Hi everyone,
I am currently in the process of diagnosing and (hopefully) repairing my 37 in Vizio, and could really use some help.
Background:
My friend's Vizio VW37 recently broke (I think it is a few years old), and he told me I could have it. I had already fixed one LCD before (my sisters Samsung, with obviously bad bloated capacitors on the power supply), and was/am feeling confident that I can fix this issue without needing to buy new boards (i.e. a fix done by replacing individual caps/chips instead of just the entire board). I like to think my skill level is decent: I am finishing up my undergrad EE career and plan on getting my masters, I have a well stocked workspace (Weller soldering iron, a shiny new Fluke 115 I just got for my birthday, third hands, hemostats, etc), and I have been soldering and de-soldering various electronics for close to 10 years.
The Problem:
When the TV is plugged in the Vizio logo glows orange. An attempt to turn the TV on (using either the power button or the remote - both "work") will result in a few second delay before the Vizio logo turns white but nothing else happens (no sound, image, etc). A bright light was held up to the screen to see if the pixels were actually changing, in case it was strictly a bad back-light , but no pixels were seen to change. The logo remains white and the TV can be "shut off " normally using the remote or the power button.
My Diagnostics and Fix Attempt:
The first thing I did after I took the back of the TV off was to look for obviously bloated/damaged capacitors, but none were readily apparent. I then used my multimeter to test the voltages the power supply board was giving off. The connector to the main board was correctly giving off 5v at 3 of the pins, but the 12v pins were reading 0v. The 24v pins going to the inverter board were also giving off 0v.
I de-soldered a large heat-sink for the the power transistors on the secondary side of the power board in order to get a better look at the capacitors underneath it. The capacitors feeding the 12v and 24v pins were bulging very slightly (it seemed, now I think it was probably just in my imagination).
Pics:
Above: The two slightly bloated 36v 680 micro-farad capacitors feeding the 24v pins going to the inverter board (the two 16v caps feeding the 12v pins were in the process of being replaced when this photo was taken).
Above: A closeup of the slightly bloated 36v caps (the two new 16v caps can be seen in the background)
"Great" I thought - this plus the incorrect voltage readings made me think I had found the problem, so I jumped on e-bay and ordered some new caps for a few bucks. When the 16v 1500 micro-farad caps that feed the 12v pins arrived, I de-soldered the old ones and put in the new ones (which can be seen in the second photograph just above the caps with the red arrows). I plugged in the power cord and tested the voltage off the 12v pins, damn - still 0v.
To the INTERNET!
My searching brought me to a few various forums. I read through many of them, including the problems and fixes from this badcaps post:
https://www.badcaps.net/forum/showthread.php?t=13615
along with the numerous other links that thread went to, and the fix attempts on those threads. There was a lot of good info, and I learned much about how a SMPS works, but still nothing that was able to fix my particular problem.
After reading through a number of different threads, I felt like I was closing in on the problem. One thing I read, which I briefly thought may be the problem, was that the power board needed to be connected to the main board, and receive a Power Supply On (PSON) signal before it output anything on the higher voltage pins.
:
:
I was testing the voltage on the pins while the board was still sitting on my desk disconnected from everything but the mains. I quickly realized why having a PSON made perfect sense. When the TV is in standby mode, it does not require electricity - except for the 5v to the main board to power the IR receiver and various components that will tell the TV when to fully power on. There is no need to have 24v going to the inverter, or 12v going to the main board (which I am guessing powers the speakers).
I screwed the power supply board back into the metal frame, and made all the necessary wire connections, and connected my multimeter to one of the 12v pins. I then powered up the TV with the remote, waited for the logo to turn white, and then checked the voltage - still 0v. The PSON pin did jump from .014v to 3.166v when the TV was "turned on", so at least the mainboard was correctly responding to the power-on input signal from the remote.
I have also checked all the diodes I could identify, and they all seem to be in working order. There is no voltage at the output of either the 12v or 24v power transistors (or the transformer) on the low voltage side of the board (tested with the PSON pin being off and HIGH at 3.166v, so I guess I wasted a few bucks on electrolytic capacitors - no great loss).
Here are some shots of the front and back of the power supply with labels added:
Front:
Back:
There seemed to be heat "damage" to the mechanical solder connection that held on the heatsink that was attached to IC901. It looked like this chip got the heatsink hot enough to melt the solder. A picture of this is shown below:
The ceramic capacitor that is next to this heatsink is also chipped on the top, shown below:
There were other signs of solder being reheated. Shown below is a solder joint for a jumper wire. This jumper wire connects the source of the 20N60C3 power transistor to a group of 4 resistors wired in parallel (R825 A,B,C, and D).
One other spot where it looked like the solder had gotten hot was at the SCK 2512 Thermistor, shown in the picture below. The joint which had gotten hot was connected directly the neutral line of the power cord.
One other small portion that looked like it may have been heat damaged was a diode that is located on the HV side very close to the opto-couplers. A picture of this is shown below.
I am not sure if these photos of apparent heating, are actually damage or just results of normal board use, or possibly results of overheating without the components actually being damaged.
I decided to attack the problem from the HV side for a bit. The large 450v 150micro-farad capacitor that filters the output from the full-wave input rectifier was measuring 169.7-170 volts, so everything was good up until that point.
One interesting thing I noticed was that all the heat-sinks on the high voltage side were reading -62.6 VDC when compared to the mains/chassis ground. I measured the high voltage side of two of the opto-couplers, and this -62.6 VDC also appeared.
So this is where I am at now. If anyone has any advice, it would be greatly appreciated.
TL;DR
Power supply not turning on the 12v & 24v outputs, even though a PSON signal of 3.166 is being sent to the HV side.
