Samsung 46" red standby light ok, but not turning on

[edy]

Hi folks,

I found a Samsung 46" dumped on the side of the road. Missing remote, most of the screws were off the back... looked like someone had a go at it (at least looked at it on the inside but doesn't appear to have done anything). The panel looks in good shape as does the case, so whoever looked at it probably didn't do much other than open it and give up.

I popped the hood and could not see any obvious damage, caps look ok but I know that is not a reliable test. I have a cap tester and will have to check them. Plugged in the TV, the red "standby" light goes on. Tried the buttons on the front panel but they didn't do anything. Just in case the touchpanel was a problem, I tried using a universal remote as well as a couple of my other Samsung TV remotes (I have a few circa 2009 which is the age of this TV)... Did not power on, and nothing made the red standby light even blink.

So first obvious question, is this a CAP issue on the main power supply? Seems like the easiest thing to do is to simply test and replace all the caps (the 2 large ones, 5 medium and 4 small ones) and see how it goes. I've done that on a few other TV's, an XBox, an LCD monitor and it has fixed them.

My main family TV is a Samsung 42" from around the same time (2007) and I had to change 2 caps on the main power board around ~2010-2011 and it is still working now 10 years later. If can get this 46" to work I can replace our family TV with this bigger one. When my 42" Samsung failed, it had a standby light and would turn on but click and blink the red light but the screen would take minutes to turn on, until eventually it didn't want to power up. But at least it "tried" to boot up (some activity).

Whereas this 46" TV doesn't show any indication of even responding.... so could it still be a simple Cap issue? On this TV the front-panel buttons (I assume some kind of "touch sensitive" panel) as well as a few Samsung and Universal Remotes I tried did not seem to create any response, no red standby light blink. So is it a CAP issue or something with the micro handling the power on routine? What should I be doing first?

I've attached lots of photos which may help, which I'll span across 2 emails due to file size restrictions per post.

[edy]

Here are a few more photos. As you can see, the TV looks like it is in pretty good shape. I've included photos of the back of the TV, close ups of the orange power supply and the green control/processing board. Connected to the green processing board is a small board with an infrared sensor (for the remote) and then the long touch-panel board that has the buttons for power, channel, source, menu, etc.

Any help or service manual link to get started with this repair would be helpful. Thoughts, suggestions all helpful but I have a feeling the easiest thing to do would be to pull out that power board and go ahead and test and replace the caps. What do you think?

[retiredcaps]

If your standy led is on, you are likely getting 5V standby.  Verify with your meter that is is close to 5VDC and steady.

On CN801, see if there is a pin marked PWR_ON.  This is usually generated by the green logic/main board when the TV is told to power on.  It is likely 0V when off, and maybe 3.3V when instructed to turn on.

[retiredcaps]

BTW, this TV is likely documented over at badcaps.net.  I don't participate in the fix TV forum anymore, but I will guess this model has been covered there already.

Despite its website name, it is just more than bad caps.  People there can help fix component level problems other than bad capacitors.

[Bud]

This may be a tedious job. The main board has secondary dc/dc power converters , you may need to check them all. This may not be easy because their Enable signals may be chained or are controlled by the MCU. You really need to find the schematic for the tv. For an easier way try looking on ebay for the main and ps boards, sometime people sell them when their tv lcd panel gets damaged.

[edy]

Thanks for the help and suggestions. The model number just to be sure is:  LN46B610A5FXZC.

A check over at ShopJimmy.com and also by reading the print on the boards suggests the power supply board is: BN44-00265B

http://www.shopjimmy.com/samsung-bn44-00265b-power-supply.htm

And the logic board is: BN41-01149B (ShopJimmy subtitute is BN94-02621E, I've also seen BN94-03140F)

http://www.shopjimmy.com/samsung-bn94-02621e-main-board-for-ln46b610a5fxza.htm

I managed to locate the power supply board schematic. Meanwhile I'll look for the logic board schematic. Hopefully this will help in the meantime! Download from there (15 MB file):

https://ia601200.us.archive.org/13/items/Samsung_BN44-00265B/Samsung_BN44-00265B.pdf

[edy]

A few suggestions from some threads over at Badcaps.net suggest the following:

Thread: https://www.badcaps.net/forum/showthread.php?t=34662&highlight=BN41-01149B

OK, the power supply-inverter board has built-in pull up resistors for the PS_ON and the BL_ON, so disconnect the cable between the power supply and the main board, the backlights should come on when you APPLY 120VAC to the TV.

So I assume they mean to disconnect the long cable (the black ribbon cable) that connects the logic board to the power supply will cause the logic board to stop telling the power board to keep off and plugging it in will cause the backlights to turn on the minute I plug the TV into an outlet?

