Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board
Summary for TL-DR readers:
• Backlight is intermittent, may come on with TV boot or not. No flickering, never fails during TV on.
• Have obtained Samsung schematic & service documents - Can upload if helpful.
• Have read ALL applicable threads
• C1818 and CP820 replaced as low hanging fruit
• CN802 data taken for normal and failed BL operation. SUMMARY: Pin 2 - 5vDet = 3.52 @normal, 0.0 @BL fail. Pin 6 - EPWM = 1.631 @normal, 1.058 @BL fail.
• VCC pin (18) of PFC ICP801 is 5.17 & Vin (Pin 1) is 11.03 when the BL is lit, no failed data yet.
• VCaps CP802/803 = 385V @BL on, 149.9V @fail BL, ~159 @TV off
• Transformer “T1802S White” squeals during boot, shorter time when BL fails.
• Voltage across C1842 = .599V when the BL fails. Under voltage lockout?
The rest of the story:
To set a baseline, I have read all the BN44-00341B and LN46C630K1F threads, obtained the circuit diagram for BN44-00341B, obtained the Samsung Fast Track Troubleshooting Manual and Samsung (Service) Training Manual for the TV, the latter two from Elektrotanya BTW.
Symptoms: In normal use, the backlight may fail to come on when the TV is started. It can repeat for numerous re-starts, this is the detail of the problem I started with so I dug in and started to troubleshoot. The rest of the TV works (sound etc.).
On bench test sometimes the backlight will fail several times in a row then work. It can (only) sometimes be provoked to fail by unplugging while the TV is on and plugging back in. If the TV has been unplugged while on it starts up (boots) on its own when the plug is inserted.
On the bench it may not fail for many repeats of re-start which is maddening when you want to take some data while the backlight is failed!
I read about the C1818 and CP820 failures so even though they didn’t look failed I took an initial grab for low hanging fruit and replaced them, OK for a while but the BL failed to light again a few days later – basically back to the same symptoms proving that the caps were not failed. That led to a thorough reading of all the applicable threads and where I am today.
I have read BUDM’s comments about drift of the four 1.5M SMT resistor chain (RP 802, 805, 807, 810) so they are suspects but by his comments I would expect lower CP803/803 voltage. At caps CP802/803 I get 385 V when the BL is on and when it fails to light I get ~159V. At rest, TV off, the voltage is about 149V. BUDM calls for 390V but is 385V close enough?
Of note, when the BL fails to light, the voltage at CP802/803 drops to zero then jumps to ~350V then drops to ~159V. Under normal operation the Cap Voltage is resting between 385 & 149 and simply rises to 385 when the TV boots. I have obtained that data using a Fluke 77 and an older analog meter.
I have read about the JP852 jumper cutting and appreciate the wisdom expressed by BUDM of not cutting that component.
Since the TV works normally one can assume that both fuses on the board are not blown. I have checked though.
I should mention here that I’m not trained in electronics so I’m not in a place to do in depth analysis of the function of the board but I do have a rudimentary understanding of e.g. transistor basics. I’m confident of taking data and reasonably confident of component replacement (re-capped numerous assemblies) but shy on SMT experience. I do however have a hot air re-work station and several irons to choose from and given the choice of scrapping the TV, buying a new board or undertaking repairs, there’s little to lose by having a go at the board. I’m reasonably confident that I could replace the RP 802, 805, 807, 810 components if it came to that but close spaced 0603 might be a bit much.
As is customarily requested, I have taken data at the CN802 connector for normal and failed operation, that is below. Anomalies highlighted in bold:
Voltages on cable from PSU to mainboard, CN802
PIN ID - Normal - BL Failed
Pin 1 - B13v - 12.68 - 12.67
Pin 2 - 5vDet - 3.52 - 0.0
Pin 3 - B13v - 12.67 - 12.68
Pin 4 – BluOn - 5.06 - 5.05
Pin 5 - B13v - 12.67 - 12.68
Pin 6 – EPWM - 1.631 - 1.058
Pin 7 – Ground - 0.0 - 0.0
Pin 8 – Hsync - 1.67 - 1.665
Pin 9 – Ground - 0.0 - 0.0
Pin 10 – Ground - 0.0 - 0.0
Pin 11 - B5v - 5.10 - 5.10
Pin 12 – Ground - 0.0 - 0.0
Pin 13 - B5v - 5.10 - 5.10
Pin 14 - B5v - 5.10 - 5.10
Pin 15 - B13v - 12.66 - 12.68
Pin 16 - A5v - 5.13 - 5.13
Pin 17 - B13v - 12.66 - 12.68
Pin 18 – PSON - 0.877 - .862
VCaps CP802/803 - 385 -149.9
Oh, that's fussy, the forum software blew away the nice formatting I did on the table, LOL!
Notes and additional measurements:
Some have noted that Pin 18 PSON fluctuates between 2.5 & .72V, my voltage does NOT fluctuate.
