VIZIO VO42L No picture, No Sound

[Freezer]

Re: VIZIO VO42L No picture, No Sound

My latest project is a Vizio VO42LFHDTV10A 42" television. The person I got the TV from said the screen went black but the audio still worked. My first test was the old flashlight into the screen test. I was able to see the image, so I know the problem has something to do with the backlights.

After opening the TV I was surprised by how simple everything looked. I mean I've seen monitors half the size of this TV that have more boards and cables in them. In the middle is the power board, below that is the main video board, and on the left and right are the two inverter boards (sorry I didn't get an overall picture of the TV layout).

From the power board to the inverter boards is a single bundle of wires. According to the silk-screening on the power board the wires were ground, standby, power (either 12V or 24V, I forget which), and 'A' and 'B'. My guess is 'A' and 'B' carry voltage to tell the inverter boards to turn on. First I probed all the wires with the TV in standby. All pins read 0 except 4.9V on the standby lines - so that's as expected. Next I probed the pins with power on. Still 4.9 on the standby, either 12 or 24 on the power lines (again, I forget which), and 'A' and 'B' have 5V and 3.3V. So the voltages coming from the power board appear to be good.

Next I removed the inverter boards for a closer look. When viewing the monitor from the rear, the master board is on the left and the slave board is on the right. The surface mount fuses are good, and the ESR on the caps checks out. Also, the resistance between the different windings of the inverters is consistent, so I'm guessing the inverters are fine. As posted by Dgtech here I checked the mosfets and driver IC. All 4 mosfets on the master board check out. But one of the 4 mosfets on the slave board has a very low reading. So either the mosfet is bad, or the driver IC. Looking more closely at the driver IC I can see the problem. There is a small brown spot and very slight bulge on top of the chip right at pin 26. What's more, pin 26 is gone. I'm guessing the chip literally blew creating the brown spot and ejected the pin from the IC. I've included a close up picture of the bad chip.

So by now I'm convinced the problem that driver IC (BD9897FS). I ended up ordering a new one from the only place I could fine it... eBay. It cost $5.90 including shipping from a distributor in China. The chip arrived in less than 1 week from China (much quicker than I was expecting).

Now the matter of desoldering the old and soldering in the new. I have never done any SMD work, but I do have a nice solder station (Hakko 936) with a small tip. I decided to use ChipQuik SMD Removal Solder as demo'ed in this video. That ChipQuik stuff works great! The chip was off in about 10 seconds. After that a little solder wick the clean up the pads and I was ready to solder in the new chip.

As it turns out, soldering in the replacement was a lot trickier than I was expecting. It took a while to get the chip properly aligned. While soldering I created 2 solder bridges which took a while to clear using solder wick. Once I was finally done I took two close up pictures (see below) of the chip to verify my soldering. By no means a professional job, but considering this is my first ever attempt at SMD soldering I felt it went pretty good. Also, I took a picture of the old chip on top of a dime to give you some perspective of the size.

After all the soldering I put the board back in and the TV works like a charm. I'm going to run the TV for a while to make sure the repair holds, but it looks like for $5.90 in repair parts I have a 42" TV.

Many thanks to the members of this forum. All the knowledge I've gained reading your posts made this possible. And a special thanks to Dgtech for his post!

[Dgtech]

Re: VIZIO VO42L No picture, No Sound

This forum helped me get started as well. So we all, yourself included, contribute to it's overall kick-ass wealth of knowledge.

I dont know if I had posted this before but because of this engineering flaw, Philips reccomends backing off of the brightness and contrast. I personally had tested this theory before. I had the brightness and contrast up and the set made a hum (with volume muted). I then could hear the plastic contracting as it heated up. I could smell the transformers getting heat. I now keep brightness at about 75 and contrast at about 75. These settings are just below the hum. I'm sure that will extend the life greater.

These inverters are in a great number of sets and will be a cause of failure all over the place. After my 2nd repair of replacing the chip, I bought a set of 10 of them, knowing I would see it again. If you see some in your area on CL and they are selling it cheap, if it's a bargain, do the chip and gain a new TV.

[Dgtech]

Re: VIZIO VO42L No picture, No Sound

By the way, I'm glad you did do the $6.00 chip instead of the $65 board. Some people replace both master and slave ($120), which isnt neccessary.

