the backlights come on when you apply the power to the TV.

[Tiezane]

Re: Samsung LN40B650 Standby light on, won't turn on

Take the reading with all the connectors conneted.
You have already verify that the power supply and the Inverter circuits are working by disconnecting the cable between the main board and the power supply board then the backlights come on when you apply the power to the TV.

I guess what I was trying to ask was what would be the best way to test with the connectors connected. From looking at this thing, I think the only way to do that would be to unscrew the mainboard, and access the back of it while plugged in to get to the matching pin there (the one on the back of the power supply isn't reachable with the cable plugged in.) Anyway, if you say it's all good, I won't worry about that one

[truep]

Re: Samsung LN40B650 Standby light on, won't turn on

I have the same TV on the wall in my bedroom! I bought it for $25 because it wouldn't power on. I ended up replacing the main board. I let it sit until I finally found on for $45.
It's a great TV and well worth the replacement cost of a new main. Just be sure the numbers match exactly (BN96xxxxx or BN41XXXX).

[Tiezane]

Re: Samsung LN40B650 Standby light on, won't turn on

Just be sure the numbers match exactly (BN96xxxxx or BN41XXXX).

I was curious about that, I've seen a lot of sites that have what appear to be replacement part numbers, but there seem to be 3 or 4, and if you search for those, there's another 3 or 4 that come up and ow ow ow my head.....


I'm still hoping we can find a diagram of the board, and see if there's anything I can replace to get it working again without buying the whole board. If not, $45 is pretty reasonable, and I did find some online last night that I'm keeping an eye on. I just figure if I can try to replace something on that board, the worst that can happen is I fail and have to buy a new board anyway.

[Tiezane]

Re: Samsung LN40B650 Standby light on, won't turn on

I have the same TV on the wall in my bedroom! I bought it for $25 because it wouldn't power on. I ended up replacing the main board. I let it sit until I finally found on for $45.

Found the board on eBay, also for $45, should be here by Saturday, eBay says. I'll swap it in and see what happens. I'd still like to try to figure out what may have died on the mainboard, so I can try to repair it in case the new one ever goes bad, I have a backup

[Tiezane]

Re: Samsung LN40B650 Standby light on, won't turn on

I finally managed to find a service manual, it covers the ln40, 46, and 55B650 models. It looks like the EEPROM is IC112, but in talking with another person on the phone, the manual he had showed it might be IC1201 or IC1603. It's a 24C02 EEPROM. I'm going to look for it tonight, and see if I can try the forced reset of the eeprom to bring this thing back to life at all. At this point, the worst that happens is... nothing and I have a new board coming anyway. I think I found IC1201 on the pictures I posted, but it's hard to tell. It's definitely an 8pin chip right below the HDMI 1 port, and above the RCA input block. I'll post later with results. Uploading the manuals for anyone else who needs them. The Disassembly & Reassembly, Product Specification, and Troubleshooting PDFs are too big to upload. Relevant ones attached.

[Tiezane]

Re: Samsung LN40B650 Standby light on, won't turn on

Finally got around to trying the EEPROM reset... and I can't find the EEPROM. IC1201 and IC1603 are not the right chips, they were marked ATMLH842 and ATMLH852 respectively. Could not find IC112 or a 24C02 anywhere on the board, and I went over it with a magnifying glass and a flashlight, and triple checked every 8-pin IC I could find. guess I'm just going to have to wait for the new board to arrive.

[martino]

Re: Samsung LN40B650 Standby light on, won't turn on

On my samsung(different model tho) I couldn't find the eeprom either.
Had to remove the mainboard and on the backside of the board I found these "test points"..I soldered wires on them so that I could connect them with mainboard installed in tv...

[Tiezane]

Re: Samsung LN40B650 Standby light on, won't turn on

I'll have to pop the board off again and look for those. It was late, I was tired, and trying to find it with a flashlight and a magnifying glass. Do you have a model # for your board by any chance?