Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Troubleshooting TVs and Video Sources
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 02-06-2021, 01:59 AM   #1
Chrille
Chrille
 
Join Date: Feb 2021
City & State: Skillingaryd
My Country: Sweden
Line Voltage: 230VAC 50Hz
I'm a: Knowledge Seeker
Posts: 21
Default Samsung LE40A676 takes several minutes to start

Hi,
I have a Samsung LE40A676 with the same phenomena as these posts:

https://www.badcaps.net/forum/showthread.php?t=73891
https://www.badcaps.net/forum/showthread.php?t=45913

Blinking red LED and several minutes to start up.
I have checked the PSU board and there's no visibly bad caps. I have also measured all caps on the PSU board an they all seem to be Ok, just to be shure.
Does any one know if there's a "bad C102" or similar on this main/video board to replace, as the talk about in the linked threads above?
I can't see any caps that looks bad or anything else that not looks as it should.

(I'm sorry if you find this post in another thread but I wasn't able to remove my other post)
Attached Images
File Type: jpg 20210205_202814.jpg (1.59 MB, 22 views)
File Type: jpg 20210205_202832.jpg (1.76 MB, 18 views)
File Type: jpg 20210205_202859.jpg (1.86 MB, 19 views)
Chrille is offline   Reply With Quote
Old 02-06-2021, 10:31 AM   #2
nomoresonys
Badcaps Veteran
 
Join Date: Jan 2013
City & State: midwest
My Country: U.S.
I'm a: Knowledge Seeker
Posts: 6,459
Default Re: Samsung LE40A676 takes several minutes to start

Start with testing the voltages at the connector on the powerboard the one with the cable that goes from powerboard to mainboard on powerboard side, with EVERYTHING hooked up, you measure them with your mutimeter, set meter to 20 vdc then report them, put neg probe on chassis metal ground, pos probe on pin of connector, measure in standby take note, leave probes where they are then power on tv and again take note of voltages, report them here, example pin 1-ps-on-0 volts standby-power on-3.3 volts. This is how we see what voltages you do or don't have.
__________________
Signature: Any Stooge can find an "Idiot" by looking in his mirror.
nomoresonys is offline   Reply With Quote
Old 02-06-2021, 04:53 PM   #3
Chrille
Chrille
 
Join Date: Feb 2021
City & State: Skillingaryd
My Country: Sweden
Line Voltage: 230VAC 50Hz
I'm a: Knowledge Seeker
Posts: 21
Default Re: Samsung LE40A676 takes several minutes to start

Hi,
Thanks for your reply!
All voltages seem to be Ok
Pin 1 is 3.69V (Power on)
Pin 2 is 5.0V
Pin 3 is 5.11V (should be 5.3V) Ok
Pin 7,8 is 12.97V (Should be 13V) Ok
Pin 13-16 is 5.07V (Should be 5V) Ok
Pin 19, 21, 22 is 12.96 (Should be 13V) Ok
Other pins are GND on N/C

The power goes up and down in interval.
The interval is 15s high (power on) and 5s low (power off). I get the feeling that it tries to start but fails.
Chrille is offline   Reply With Quote
Old 02-06-2021, 07:12 PM   #4
nomoresonys
Badcaps Veteran
 
Join Date: Jan 2013
City & State: midwest
My Country: U.S.
I'm a: Knowledge Seeker
Posts: 6,459
Default Re: Samsung LE40A676 takes several minutes to start

Check all the diodes on the powerboard.
nomoresonys is offline   Reply With Quote
Old 02-07-2021, 09:35 AM   #5
Chrille
Chrille
 
Join Date: Feb 2021
City & State: Skillingaryd
My Country: Sweden
Line Voltage: 230VAC 50Hz
I'm a: Knowledge Seeker
Posts: 21
Default Re: Samsung LE40A676 takes several minutes to start

