Vizio SV422XVT no backlight, photos and details inside

[gustagen]

I had great luck with some kind souls who helped me troubleshoot and repair a ViewSonic LCD monitor last year. I'm hoping to find some more help with a Vizio TV whose backlight is not working.

Vizio SV422XVT backlight does not work at all. Audio and video work fine, and the picture is visible if a bright light is shone onto the screen.

Upon plugging the TV in, the power LED alternates from orange to white 90 times before going to steady orange. TV will not respond to the remote during this alternating blink. Power LED then turns steady orange, and when powered on the LED turns steady white.

I've removed the stand and rear panel and don't see any visually obvious faults. All connections seem secure. Caps all look unbloated and normal. When powered on, the LED on the topmost PCB (photo1) is steady blue for approximately 9 seconds, then dims to off.

Attached are photos of all three PCBs. Any ideas where to start troubleshooting? I have a multimeter and very limited knowledge of electronics. I can take other photos or closeups of certain areas if necessary. Thanks!

[JonathanAnon]

Re: Vizio SV422XVT no backlight, photos and details inside

Well it points to an inverter board fault, or possibly an issue with the power going to the inverter board. Do you know how to check the voltages going to from the power supply to the inverter board?

[gustagen]

Re: Vizio SV422XVT no backlight, photos and details inside

Thanks for your reply! I understand that the problem could be either with the inverter or with the voltage inputs to the inverter. I'm unsure where to test.

Am I correct in thinking that this TV has the power supply and inverter on the same PCB, the one in 'photo 2' in my original post? Any tips on where to measure for voltage and what readings to expect? Thanks again!

EDIT: After reviewing 'photo 2' again I see that there are instances of 5.1V, 12V, and 18V noted. Will I need to dismount the board to probe the underside?

[tom66]

Re: Vizio SV422XVT no backlight, photos and details inside

This TV uses high voltage inverter; driven from primary side. Can you list the pin legend next to the connectors on the PSU that go to the main board? There may be an ON/OFF or BL ON pin.

[MisterD]

Re: Vizio SV422XVT no backlight, photos and details inside

I had great luck with some kind souls who helped me troubleshoot and repair a ViewSonic LCD monitor last year. I'm hoping to find some more help with a Vizio TV whose backlight is not working.

Vizio SV422XVT backlight does not work at all. Audio and video work fine, and the picture is visible if a bright light is shone onto the screen.

Upon plugging the TV in, the power LED alternates from orange to white 90 times before going to steady orange. TV will not respond to the remote during this alternating blink. Power LED then turns steady orange, and when powered on the LED turns steady white.

I've removed the stand and rear panel and don't see any visually obvious faults. All connections seem secure. Caps all look unbloated and normal. When powered on, the LED on the topmost PCB (photo1) is steady blue for approximately 9 seconds, then dims to off.

Attached are photos of all three PCBs. Any ideas where to start troubleshooting? I have a multimeter and very limited knowledge of electronics. I can take other photos or closeups of certain areas if necessary. Thanks!

As for Vizio Logo alternating from orange to white 90 times, I have a 42" Vizio that always does that if I happen to unplug it and plug back in, the amount times it alternates or blinks seems to vary depending on how long it's left unplugged, mine works with no problems at all, so I would say that part is normal and is most likely the standby circuit capacitors discharging.

[gustagen]

Re: Vizio SV422XVT no backlight, photos and details inside

I've attached a photo of the three connectors from the PSU to the main board. I tested all pins with the TV powered ON.

Connector CN202 has four pins, two 18V and two grounds. These tested good.

Connector CN203 has three pins. Here are their labels and the readings I got:

DIM 1: 2.9 V
DIM 2: 2.9 V
INV_ON/OFF: 3.3 V

Connector CN201 has 16 pins. The ones with marked voltages tested good, as did the grounds. Two pins were not labeled with voltages, here are the readings I got:

STANDBY: 3.3 V
N.C: 2.1 millivolts

Thanks so much for all your input everyone!

EDIT: I should mention that I did all testing with the cables connected. I detached them for the photo.

[tom66]

Re: Vizio SV422XVT no backlight, photos and details inside

OK, so INV ON/OFF is HIGH, backlight should be on but it is not.

There are two fuses of interest on the board. F501 and F601. Can you test them? They're next to the two largest "K" Rubycon capacitors.

[budm]

Re: Vizio SV422XVT no backlight, photos and details inside

Can we see good clear pictures of the bottom side of the power supply/inverter board as a whole and also four 1/4 section so I can trace out the connections?

[gustagen]

Re: Vizio SV422XVT no backlight, photos and details inside

OK, I've tested fuses F501 and F601. Both are good. The fuse next to the 3-prong 120V input is also good.

Attached are four photos of the back of the PSU / inverter PCB. One is of the entire board, the others are the board split into thirds with some overlap.

[retiredcaps]

Re: Vizio SV422XVT no backlight, photos and details inside

Can we see good clear pictures of the bottom side of the power supply/inverter board as a whole and also four 1/4 section so I can trace out the connections?

@gustagen, what budm is going to do takes a lot of his time to trace out and draw you a schematic. If you are not going to follow through on this repair, say so now so he doesn't waste potentially hours of his time.

Thank you.

PS. Those are excellent clear focused photos.

[budm]

Re: Vizio SV422XVT no backlight, photos and details inside

OK, can you tell me the DC voltage reading on the large cap C909/C910? The negative legs of these two caps is the Ground ref point for the primary side. Also check and see the voltage reading of the fuse F501 which feeds the B+ for the backlighs inverter circuits.

