Sony Bravia KLV-40U100M no power to anything

[Skoffer]

Ok, I have this TV. When I plug it in and push the power button, I get nothing.

I have read different threads on these Sony tvs and everyone says that if you get the secondary 5Vs, then it is probably the logic board.

Well, I have marked in the picture where I am getting voltage on the connector from the power supply to the logic board. I get 4.77V when Logic board is plugged in and an even 5V when it isn't plugged in.

I have also marked where the power button connects to the logic board and I get 4.77V when it isn't pressed and it goes to 0Vs when it is held down. I assume that is normal.

What else do I need to test on this thing to detemine why it won't turn on at all? Thank you for you help.

[Dgtech]

Re: Sony Bravia KLV-40U100M no power to anything

Well, I have marked in the picture where I am getting voltage on the connector from the power supply to the logic board.

You forgot to include the picture.

[Skoffer]

Re: Sony Bravia KLV-40U100M no power to anything

You forgot to include the picture.

Sorry, they failed on me because they were too big. I didn't realize it till I posted.


EDIT - Ok, I made that a lot more difficult than it needed to be. Sorry about the delay.

[PlainBill]

Re: Sony Bravia KLV-40U100M no power to anything

Ok, I have this TV. When I plug it in and push the power button, I get nothing.

I have read different threads on these Sony tvs and everyone says that if you get the secondary 5Vs, then it is probably the logic board.

Well, I have marked in the picture where I am getting voltage on the connector from the power supply to the logic board. I get 4.77V when Logic board is plugged in and an even 5V when it isn't plugged in.

I have also marked where the power button connects to the logic board and I get 4.77V when it isn't pressed and it goes to 0Vs when it is held down. I assume that is normal.

What else do I need to test on this thing to detemine why it won't turn on at all? Thank you for you help.

The service manual is available at Electrotanya.

Do any of the connectors on either the power supply or the main board have legends indicating the functions of the pins? Specifically, we are looking for a pin labeled something like PS_ON, or something similar.

If you can't locate a pin like that, I suggest monitoring each pin on the two connectors in the lower left end of the main board while you press the power switch several times. You are looking for a pin that switches from 0V to about 3.3V and back. This should be the PS_ON control.

It may not be obvious, but the power supply is actually two supplies in one. The standby supply is on whenever the TV is plugged in. The standby processor (on the main board) turns on the main supply when the power button is pressed. Obviously, if the PS_ON signal is not generated by the main board, the main board is PROBABLY suspect. (On some TVs you can set an option to disable either the remote or the control panel). If the PS_ON signal IS generated, but the main section of the power supply does not turn on, obviously the poser supply is suspect.

PlainBill

[Skoffer]

Re: Sony Bravia KLV-40U100M no power to anything

PlainBill, Thank You!

I don't understand everything in that service manual, but I think I understand enough. Knowing what voltages I should be seeing should really help me narrow this down.

But, the first thing I am going to do is program a Universal remote for this TV and see if it comes on from the remote power. I don't have the original remote for the TV. I never would have thought you could actually turn off the TVs keyboard.

[PlainBill]

Re: Sony Bravia KLV-40U100M no power to anything

PlainBill, Thank You!

I don't understand everything in that service manual, but I think I understand enough. Knowing what voltages I should be seeing should really help me narrow this down.

But, the first thing I am going to do is program a Universal remote for this TV and see if it comes on from the remote power. I don't have the original remote for the TV. I never would have thought you could actually turn off the TVs keyboard.

I was similarly unenlightened, then in a recent thread someone had spent hours troubleshooting a TV before discovering the front panel was disabled. The brand? Sony!

PlainBill

[fleetwise]

Re: Sony Bravia KLV-40U100M no power to anything

That would be me. I just never dreamed someone would put a perfectly good plasma in the trash. The remote will be here in the next day or two so I will find out if it is just settings or another problem. All I can see it being though after wasting hours testing it all

[Skoffer]

Re: Sony Bravia KLV-40U100M no power to anything

Ok, so according the the service manual, the PC_ON pin should be pin 1 on the 8-pin connector between the main board and the power supply.

Pin 8 on this connector is the standby which I am getting the 4.77v.

I am getting a constant 0.01v on the pin 1 even when I press the power button over and over.
So it is looking like there is a problem with the mainboard.

hoping to anticipate a suggestion, I recorded the ohms on the mosfets. My readings are on the attached excel file. Or if you can decipher the following.
1/2 refers to pins 1 to 2, 1/3 refers to pins 1 to 3, 2/3 refers to pins 2 to 3.

mosfet # ---------1/2 1/3 2/3
1084-33pm 404I2 -240 334 358
1084-25 0545al ---351 43K 41K
1084-18PM 300CC 164 241 403
1084-18PM 300CC 158 40K 38K
1084-33pm 404I2 289 474 762

I honestly don't know what that means. Where should I go from here?