Yes, all diods checked and they are all Ok.
Since all voltages from the PSU board seems to be Ok and the power is shut of from the mainboard, I would guess the problem is on the main board?
The attached image shows the red power on signal (pin 1) and the yellow is the 13V output (pin 7) from the PSU board.
Here we can see that the power-signal goes low befor the 13V starts to drop.
Attached Images
File Type: jpg 20210207_162229.jpg (1.72 MB, 16 views)
Chrille is offline   Reply With Quote
Old 02-07-2021, 09:55 AM   #6
yokoono
Badcaps Veteran
 
Join Date: Apr 2010
Posts: 226
Default Re: Samsung LE40A676 takes several minutes to start

I did not see specified if the backlight lights up. Unplug the power cord between the power supply and the main and see if the backlight up and stay lit.
On many Samsungs the control for power and backlight is done with "-" (ground) not "+". Power supplay gives a positive voltage to the respective pins for starting but the processor is the one that keeps the pins on the ground.

Last edited by yokoono; 02-07-2021 at 10:02 AM..
yokoono is offline   Reply With Quote
Old 02-07-2021, 11:26 AM   #7
Chrille
Chrille
 
Join Date: Feb 2021
City & State: Skillingaryd
My Country: Sweden
Line Voltage: 230VAC 50Hz
I'm a: Knowledge Seeker
Posts: 21
Default Re: Samsung LE40A676 takes several minutes to start

If I unplug the power cord to the main, the PSU won't start because it will not get a "start signal" from the main board... (?)
Anyway, the backlight does not seem to light up. I measured the voltage on, what I think is the backlight cable/connector, and it was zero (during the "try-to-start-up-sequence" with every thing connected).
On my PSU-image above, it's the light-blue and white cable in the left lower corner of the image, beside the two transformers.
Chrille is offline   Reply With Quote
Old 02-07-2021, 11:55 AM   #8
R_J
Badcaps Veteran
 
Join Date: Jun 2012
City & State: ☻
My Country: Canada
I'm a: Professional Tech
Posts: 6,979
Default Re: Samsung LE40A676 takes several minutes to start

This power supply does not have built in pullup resistors like other Samsung power supplies.
This power supply requires +5.3v standby connected to Power on/off to turn ON the power supply (it has a built in 4.7k series resistor RM837) to protect QM807 (on/off transistor)
To turn on the backlights you need to supply +5.3V standby to pin 1 of CNl803 (inverter On/Off) (has built in 1k RI801 series res.)
Both CNI803 and CN801 cables need to be disconnected to protect the main board.

Last edited by R_J; 02-07-2021 at 11:58 AM..
R_J is offline   Reply With Quote
Old 02-07-2021, 12:51 PM   #9
Chrille
Chrille
 
Join Date: Feb 2021
City & State: Skillingaryd
My Country: Sweden
Line Voltage: 230VAC 50Hz
I'm a: Knowledge Seeker
Posts: 21
Default Re: Samsung LE40A676 takes several minutes to start

Ok, but haven't we already found that the backlight doesn't work/light up?
When the PSU starts for 15s, there is no power on the backlight connector witch I guess it should have?
Or is the backlight power controlled separately?
(I guess the image shows the backlight cable/connector, right?)
Attached Images
File Type: jpg 20210207_194824.jpg (1.23 MB, 10 views)

Last edited by Chrille; 02-07-2021 at 12:53 PM..
Chrille is offline   Reply With Quote
Old 02-07-2021, 01:28 PM   #10
R_J
Badcaps Veteran
 
Join Date: Jun 2012
City & State: ☻
My Country: Canada
I'm a: Professional Tech
Posts: 6,979
Default Re: Samsung LE40A676 takes several minutes to start

The voltage on THAT connector is likely around 3~5KV at 60khz, what are you using to try and measure it? That connector feeds a distribution board and the ccfl's, If there is a problem ie: bad connection, bad transformer, bad ccfl etc. the backlight will detect the error and will shut down.

