View Full Version : More lightning damage


rlovison
08-12-2014, 04:24 PM
I have a Sony Bravia LCD KDL-46BX420 that was also a victim of a lightning strike. When I plug this set in, I get two distinct clicks and then nothing. The voltages are in the tenths of volts or 0 at the output leading to the main board. If I unplug and plug in again I won't get any clicks from the relay unless I wait a few minutes before plugging in. All the diodes check out ok on the power supply board, fuse is ok along with the resistors (none were open). Not sure where to start with this one. Does anyone have any pointers on where to begin? Thanks.

andy
08-12-2014, 07:00 PM
Lightning can go almost anywhere. If it got past the power supply, it's probably scrap. Even with 80's and 90's CRTs, I saw a lot of sets that were beyond repair due to lightning.

I would start at the line input and trace forward from there. Does the power supply have any output if you keep it unplugged from the main board?

rlovison
08-12-2014, 07:52 PM
I would start at the line input and trace forward from there. Does the power supply have any output if you keep it unplugged from the main board?

Hi Andy. Thanks for offering help.

Here are the readings at the output of the power supply leading to the main board with the main board unplugged:

standby - 3.29V
acoffdet - 3.29V
power on - 0V
Au12V - 0V
Au12Vgnd - 0V
Reg12Vgnd - 0v
Reg12Vgnd - 0v
Reg12V - 0V
Reg12V - 0V
BL-ERR - .397V
BL-ON - 0V
D1 - 0V
ACT-STBY - 0V
T-Con-12V - 0V
T-Con On - 0V

http://videokarma.org/attachment.php?attachmentid=183948&d=1407888992

rca2000
08-13-2014, 02:07 AM
This means that the standby supply is at least working to a degree. It may not be just right...but it IS working.

NOW--what you need to look for it: are you getting a "power on" command to the PS board, from the signal board ?? This will appear ONLY when you press the power button, on the set or remote. It should NOT be there when the set is off.

Hook up the PS board, and monitor the power on line. If it is at 3V. or so before you hit the power button, see if it "changes' to a low, near 0. If it is already 0, see if it goes to about 3 volts. One way or another it MUST see a BIG change--in order to turn the "run supply" on.

If you get the PS on command--and do NOT see the other voltages at some other pins, such as maybe 12 volts, and such..THEN it means that the run portion of the power supply has taken a hit. I would suspect those FETS's on that sink, down the middle of the board are shorted and that white fuse resistor near them is then open. ALSO--if this is the case--I think there will be a chip near the middle of the board on the other side--that is the SMPS controller. It may also be bad.

IF...you are getting a good on command--then at least a PART Of your signal board is good. I worked on a set like this recently. It had a dead standby chip (that little one on the right side of the board with the weird pin-out.) .AND a dead-shorted BL inverter board. After I got the standby supply running..I THOUGHT I had a bad signal board, since nothing would come on. BUT...I found that my on command was fine from the signal board, and when I unplugged that cable from the BL inverter--the set would try to come on--even make a "chime" in the speakers--but with no BL--it shut down. I was able to get a good inverter board for a very low price--and saved the repair for the customer. SO...If you get a good on command...unplug that cable to the BL inverter...(on the OTHER side of the PS the one NOT gong to the signal board) and try again. if the set then tries to come on...you likely have a shorted inverter. Mine had a dead short on the 24 volt line--severly loading the run supply and causing shutdown.

But..IF you have a good 3 volt line and NO change in the power on command...and after you unplug ALL other possible problems, (such as the panel and T-con) , you may INDEED have a bad signal board.. But try what I said first. You may just have a dead Power supply, and it might can be foxed--or perhaps ordrerd on ebay.

rlovison
08-13-2014, 08:37 AM
This means that the standby supply is at least working to a degree. It may not be just right...but it IS working.

NOW--what you need to look for it: are you getting a "power on" command to the PS board, from the signal board ?? This will appear ONLY when you press the power button, on the set or remote. It should NOT be there when the set is off.