[gustagen]

Re: Vizio SV422XVT no backlight, photos and details inside

@retiredcaps: Thanks for the heads-up, and I appreciate your concern for your fellow forum-goer! I'm certainly following through with this repair.

@budm: Let me make sure what you're asking me to do. I will reconnect all connections to the PSU/inverter board and power the TV on, then measure voltage across the legs of the caps. Since I'll need access to the rear of the board, will a lead with alligator clips between the chassis and a screw hole on the PCB provide sufficient ground to the board?

EDIT: I see you've edited your post to clarify. I will report back with cap voltages and for fuse F501.

[retiredcaps]

Re: Vizio SV422XVT no backlight, photos and details inside

@retiredcaps: Thanks for the heads-up, and I appreciate your concern for your fellow forum-goer! I'm certainly following through with this repair.

I'm glad you didn't take my post the wrong way.

Lately, we have had some 100+ posts/thread where the OP went AWOL or gave up and it leaves many of the regulars frustrated to see their hours of work and help go down the drain without even a thank you.

PS. Did you replace the caps on the Vizio? It is unusual to see Rubycon caps on a Vizio?

[budm]

Re: Vizio SV422XVT no backlight, photos and details inside

When you are measuring the voltage in the Primary side of the circuits where the C909/910 are, you WILL NOT be using the chassis as the ground ref point, chassis is the ground ref point for the COLD side of the circuits. So you will be using the Negative leg of either C909 or C910 (these two caps are connected in parallel) as the ground ref which where the black probe of you meter will be. See the picture where you can connect the black probe to which you may be able to get to on the top side of the board on one of the jumper. I also need P/N of the components so I can look up the spec sheets.

[budm]

Re: Vizio SV422XVT no backlight, photos and details inside

This board is not very expensive, http://www.shopjimmy.com/vizio-0500-...t-inverter.htm

[gustagen]

Re: Vizio SV422XVT no backlight, photos and details inside

@retiredcaps: I can understand everyone's frustration with those who don't follow up on free advice! This Vizio belongs to a friend, but has not been serviced as far as I know. It was about 18 months old when this problem arose.

@budm: I've measured the voltage across C909 and C910. Both read 392V. I used the negative legs as my ground reference for all measurements during this test session.

Voltage between the caps' negative leads and both ends of F501 measures 392V.

The eight transistors you've circled all seem to have the same part numbers. They are all very difficult to read because they seem not to have been stamped hard enough for all digits to be clear, and are coated with a shiny, gummy substance. Using a magnifying glass and piecing the part numbers together from each one, I'm confident they say:

1K32CB
DD
5N50

The two IC's also seem identical. They seem to read:

OZ9966GN
A94QRJIT
0926B2

I also want to mention that I am confused about the location/existence of F601. You suggested earlier that I test it along with F501 and I reported them as both good. However, the text "F601" on the front side of the PCB is right next to a small, white, rectangular component that has "ICP250 4A00SMT" printed on it. Googling has led me to believe this is a resistor, not a fuse. Its leads are bounded by a box printed on the rear of the PCB and marked GR3. The F601 mark on the front of the PCB doesn't seem to correspond to any component. Also, what does FB602 refer to on the rear of the PCB, just to the right of the caps we've been discussing?

I had priced the entire PSU/inverter PCB as well. Are you confident that replacing it would solve the problem? What are the chances of the same issue occurring with the new board as well? I would love to solve the problem by replacing a component or two, and I'm hesitant to throw $50 at it without assuring my friend that the issue will be resolved.

Thanks again to everyone for the help!

[budm]

Re: Vizio SV422XVT no backlight, photos and details inside

The White rectangular box (F501) is the fusible resistor which feeds the B+ to those 8 MOSFET, if it is open, then the inverter will not work, that is why when you measure each end with ref to primary ground, it should have 382VDC on it. The 382VDC is what I expect, it is telling me that the PFC Voltage booster circuits are working OK. The F601 looks like it belongs to the white cylinder fuse.

[gustagen]

Re: Vizio SV422XVT no backlight, photos and details inside

I think you may have transposed F501 and F601 in your last post. Please correct me if I'm wrong, but I think F501 is the white cylindrical fuse with the yellow stripe and F601 is the rectangular box you referred to as a fusible resistor.

I neglected to mention that during my last test I measured for voltage between the negative leg of C909/C910 and each leg inside the box marked GR3. I got 392V at the leg on the caps' side of the box, and 0V on the other leg. See attached photo for clarification.

Does this indicate a faulty fusible resistor? I apologize if I'm over-complicating these simple tests, I just want to be sure I'm giving you accurate test results.

[selldoor]

Re: Vizio SV422XVT no backlight, photos and details inside

Budm has transposed the F601 and F501 as you surmise. In the box GR3 are the
solder points for the Fusible resistor F601 and you should have the 392vdc voltage on both pins.
So, yes it is faulty. Try a resistance test on it or remove from circuit and test.
FB 602 is a ferrite bead - they do not often fail a simple continuity test should show if
it is faulty.

[gustagen]

Re: Vizio SV422XVT no backlight, photos and details inside

I will measure the resistance of F601. Should this be done while powered on? Will removing it from the board give a more accurate reading?

In the meantime, I'm having difficulty finding a replacement online. Searching on "ICP250 4A00SMT" yielded no results. I have found similar looking components by doing a Google Image search on "fusible resistor." Is it possible that I am not using the proper terminology or part number format to find it? Are the markings on the part a list of specs rather than an actual part number?

I had measured for continuity through FB602 in an earlier test and found it was present.