Last edited by R_J; 02-07-2021 at 01:32 PM..
R_J is offline   Reply With Quote
Old 02-07-2021, 02:21 PM   #11
Chrille
Chrille
 
Join Date: Feb 2021
City & State: Skillingaryd
My Country: Sweden
Line Voltage: 230VAC 50Hz
I'm a: Knowledge Seeker
Posts: 21
Default Re: Samsung LE40A676 takes several minutes to start

I guess I should get something here if it's 3~5KV 60khz but the frequency might be too high...?
(I had to zip the movie to be able to attach it)
Attached Files
File Type: zip Movie.zip (6.03 MB, 9 views)
Chrille is offline   Reply With Quote
Old 02-07-2021, 02:36 PM   #12
R_J
Badcaps Veteran
 
Join Date: Jun 2012
City & State: ☻
My Country: Canada
I'm a: Professional Tech
Posts: 6,979
Default Re: Samsung LE40A676 takes several minutes to start

Quote:
Originally Posted by Chrille View Post
I guess I should get something here if it's 3~5KV 60khz but the frequency might be too high...?
(I had to zip the movie to be able to attach it)
You can't use that to work on electronics, it is for detecting line voltage. You need a dvm or multimeter.
R_J is offline   Reply With Quote
Old 02-07-2021, 02:44 PM   #13
Chrille
Chrille
 
Join Date: Feb 2021
City & State: Skillingaryd
My Country: Sweden
Line Voltage: 230VAC 50Hz
I'm a: Knowledge Seeker
Posts: 21
Default Re: Samsung LE40A676 takes several minutes to start

I have that as well but it can't measure 3~5KV (See previous results)
Chrille is offline   Reply With Quote
Old 02-07-2021, 03:32 PM   #14
R_J
Badcaps Veteran
 
Join Date: Jun 2012
City & State: ☻
My Country: Canada
I'm a: Professional Tech
Posts: 6,979
Default Re: Samsung LE40A676 takes several minutes to start

Slightly unplug the connector going to the HV distribution board (leave the plug in the connector but allow about 1/8" of distance between the contacts) and see if you get some arcing when first turned on. That will tell you if the high voltage section on the power supply is working
I would also remove the black shield from the inverter dis. board and inspect the connections and transformers for each ccfl. You can leave the plastic off but reinstall the ground screws.

Last edited by R_J; 02-07-2021 at 03:52 PM..
R_J is offline   Reply With Quote
Old 02-08-2021, 12:55 PM   #15
Chrille
Chrille
 
Join Date: Feb 2021
City & State: Skillingaryd
My Country: Sweden
Line Voltage: 230VAC 50Hz
I'm a: Knowledge Seeker
Posts: 21
Default Re: Samsung LE40A676 takes several minutes to start

Since there should be 3-5KV in that cable, I don't want to fiddle too much with that connectors when the PSU is on.
Any way, I'm pretty shure that there is no power in these cables because:

1. There is no working backlight when the PSU is active.
2. I think my electric field detector should detect it.
3. All heatsinks gets a higher temperature when the PSU has been powered on for a while but the one with the high-voltage MOSFET-drivers! (STP9NK50ZFP) This one is "cold as ice"

My question is: Should the backlight power be active when the PSU is on?
If so, there is something with the backlight power!
Chrille is offline   Reply With Quote
Old 02-08-2021, 01:09 PM   #16
dick_barton
Badcaps Veteran
 
dick_barton's Avatar
 
Join Date: Aug 2015
City & State: Cardiff
My Country: Wales
Line Voltage: 230V AC, 50Hz
I'm a: Hobbyist Tech
Posts: 6,227
Default Re: Samsung LE40A676 takes several minutes to start

Have you checked the 2nd fuse soldered on the board
What voltage do you have on pin 1 (Inverter On/Off) of CNI803 and on the remaining pins of that connector?
__________________
Willing to help but I'm no expert.