Assuming the backlights do turn on, they suggest:

First, check the power supply output voltages - 13V and ~5.4V - are OK.
To do this, place your probe on the pin corresponding to that voltage with the connector out. (TV powered on - backlight working. Do not touch any part of power board!) Note voltages. Then, turn power off, plug in main board connector, and check voltages again in a similar manner. (Press probe onto join where sheath and wire meet, it's a few mm in.) Note voltages.

...and...

I do believe a shorted T-con could also stop the Tv from switching on, I would hook it all back up again but this time disconnecting the T-con from the main board(it's the board sitting at the bottom), see if it powers up after doing so.

There is another good thread here on the same issue as my TV:

https://www.badcaps.net/forum/showthread.php?t=56560&highlight=BN41-01149B

Someone in that thread listed the pin outs from the power board to be the following voltages:

Pin readings when power supply is NOT plugged into main board (Only even pin#'s with a wire connection is Pin#2 and Pin#30):
1 POW ON/OFF: .800V
2 H_SYNC: 4.1mV
3 STB 5.3V: 5.33V
4~6 GND: 0
7~8 13 VS: 13.07V
9~12 GND: 0
13~16 5.3V: 5.33V
17~18 GND: 0
19 13Vm: 13V
20 GND: 0
21~22 13Vm: 13V
23 INV ON/OFF: 5.25V
24 NC: N/A
25 E-PWM: 5.33V
26 GND: N/A
27 DET_5V: 5.33V
28~30 GND: 0

So question is, if I want to check my power board pins how do I go about actually using my multimeter? I assume I would set it to DC volts auto and connect the black probe to one of the ground pins (seems like there are many) and then use my red probe to touch the various other pins that should have a voltage and see the reading I get? Is this the only way? Seems like it may be difficult getting in there with the probes and that I may accidentally short 2 adjacent pins together through the probe... I don't want to damage anything. Any suggestions?

NOTE that these same pin-outs appear in my PDF schematic that I linked above. So do I put my black probe to say one of the GND pins (e.g. 28-30) and then touch the tip of the red probe to all the other pins starting from #1 and see what voltage readings I get off each pin?

[vinceroger]

Hi im a member on bad caps yes when you disconnect the cable between the power supply and the main board the backlights should come on so try this test first as you should also see if the lcd screen is ok too and not smashed etc.
Regarding the voltage readings on the hot side of the psu i use the negative side of one of the filter capacitors (laid on there sides) as my ground but on the secondary side i use just a screw mounting point ft metal tv chassis as a ground and yes just then slide the red probe down the side of the wire you want to test the voltage of.

[edy]

Hi folks,

I disconnected the logic board from the power supply and the backlight did power on, allowing me to view the display. Unfortunately, I see some lines on it that probably make the set unwatchable for normal use (see attached images). However, as a learning exercise I still want to try and get this thing up and running (as long as it doesn't cost me much) just to learn more trouble-shooting exercises.

First, I am not sure how the LCD matrix works exactly and what would cause the pixels to be lighting up this way. Second, the TV still doesn't power up so there is something else going on. Third, once the TV turns on and runs a bit with cycling images, could some of these lines possibly disappear (perhaps I'm being too optimistic)? This happened to my older laptop (see this thread: https://www.eevblog.com/forum/repair/laptop-screen-issue-help-diagnoserepair-needed!/msg936867/#msg936867) and the lines did in fact disappear.

Can someone please explain the way the matrix works. Thanks. Is it like a Charlie-Plexing type situation where there are (for example) column "sources" and "drain" rows that are cycled at very high speed to essentially access each and every LCD element in the display at 30 frames per second? Or is the screen broken up into much smaller "screens" in a sense, with each of those subscreens working this Charlie-Plexed way?

Ok, so what next? Am I to check voltages coming off that black ribbon cable? How do I do so safely without shorting adjacent pins? Can I just use the ground of one of the ground pins on the same cable (there are many pins that are GND) to compare voltages to? I'd rather not clip on to a capacitor if I don't have to.

[edy]

Notice the lines don't go all the way up the screen vertically. Most of the issues I've seen with vertical lines on panels involves the entire column. If the screen is black that means the individual LCD elements are being turned on, and areas where light makes it through are "off" or not getting voltage? Since the logic board is getting no power, what is driving the LCD panel at this point and could it be traced to an electronic component or do you think there is unrepairable physical damage to the panel? Still, if I can get the display to run this may not be that distracting, and either way I want to try to trouble-shoot the other issue which is failure to power up.