[Freezer]

Re: VIZIO VO42L No picture, No Sound

By the way, I'm glad you did do the $6.00 chip instead of the $65 board. Some people replace both master and slave ($120), which isnt neccessary.

For me spending $120 or even $65 was just not an option. I wasn't about to spend that much on a part which may or may not fix the TV. But a $6, that's definitely worth the effort in my book. I am kind of hoping I get to do a repair like this again on another TV/monitor. After having done it once I feel like next time I could do a much better job soldering in the new chip.

Oh, as you suggest I will probably back off the backlight level. I believe I pulled it back to 80% last night. Have to double check.

[hoei]

Re: VIZIO VO42L No picture, No Sound

I just did the same repair. Replaced MOSFET (one broke) and IC. The backlight didnt work at first though, and the IC got very hot. Apparently zenerdiode SZD1 was shorted and replacing this one made the light finally come on

One thing this worries me though is that the IC i still running very hot. It seems that the regulator output of the BD9897 pin 28 is defect, maybe from my first test run when SZD1 was shorted. The output voltage should be 5.8V according to the datasheet instead I get 7.3 V which tells me that the new 7V5 zener diode i put in is actually doing the voltage limitting.

Anyways, the TV's been on for half an hour an still working

[cadillacman]

Re: VIZIO VO42L No picture, No Sound

My latest project is a Vizio VO42LFHDTV10A 42" television. The person I got the TV from said the screen went black but the audio still worked. My first test was the old flashlight into the screen test. I was able to see the image, so I know the problem has something to do with the backlights.

After opening the TV I was surprised by how simple everything looked. I mean I've seen monitors half the size of this TV that have more boards and cables in them. In the middle is the power board, below that is the main video board, and on the left and right are the two inverter boards (sorry I didn't get an overall picture of the TV layout).

From the power board to the inverter boards is a single bundle of wires. According to the silk-screening on the power board the wires were ground, standby, power (either 12V or 24V, I forget which), and 'A' and 'B'. My guess is 'A' and 'B' carry voltage to tell the inverter boards to turn on. First I probed all the wires with the TV in standby. All pins read 0 except 4.9V on the standby lines - so that's as expected. Next I probed the pins with power on. Still 4.9 on the standby, either 12 or 24 on the power lines (again, I forget which), and 'A' and 'B' have 5V and 3.3V. So the voltages coming from the power board appear to be good.

Next I removed the inverter boards for a closer look. When viewing the monitor from the rear, the master board is on the left and the slave board is on the right. The surface mount fuses are good, and the ESR on the caps checks out. Also, the resistance between the different windings of the inverters is consistent, so I'm guessing the inverters are fine. As posted by Dgtech here I checked the mosfets and driver IC. All 4 mosfets on the master board check out. But one of the 4 mosfets on the slave board has a very low reading. So either the mosfet is bad, or the driver IC. Looking more closely at the driver IC I can see the problem. There is a small brown spot and very slight bulge on top of the chip right at pin 26. What's more, pin 26 is gone. I'm guessing the chip literally blew creating the brown spot and ejected the pin from the IC. I've included a close up picture of the bad chip.

So by now I'm convinced the problem that driver IC (BD9897FS). I ended up ordering a new one from the only place I could fine it... eBay. It cost $5.90 including shipping from a distributor in China. The chip arrived in less than 1 week from China (much quicker than I was expecting).

Now the matter of desoldering the old and soldering in the new. I have never done any SMD work, but I do have a nice solder station (Hakko 936) with a small tip. I decided to use ChipQuik SMD Removal Solder as demo'ed in this video. That ChipQuik stuff works great! The chip was off in about 10 seconds. After that a little solder wick the clean up the pads and I was ready to solder in the new chip.

As it turns out, soldering in the replacement was a lot trickier than I was expecting. It took a while to get the chip properly aligned. While soldering I created 2 solder bridges which took a while to clear using solder wick. Once I was finally done I took two close up pictures (see below) of the chip to verify my soldering. By no means a professional job, but considering this is my first ever attempt at SMD soldering I felt it went pretty good. Also, I took a picture of the old chip on top of a dime to give you some perspective of the size.

After all the soldering I put the board back in and the TV works like a charm. I'm going to run the TV for a while to make sure the repair holds, but it looks like for $5.90 in repair parts I have a 42" TV.