Last edited by dick_barton; 02-08-2021 at 01:16 PM..
dick_barton is offline   Reply With Quote
Old 02-08-2021, 02:42 PM   #17
Chrille
Chrille
 
Join Date: Feb 2021
City & State: Skillingaryd
My Country: Sweden
Line Voltage: 230VAC 50Hz
I'm a: Knowledge Seeker
Posts: 21
Default Re: Samsung LE40A676 takes several minutes to start

Yes, I've chacked all fuses and they're Ok.
The voltage on the inverter is 31.7 mV when the board is On/active and 3.4 mV when it's in inactive state.

(I've measured the two STP9NK50ZFP and they also seem to be Ok)

Note: This is when the TV is in the not-working-state, i.e. when it tries to power up but fails.

If I let the TV be on for, say 30+ minutes, it sudden comes to a state when it works. In that state, the inverter voltage is 4.91V.
In this state, everything works fine. The backlight is Ok. My electric-field-measure-tool (se video) indicates power in the high-voltage cables.
It's just that, that I don't really like waiting 30 minutes or more to power up the TV! Even when I was a little kid, I didn't have to wait that long!

So here's a small summary:
1. Power coord is unplugged.
2. I plug in the power coord to the wall and power on the TV.
3. The TV tries to start for 30+ minutes but fails.
4. During this time, the inverter signal goes between 3.4mV and 32mV
5. After 30+ minutes, the TV suddenly starts to work.
6. The inverter signal goes to from 32mV to 4.9V at the same time the backlight lights up. (a few seconds efter the PSU has started)
7. I can now power on and off the TV without any problems. I starts directly!

I think it's when it have been shut of a little longer the problem occur...

Last edited by Chrille; 02-08-2021 at 03:44 PM..
Chrille is offline   Reply With Quote
Old 02-08-2021, 04:01 PM   #18
R_J
Badcaps Veteran
 
Join Date: Jun 2012
City & State: ☻
My Country: Canada
I'm a: Professional Tech
Posts: 6,979
Default Re: Samsung LE40A676 takes several minutes to start

The inverter on/off signal comes from the main board so you could force the power supply on to prove the fault is on the main board
Try using a heat gun to heat areas of the main board to see if it will turn on sooner.

Last edited by R_J; 02-08-2021 at 04:30 PM..
R_J is offline   Reply With Quote
Old 02-08-2021, 05:19 PM   #19
dick_barton
Badcaps Veteran
 
dick_barton's Avatar
 
Join Date: Aug 2015
City & State: Cardiff
My Country: Wales
Line Voltage: 230V AC, 50Hz
I'm a: Hobbyist Tech
Posts: 6,227
Default Re: Samsung LE40A676 takes several minutes to start

As RJ says there appears to be an issue with Inverter On signal from the mainboard to the power supply.
dick_barton is offline   Reply With Quote
Old 02-08-2021, 06:02 PM   #20
Davi.p
Badcaps Veteran
 
Davi.p's Avatar
 
Join Date: Sep 2009
City & State: Milan
My Country: Italy
I'm a: Hobbyist Tech
Posts: 1,907
Default Re: Samsung LE40A676 takes several minutes to start

Hey, this is not the way to diagnose... first check the PSU itself by putting the right resistances on the 5,3v and 13v as dummy load, for 5,3v example a 3,3ohm 10w, for 13v 3x3,3ohm 5-10W in series, a diode (not resistor) from A5,3V to Poweron(cathode), and a jumper from poweron to BL_ON. IF the resistors warms up and tensions stays ok the PSU is OK. IF PSU seats down then you need a new PSU (i have one of this model)..

Last edited by Davi.p; 02-08-2021 at 06:04 PM..
Davi.p is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2021
Powered by vBulletin ®
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 04:51 AM.
Did you find this forum helpful?