I am currently in the process of diagnosing and (hopefully) repairing my 37 in Vizio, and could really use some help.
Background:
My friend's Vizio VW37 recently broke (I think it is a few years old), and he told me I could have it. I had already fixed one LCD before (my sisters Samsung, with obviously bad bloated capacitors on the power supply), and was/am feeling confident that I can fix this issue without needing to buy new boards (i.e. a fix done by replacing individual caps/chips instead of just the entire board). I like to think my skill level is decent: I am finishing up my undergrad EE career and plan on getting my masters, I have a well stocked workspace (Weller soldering iron, a shiny new Fluke 115 I just got for my birthday, third hands, hemostats, etc), and I have been soldering and de-soldering various electronics for close to 10 years.
The Problem:
When the TV is plugged in the Vizio logo glows orange. An attempt to turn the TV on (using either the power button or the remote - both "work") will result in a few second delay before the Vizio logo turns white but nothing else happens (no sound, image, etc). A bright light was held up to the screen to see if the pixels were actually changing, in case it was strictly a bad back-light , but no pixels were seen to change. The logo remains white and the TV can be "shut off " normally using the remote or the power button.
My Diagnostics and Fix Attempt:
The first thing I did after I took the back of the TV off was to look for obviously bloated/damaged capacitors, but none were readily apparent. I then used my multimeter to test the voltages the power supply board was giving off. The connector to the main board was correctly giving off 5v at 3 of the pins, but the 12v pins were reading 0v. The 24v pins going to the inverter board were also giving off 0v.
I de-soldered a large heat-sink for the the power transistors on the secondary side of the power board in order to get a better look at the capacitors underneath it. The capacitors feeding the 12v and 24v pins were bulging very slightly (it seemed, now I think it was probably just in my imagination).
Pics:
Above: The two slightly bloated 36v 680 micro-farad capacitors feeding the 24v pins going to the inverter board (the two 16v caps feeding the 12v pins were in the process of being replaced when this photo was taken).
Above: A closeup of the slightly bloated 36v caps (the two new 16v caps can be seen in the background)
"Great" I thought - this plus the incorrect voltage readings made me think I had found the problem, so I jumped on e-bay and ordered some new caps for a few bucks. When the 16v 1500 micro-farad caps that feed the 12v pins arrived, I de-soldered the old ones and put in the new ones (which can be seen in the second photograph just above the caps with the red arrows). I plugged in the power cord and tested the voltage off the 12v pins, damn - still 0v.
To the INTERNET!
My searching brought me to a few various forums. I read through many of them, including the problems and fixes from this badcaps post:
https://www.badcaps.net/forum/showthread.php?t=13615
along with the numerous other links that thread went to, and the fix attempts on those threads. There was a lot of good info, and I learned much about how a SMPS works, but still nothing that was able to fix my particular problem.
After reading through a number of different threads, I felt like I was closing in on the problem. One thing I read, which I briefly thought may be the problem, was that the power board needed to be connected to the main board, and receive a Power Supply On (PSON) signal before it output anything on the higher voltage pins.
:
:I was testing the voltage on the pins while the board was still sitting on my desk disconnected from everything but the mains. I quickly realized why having a PSON made perfect sense. When the TV is in standby mode, it does not require electricity - except for the 5v to the main board to power the IR receiver and various components that will tell the TV when to fully power on. There is no need to have 24v going to the inverter, or 12v going to the main board (which I am guessing powers the speakers).
I screwed the power supply board back into the metal frame, and made all the necessary wire connections, and connected my multimeter to one of the 12v pins. I then powered up the TV with the remote, waited for the logo to turn white, and then checked the voltage - still 0v. The PSON pin did jump from .014v to 3.166v when the TV was "turned on", so at least the mainboard was correctly responding to the power-on input signal from the remote.
I have also checked all the diodes I could identify, and they all seem to be in working order. There is no voltage at the output of either the 12v or 24v power transistors (or the transformer) on the low voltage side of the board (tested with the PSON pin being off and HIGH at 3.166v, so I guess I wasted a few bucks on electrolytic capacitors - no great loss).
Here are some shots of the front and back of the power supply with labels added:
Front:
Back:
There seemed to be heat "damage" to the mechanical solder connection that held on the heatsink that was attached to IC901. It looked like this chip got the heatsink hot enough to melt the solder. A picture of this is shown below:
The ceramic capacitor that is next to this heatsink is also chipped on the top, shown below:
There were other signs of solder being reheated. Shown below is a solder joint for a jumper wire. This jumper wire connects the source of the 20N60C3 power transistor to a group of 4 resistors wired in parallel (R825 A,B,C, and D).
One other spot where it looked like the solder had gotten hot was at the SCK 2512 Thermistor, shown in the picture below. The joint which had gotten hot was connected directly the neutral line of the power cord.
One other small portion that looked like it may have been heat damaged was a diode that is located on the HV side very close to the opto-couplers. A picture of this is shown below.
I am not sure if these photos of apparent heating, are actually damage or just results of normal board use, or possibly results of overheating without the components actually being damaged.
I decided to attack the problem from the HV side for a bit. The large 450v 150micro-farad capacitor that filters the output from the full-wave input rectifier was measuring 169.7-170 volts, so everything was good up until that point.
One interesting thing I noticed was that all the heat-sinks on the high voltage side were reading -62.6 VDC when compared to the mains/chassis ground. I measured the high voltage side of two of the opto-couplers, and this -62.6 VDC also appeared.
So this is where I am at now. If anyone has any advice, it would be greatly appreciated.
TL;DR
Power supply not turning on the 12v & 24v outputs, even though a PSON signal of 3.166 is being sent to the HV side.
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