Transformer T1802S White seems to squeal quietly as the TV boots, the squeal is shorter when the BL fails.
Voltage at VCC pin (18) of PFC ICP801 is 5.17 & Vin (Pin 1) is 11.03 when the BL is lit. No readings yet of when the BL fails, I did mention is sometimes and annoyingly fails to fail when you want it to…….
TOM66 asked a poster for the voltage across C1842, for me it is .599V when the BL fails. Tom66 said that would indicate a shutdown due to “under voltage lockout”. Would this be related to drifting of the (RP 802, 805, 807, 810) resistor chain BUDM has referenced? If so, the fix there seems obvious, replace the (RP 802, 805, 807, 810) resistor chain……. Does the resistance of that chain drift down or up with time? What about temperature? If that’s the case perhaps I can induce resistance change by altering temperature?
The last observations I have relate to the troubleshooting section of the Samsung (Service) training manual. To diagnose “No Power”, Samsung recommends checking voltage levels of several components, in my case none varied in voltage whether the BL failed or not. I read the check list to be looking for the case of a dead, no function unit although they do mention removing the 18p cable to force the BL on so there is an ambiguity. The checks they ask for are:
BD202
BD201
BD208
BD205
Pin3 of IC 207 (Seems to expect 3.3V), I have ~5.15 irrespective of BL status.
L201
L202
L204
L203
This checklist determines which PC Board to replace. I don’t think we learned anything from it.
Regarding my photos, they're ugly but it's a well known board so I chose to show my board vs re-posting things like shopjimmy images that show it clearly but are already here. Let me know if it's not good enough. I can also post the manuals I mentioned if they are useful to anyone.
So, where to from here?
Is the potential drift attributed to (RP 802, 805, 807, 810) resistor chain a realistic failure cause? Would the drift be higher or lower and would heating or cooling the chain provide useful information? What about the “under voltage lockout” suggested by Tom66? Is that related?
Given the intermittent nature of the BL fail, are any of the components "soft" such that they will go from working to not and return? I'm thinking of semiconductors more so than the resistor chain for example. Just a thought.
Any other areas to investigate? I’d hate to have to toss this thing out for want of a couple of components replaced. Cost, sustainability and all that!
Many thanks to those who have gone before me and to a couple of the very experienced and knowledgeable posters who have been following this from the beginning many years ago, your contributions are highly valued!
C152Heavy
Summary for TL-DR readers:
• Backlight is intermittent, may come on with TV boot or not. No flickering, never fails during TV on.
• Have obtained Samsung schematic & service documents - Can upload if helpful.
• Have read ALL applicable threads
• C1818 and CP820 replaced as low hanging fruit
• CN802 data taken for normal and failed BL operation. SUMMARY: Pin 2 - 5vDet = 3.52 @normal, 0.0 @BL fail. Pin 6 - EPWM = 1.631 @normal, 1.058 @BL fail.
• VCC pin (18) of PFC ICP801 is 5.17 & Vin (Pin 1) is 11.03 when the BL is lit, no failed data yet.
• VCaps CP802/803 = 385V @BL on, 149.9V @fail BL, ~159 @TV off
• Transformer “T1802S White” squeals during boot, shorter time when BL fails.
• Voltage across C1842 = .599V when the BL fails. Under voltage lockout?
The rest of the story:
To set a baseline, I have read all the BN44-00341B and LN46C630K1F threads, obtained the circuit diagram for BN44-00341B, obtained the Samsung Fast Track Troubleshooting Manual and Samsung (Service) Training Manual for the TV, the latter two from Elektrotanya BTW.
Symptoms: In normal use, the backlight may fail to come on when the TV is started. It can repeat for numerous re-starts, this is the detail of the problem I started with so I dug in and started to troubleshoot. The rest of the TV works (sound etc.).
On bench test sometimes the backlight will fail several times in a row then work. It can (only) sometimes be provoked to fail by unplugging while the TV is on and plugging back in. If the TV has been unplugged while on it starts up (boots) on its own when the plug is inserted.
On the bench it may not fail for many repeats of re-start which is maddening when you want to take some data while the backlight is failed!
I read about the C1818 and CP820 failures so even though they didn’t look failed I took an initial grab for low hanging fruit and replaced them, OK for a while but the BL failed to light again a few days later – basically back to the same symptoms proving that the caps were not failed. That led to a thorough reading of all the applicable threads and where I am today.
I have read BUDM’s comments about drift of the four 1.5M SMT resistor chain (RP 802, 805, 807, 810) so they are suspects but by his comments I would expect lower CP803/803 voltage. At caps CP802/803 I get 385 V when the BL is on and when it fails to light I get ~159V. At rest, TV off, the voltage is about 149V. BUDM calls for 390V but is 385V close enough?