Many thanks to the members of this forum. All the knowledge I've gained reading your posts made this possible. And a special thanks to Dgtech for his post!

wow dude your a natural. That looks pretty damn good for a first attempt..good work man

[garylum]

Re: VIZIO VO42L No picture, No Sound

I have the same tv with similar problems. Voltage looks correct coming out of the PS.

I checked resistance across the mosfets and the slave read 8.4k but two on the master read over 10k. Pin 26 on the master IC looks a little discolored. Fusible resister checks out as well. I ordered an ic replacement with mosfets from ebay and I'm going to try and replace them. Soldering the IC on is my biggest worry.
One thing that does trouble me is that I don't see an image on the screen when I shine a flashlight on it. The flashlight isn't flat but rather a half globe tho. Is it possible I'm not getting enough light in there to see the image?
Oh, one other thing. Where is the zener diode on the master board? I ouldn't find szd1 listed anywhere on the board.

[Dgtech]

Re: VIZIO VO42L No picture, No Sound

That chip, is usually my first concern. After that, if the resistances are still bad, change the mosfets.

[garylum]

Re: VIZIO VO42L No picture, No Sound

Yeah, I'm hoping the IC chip will be the culprit. The kit should be delivered today. Off to Fry's tonite to get some chipquik. I also ordered a 45 degree tip for my iron and that should be in by Fri. I figured drag soldering would be the best approach to the IC.

[Freezer]

Re: VIZIO VO42L No picture, No Sound

Hmm, this TV I repaired 5 months ago just died again. I opened the TV up to find the exact same failure as the first time. The chip I replaced "popped" in the exact same place as the first time. Attached are two pictures, the first showing the damage, the second showing the same area after I cleaned the smoke and char off.

My repair worked great, but only lasted 5 months. I'm considering 3 courses of action.

1. Perform the same repair again and hope it lasts longer the second time. The replacement chip was cheap, less than $6.

2. Replace the same chip, but also replace those two caps on the board. Both times this chip failed on the trace that leads to those capacitors. I have checked the ESR of those caps and they check out, however those caps are in parallel and I have not as of yet desolder the caps for an accurate individual ESR reading. So it's possible one of the caps is bad. I also noticed the trace in question passes through the SMD fuse and into that connector which comes from the power board. I guess it's possible the power supply board is sending occasional power spikes which has killed this chip twice.

3. Toss this board and order new master and slave boards. My boards are revision 1.2 and I believe there are 1.3 boards out there, so perhaps the newer board fixes this.


Any suggestions on how to proceed?

Brian

[dumpystig]

Re: VIZIO VO42L No picture, No Sound

I would try option 2 - option 3 seems an expensive way to go without knowing exactly what is causing this failure.

[GbreadMan]

Re: VIZIO VO42L No picture, No Sound

One thread mentions bad V9A caps causing problems in his RCA screen:

https://www.badcaps.net/forum/showthread.php?t=11240

Another thread mentions that V9A's are part of the Samxon GF series which are constantly mentioned by the experts here as lemons and dangerous, although Samxon in general are a good brand.

https://www.badcaps.net/forum/showth...ght=v9a+samxon

I would say replace the caps ASAP, but someone with more experience with caps may be able to assist you better (ie someone who knows markings, colors, etc. of problematic caps).

Dan

[GbreadMan]

Re: VIZIO VO42L No picture, No Sound

BTW awesome soldering job, that looked really professional (before the cap blasted it to pieces again). I've been looking for a better soldering station and that sounds like a good one, I'll have to look into it.

[Dgtech]

Re: VIZIO VO42L No picture, No Sound

One set that I use to have, I did this repair three times. The first time it was the master inverter. Then the slave went about five months later. Then about three months after that the slave went again.

Seeing as the design flaws were causing me to repair this damn thing over and over, I then sold it to someone after doing the last repair. I only sold it for $150 because the front bezel plastic was scuffed up. I could have gotten at least $300 for it if it weren't.

[PlainBill]

Re: VIZIO VO42L No picture, No Sound

This is a common failure with some inverters. I'd read about this modification from LG and see if applies to this inverter. The suggestion to replace the caps is also an excellent idea.

One point: If you have two caps in parallel, the effective ESR is half that of the individual caps. If the measured ESRof the pair is less than half the spec of an individual cap, tehy may be good. However, considering the reputation of this series, I'd replace them anyway.

