I am currently on a troubleshoot of 46” Sony KDL-46BX450 tv. I came back from Washington to Texas on medical emergency and had to leave all my tools up there. All I have is a couple of screwdrivers and a dvm. I wish to ask the community a troubleshooting question. Please forgive stupid questions as meds I am taking produce brain fog.
I have well maintained Sony KDL-46BX450. It went black one day. After turn-on, I get solid green light and Sony logo in screen center for about 1-2 seconds, then black. No blinking LEDs, no hissing. Flashlight test shows screen characters dimly viewable, so tv is probably ok, just no backlight. After taking apart, I measured voltages on the Samsung SS1460_12F01 inverter board connector CN6401, with power on, which matched what others had reported for this board. They were:
Stby: 3.3v
AC Off: 3.04v
Power On: 3.29v
Audio 12: 12.6v
Audio 12: 12.6v
Audio Gnd: 0v
Audio Gnd: 0v
Reg. 12v: 12.6v
Reg. 12v: 12.6v
BL-EER: 1.64v
BL On: 3.12v
TCon Vcc12: 12.56v
TCon On: 3.31v
I pulled the inverter board up and gave it a close inspection, no hot spots revealed, solder looked in good condition. Careful inspection of caps revealed all in good condition, Rubycon type caps. Board looks like it has six transformers to drive the ccfl tubes (three dual transformers top, center and bottom pn# 340158AD). Measurement of each of six transformer secondaries in ohms is from top to bottom:
1. 1297
2. 1367
3. 1389
4. 1393
5. 1388
6. 1391
Although topmost transformer 1 is 6.89% lower than the highest #4, it is not burn-up. Maybe has shorted across several windings enough to lower the resistance a little.
Obviously, the easy troubleshoot is substitution with good board. If still bad, then ccfls likely bad. However, I don't have that luxury. I know these transformers and or inverter boards are pretty much impossible to find this side of China. So I had an idea.
As I understand, reading from many badcaps posts, bad backlight could be bad inverter board or bad ccfl, Any single failure with inverter transformer or single ccfl will shut down the entire backlight within a second or two. I think this explains the Sony logo visible for the first few seconds in screen center.
I assume that the ccfls are arranged in six strips across the set running horizontally from top to bottom each driven from one of the six transformers. I assume that if I can see the Sony logo in the center before the backlight board shuts down, then the center transformer and center ccfl set must be ok. If that is a valid assumption, then could I swap the transformer in question (top of set) with the assumed good one (center of set) and see if the Sony logo is visible before shutdown again. If it is not, then that is a bad transformer, if it is visible, then likely the top ccfl is bad. Is this reasonable or faulty logic? Is there a better way to isolate the fault without additional components or tools beyond a DVM?
I have well maintained Sony KDL-46BX450. It went black one day. After turn-on, I get solid green light and Sony logo in screen center for about 1-2 seconds, then black. No blinking LEDs, no hissing. Flashlight test shows screen characters dimly viewable, so tv is probably ok, just no backlight. After taking apart, I measured voltages on the Samsung SS1460_12F01 inverter board connector CN6401, with power on, which matched what others had reported for this board. They were:
Stby: 3.3v
AC Off: 3.04v
Power On: 3.29v
Audio 12: 12.6v
Audio 12: 12.6v
Audio Gnd: 0v
Audio Gnd: 0v
Reg. 12v: 12.6v
Reg. 12v: 12.6v
BL-EER: 1.64v
BL On: 3.12v
TCon Vcc12: 12.56v
TCon On: 3.31v
I pulled the inverter board up and gave it a close inspection, no hot spots revealed, solder looked in good condition. Careful inspection of caps revealed all in good condition, Rubycon type caps. Board looks like it has six transformers to drive the ccfl tubes (three dual transformers top, center and bottom pn# 340158AD). Measurement of each of six transformer secondaries in ohms is from top to bottom:
1. 1297
2. 1367
3. 1389
4. 1393
5. 1388
6. 1391
Although topmost transformer 1 is 6.89% lower than the highest #4, it is not burn-up. Maybe has shorted across several windings enough to lower the resistance a little.
Obviously, the easy troubleshoot is substitution with good board. If still bad, then ccfls likely bad. However, I don't have that luxury. I know these transformers and or inverter boards are pretty much impossible to find this side of China. So I had an idea.
As I understand, reading from many badcaps posts, bad backlight could be bad inverter board or bad ccfl, Any single failure with inverter transformer or single ccfl will shut down the entire backlight within a second or two. I think this explains the Sony logo visible for the first few seconds in screen center.
I assume that the ccfls are arranged in six strips across the set running horizontally from top to bottom each driven from one of the six transformers. I assume that if I can see the Sony logo in the center before the backlight board shuts down, then the center transformer and center ccfl set must be ok. If that is a valid assumption, then could I swap the transformer in question (top of set) with the assumed good one (center of set) and see if the Sony logo is visible before shutdown again. If it is not, then that is a bad transformer, if it is visible, then likely the top ccfl is bad. Is this reasonable or faulty logic? Is there a better way to isolate the fault without additional components or tools beyond a DVM?
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