Of note, when the BL fails to light, the voltage at CP802/803 drops to zero then jumps to ~350V then drops to ~159V. Under normal operation the Cap Voltage is resting between 385 & 149 and simply rises to 385 when the TV boots. I have obtained that data using a Fluke 77 and an older analog meter.
I have read about the JP852 jumper cutting and appreciate the wisdom expressed by BUDM of not cutting that component.
Since the TV works normally one can assume that both fuses on the board are not blown. I have checked though.
I should mention here that I’m not trained in electronics so I’m not in a place to do in depth analysis of the function of the board but I do have a rudimentary understanding of e.g. transistor basics. I’m confident of taking data and reasonably confident of component replacement (re-capped numerous assemblies) but shy on SMT experience. I do however have a hot air re-work station and several irons to choose from and given the choice of scrapping the TV, buying a new board or undertaking repairs, there’s little to lose by having a go at the board. I’m reasonably confident that I could replace the RP 802, 805, 807, 810 components if it came to that but close spaced 0603 might be a bit much.
As is customarily requested, I have taken data at the CN802 connector for normal and failed operation, that is below. Anomalies highlighted in bold:
Voltages on cable from PSU to mainboard, CN802
PIN ID - Normal - BL Failed
Pin 1 - B13v - 12.68 - 12.67
Pin 2 - 5vDet - 3.52 - 0.0
Pin 3 - B13v - 12.67 - 12.68
Pin 4 – BluOn - 5.06 - 5.05
Pin 5 - B13v - 12.67 - 12.68
Pin 6 – EPWM - 1.631 - 1.058
Pin 7 – Ground - 0.0 - 0.0
Pin 8 – Hsync - 1.67 - 1.665
Pin 9 – Ground - 0.0 - 0.0
Pin 10 – Ground - 0.0 - 0.0
Pin 11 - B5v - 5.10 - 5.10
Pin 12 – Ground - 0.0 - 0.0
Pin 13 - B5v - 5.10 - 5.10
Pin 14 - B5v - 5.10 - 5.10
Pin 15 - B13v - 12.66 - 12.68
Pin 16 - A5v - 5.13 - 5.13
Pin 17 - B13v - 12.66 - 12.68
Pin 18 – PSON - 0.877 - .862
VCaps CP802/803 - 385 -149.9
Oh, that's fussy, the forum software blew away the nice formatting I did on the table, LOL!
Notes and additional measurements:
Some have noted that Pin 18 PSON fluctuates between 2.5 & .72V, my voltage does NOT fluctuate.
Transformer T1802S White seems to squeal quietly as the TV boots, the squeal is shorter when the BL fails.
Voltage at VCC pin (18) of PFC ICP801 is 5.17 & Vin (Pin 1) is 11.03 when the BL is lit. No readings yet of when the BL fails, I did mention is sometimes and annoyingly fails to fail when you want it to…….
TOM66 asked a poster for the voltage across C1842, for me it is .599V when the BL fails. Tom66 said that would indicate a shutdown due to “under voltage lockout”. Would this be related to drifting of the (RP 802, 805, 807, 810) resistor chain BUDM has referenced? If so, the fix there seems obvious, replace the (RP 802, 805, 807, 810) resistor chain……. Does the resistance of that chain drift down or up with time? What about temperature? If that’s the case perhaps I can induce resistance change by altering temperature?
The last observations I have relate to the troubleshooting section of the Samsung (Service) training manual. To diagnose “No Power”, Samsung recommends checking voltage levels of several components, in my case none varied in voltage whether the BL failed or not. I read the check list to be looking for the case of a dead, no function unit although they do mention removing the 18p cable to force the BL on so there is an ambiguity. The checks they ask for are:
BD202
BD201
BD208
BD205
Pin3 of IC 207 (Seems to expect 3.3V), I have ~5.15 irrespective of BL status.
L201
L202
L204
L203
This checklist determines which PC Board to replace. I don’t think we learned anything from it.
Regarding my photos, they're ugly but it's a well known board so I chose to show my board vs re-posting things like shopjimmy images that show it clearly but are already here. Let me know if it's not good enough. I can also post the manuals I mentioned if they are useful to anyone.
So, where to from here?
Is the potential drift attributed to (RP 802, 805, 807, 810) resistor chain a realistic failure cause? Would the drift be higher or lower and would heating or cooling the chain provide useful information? What about the “under voltage lockout” suggested by Tom66? Is that related?
Given the intermittent nature of the BL fail, are any of the components "soft" such that they will go from working to not and return? I'm thinking of semiconductors more so than the resistor chain for example. Just a thought.
Any other areas to investigate? I’d hate to have to toss this thing out for want of a couple of components replaced. Cost, sustainability and all that!
Many thanks to those who have gone before me and to a couple of the very experienced and knowledgeable posters who have been following this from the beginning many years ago, your contributions are highly valued!
C152Heavy
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