PlainBill

[Freezer]

Re: VIZIO VO42L No picture, No Sound

Thanks for all the quick replies. I've decided to try replacing the chip again as well as those caps. If it fails again, then I'll try the inverter modification posted by PlainBill.

I did have a question about the replacement capacitors to use. I've replaced a lot of caps over the years, but these are the first "PET" ones I've come across. I believe this means they are polyester film capacitors. Digikey does sell polyester film capacitors, but none anywhere near the voltage and capacitance I need. Can I use aluminum electrolytic low ESR capacitors in this application?

The exact writing on the existing caps is:

V9A
PET
35V
680uF
105 C

Dimensions are 10mm by 21mm.

I'm considering the following Panasonic FM series as the replacement:

http://search.digikey.com/scripts/Dk...name=P12417-ND

The diameter is slightly larger, but I have room to work with.

[PlainBill]

Re: VIZIO VO42L No picture, No Sound

Thanks for all the quick replies. I've decided to try replacing the chip again as well as those caps. If it fails again, then I'll try the inverter modification posted by PlainBill.

I did have a question about the replacement capacitors to use. I've replaced a lot of caps over the years, but these are the first "PET" ones I've come across. I believe this means they are polyester film capacitors. Digikey does sell polyester film capacitors, but none anywhere near the voltage and capacitance I need. Can I use aluminum electrolytic low ESR capacitors in this application?

The exact writing on the existing caps is:

V9A
PET
35V
680uF
105 C

Dimensions are 10mm by 21mm.

I'm considering the following Panasonic FM series as the replacement:

http://search.digikey.com/scripts/Dk...name=P12417-ND

The diameter is slightly larger, but I have room to work with.

If I recall correctly, PET is Polyethylene terephthalate the material used in the sleeve. And Panasonic FMs should be a good choice.

I would also suggest you seriously consider making the modification. LG & Philips came up with that because they realized there was a design problem.

PlainBill

[GbreadMan]

Re: VIZIO VO42L No picture, No Sound

You might also want to consider inspecting and/or replacing those K4075 mosfets at the bottom of the screen.

Maybe you can install a super-tiny heatsink on the IC without shorting it? Something from an old 8086, perhaps?

Dan

[Freezer]

Re: VIZIO VO42L No picture, No Sound

I would also suggest you seriously consider making the modification. LG & Philips came up with that because they realized there was a design problem.

I've decided to go with the inverter modification after all. It doesn't appear to be that difficult, certainly easier than soldering in the replacement SMD IC.

Can anyone help me to identify the correct parts to order, the PDF is a little vague.

Zener Diode
The PDF says I need two "TVS zenerdiode (33 V)." The PDF also says I can use unidirectional or bidirectional. My plan is to use bidirectional just so I can't screw that up. I found TVS zener diodes on digikey, and I can filter them down by bidirectional, SMD, and in stock. However, for voltage I can choose from "Voltage - Reverse Standoff (Typ)" and "Voltage - Breakdown." Which one do I set to 33V?

Capacitors
For capacitors I need two "MLCC capacitor (100 pF)." I believe MLCC stands for "Multi-Layer Ceramic Capacitor" so I've been looking inside digikey's "ceramic" section under capacitors. Again filtering by 100pF, SMD, and in stock yields 21 pages of caps to choose from. It would help if I knew the voltage. Should I just pick something that should be safe, maybe 50V?

Resistors
The final components are resistors. I've decided to go with SMD instead of the other option presented in the PDF. So I'm looking for four SMD 4.7 ohm resistors. I've found 11 pages of resistors to choose from. The PDF has no indication of power (W).

Even though it would cost more, I would order this repair kit if I could (to ensure I get the correct components). However the only place I've found selling the repair kit is from the U.K. which doesn't help me much here in California.

[PlainBill]

Re: VIZIO VO42L No picture, No Sound

Zener - Reverse standoff. And I'd go with a 600 milliwatt (the selector says watt, but that's ridiculous).

Capacitor - 50 volt should be OK, but why not be safe and go with 100 volt? Also, if you select 'cut tape' you will eliminate 2/3 of the hits.

Resistor - 1/8 watt should be sufficient, but it will up the price from $.02 each to $.06 each if you go with 1/4 watt.

PlainBill