Hook up the PS board, and monitor the power on line. If it is at 3V. or so before you hit the power button, see if it "changes' to a low, near 0. If it is already 0, see if it goes to about 3 volts. One way or another it MUST see a BIG change--in order to turn the "run supply" on.

When I plug the set in, I get two clicks. I don't get a lit standby led and the power on/off switch does nothing. If I monitor the poweron pin on the output of the power supply when I plug the unit in, I initially get a small voltage reading of around a volt but then drops to zero.

The white fuse resistor is OK as well as any of the other fuses and resistors on the board.

Something I just tried... if I connect a 3 volt power supply up to the poweron pin, the relay clicks twice without any ac going to the power supply. It does this three of four times with 10 seconds or so in between the double clicks before the relay stops clicking all together.

dr.ido
08-13-2014, 09:10 AM
When you use the external power supply it likely tries to start, but then clicks off when it doesn't see the voltages it expects to come up.

Another way to test the power supply is to jumper the power on pin to the standby 3.3V (ideally with a 100 ohm or so resistor). This should cause at least one of the 12V rails to come up.

While it's probably not related to your problem I've noticed on some Bravias that the standby LED does not light when power is first applied. When the is switched on with either the front panel button or remote it will light green. If it is switched off with front panel button it will go off. If it is switched off with the remote it will light red. If it is flashing red the number of flashes is the fault code.

rlovison
08-13-2014, 09:27 AM
OK, more tests. I disconnected the main board and inverter board from the power supply. I hooked up a 3V power supply to the poweron pin. When I plug the set in, I get one relay click. I get 12V at the "Reg12V" pins leading to the main board and 25V at pins leading to the inverter board. I get 0V at the "T-Con-12V" pin leading to the main board... not sure if this should be normal since the main board is disconnected.

Thanks for the info on the power led.

It seems to me the problem is pointing to the main board and the power supply board might be OK. Does this seem correct?

andy
08-13-2014, 12:02 PM
You may need to apply power to the T-Con On pin to activate the T-Con-12V. I would try forcing the power on while it's connected to the main board.

As a quick check of the main board, you can look for 3.3v going to the main micro controller. If it is, and you have an oscilloscope, see if the clock crystal for the micro is running.

If there's no 3.3v at the micro, then you need to trace the power pins on the micro to their source. Sometimes a bad micro, or other failed parts will pull down the standby supply. If you're lucky, there might be an open fuse hidden somewhere.

rlovison
08-13-2014, 06:58 PM
As a quick check of the main board, you can look for 3.3v going to the main micro controller. If it is, and you have an oscilloscope, see if the clock crystal for the micro is running.

If there's no 3.3v at the micro, then you need to trace the power pins on the micro to their source. Sometimes a bad micro, or other failed parts will pull down the standby supply. If you're lucky, there might be an open fuse hidden somewhere.

Thanks for the tips.

In the Sony's current condition, I'm not able to perform these tests. With the main board plugged into the power supply, within seconds after plugging the unit in, the standby voltage drops to .5V. This only happens with the main board plugged in otherwise, it's at 3.29V. Lightning does strange things to electronics. :)

andy
08-13-2014, 09:16 PM
Thanks for the tips.

In the Sony's current condition, I'm not able to perform these tests. With the main board plugged into the power supply, within seconds after plugging the unit in, the standby voltage drops to .5V. This only happens with the main board plugged in otherwise, it's at 3.29V. Lightning does strange things to electronics. :)

I forgot about that. Then something on the main board must be pulling down the standby supply. It could be as simple as a shorted diode, or beyond repair. As a last resort, you could connect an external (ideally variable current) power supply to the standby input to the main board. What ever is pulling too much power will probably get hot and be easy to find.

dr.ido
08-14-2014, 10:00 AM
At this point I'd say the power supply is fine. I'd check any regulators on the main board and anything else obvious, but beyond that replacing the main board is probably the only option.

rlovison
08-15-2014, 05:27 PM
Just ordered one. I'll update sometime next week. Thanks for the help and advice..

rlovison
08-19-2014, 09:35 PM
The main board was the problem. All is well... beautiful picture. Thanks to all that helped.