[PlainBill]

Re: Sony Bravia KLV-40U100M no power to anything

Ok, so according the the service manual, the PC_ON pin should be pin 1 on the 8-pin connector between the main board and the power supply.

Pin 8 on this connector is the standby which I am getting the 4.77v.

I am getting a constant 0.01v on the pin 1 even when I press the power button over and over.
So it is looking like there is a problem with the mainboard.

hoping to anticipate a suggestion, I recorded the ohms on the mosfets. My readings are on the attached excel file. Or if you can decipher the following.
1/2 refers to pins 1 to 2, 1/3 refers to pins 1 to 3, 2/3 refers to pins 2 to 3.

mosfet # ---------1/2 1/3 2/3
1084-33pm 404I2 -240 334 358
1084-25 0545al ---351 43K 41K
1084-18PM 300CC 164 241 403
1084-18PM 300CC 158 40K 38K
1084-33pm 404I2 289 474 762

I honestly don't know what that means. Where should I go from here?

OK, that's your first problem / opportunity. Those aren't mosfets, they are LDO regulators. Also, there is a 6th LDO regulator, U11.

Note U20. One of the pins is labeled IN (for Input), the other G (for Ground). While it doesn't appear to be labeled, the tab is the output.

The first step would be to plug it in and verify you have the 5V standby (4.77 volts) coming to the board. Then check the IN pin on each of those regulators. One of them should show about 4.77 volts. Then check the output voltage of those that have an input voltage (The two digits after the dash indicate the output voltage). If you don't find any that have an input voltage, things are really looking up!!!

The next step would be to look over the board carefully, looking for a component whose identifier starts with F (for fuse).

If things get really desperate, there is someone on eBay who will repair it for $80. That tells me it is something fairly simple.

PlainBill

[Skoffer]

Re: Sony Bravia KLV-40U100M no power to anything

XXX - In - Out
U11 - 0.45v - 0v
U17 - 4.75v - 3.28v
U18 - 4.48v - 2.47
U19 - 2.96v - 1.78v
U20 - 0v - 0v
U21 - 0v - 0v

On the ones with voltage in, the outputs all match the number on top. Except U11, which was only showing .45v in and nothing out.

I found a few spots on the board the have FB then a number. Are those fuses? I couldn't find any that started with just an F. I looked the board over 3 times.

Oh, and in case you were wondering, I tried programming a universal remote I have with the sony code in the manual, it only had 1, and the tv still wouldn't turn on. So, either that 1 code doesn't work at all, and I need a real remote, or that isn't the issue.

EDIT - Actually, I forgot about my direct tv remote. I went through all of it's codes and got nothing from the tv, so I'm pretty sure it has nothing to do with the remote or keyboard being toggled off.

[PlainBill]

Re: Sony Bravia KLV-40U100M no power to anything

XXX - In - Out
U11 - 0.45v - 0v
U17 - 4.75v - 3.28v
U18 - 4.48v - 2.47
U19 - 2.96v - 1.78v
U20 - 0v - 0v
U21 - 0v - 0v

On the ones with voltage in, the outputs all match the number on top. Except U11, which was only showing .45v in and nothing out.

I found a few spots on the board the have FB then a number. Are those fuses? I couldn't find any that started with just an F. I looked the board over 3 times.

Oh, and in case you were wondering, I tried programming a universal remote I have with the sony code in the manual, it only had 1, and the tv still wouldn't turn on. So, either that 1 code doesn't work at all, and I need a real remote, or that isn't the issue.

EDIT - Actually, I forgot about my direct tv remote. I went through all of it's codes and got nothing from the tv, so I'm pretty sure it has nothing to do with the remote or keyboard being toggled off.

The .45 volts into U11 is interesting, but it may not be significant. What I find interesting is the power supply output is 4.77 when load is present, 5.00 volts with no load. Usually regulation is better than that. I wonder if something is loading the power supply.

FB stands for ferrite bead. It suppresses electronic noise.

I'd suggest doing more research. The eBay auction suggests this is a known problem with a fairly simple solution. Maybe one of the regulars or irregulars will chime in with a clue.

PlainBill

[Skoffer]

Re: Sony Bravia KLV-40U100M no power to anything

I found a solution that fixed the TV. At U24 there is some type of microprocessor that controls the reset. Apparently it is a very common problem for this to fail and fry itself. Apparently it isn't a detrimental component to the operation of the TV.

I desoldered it from the board and voila...TV works perfectly now.

I found this solution here.

There is a review by a user named Roundabout57 who gives this solution to the problem.

I'd say this is a success. Maybe someone else can benefit from this.

[PlainBill]

Re: Sony Bravia KLV-40U100M no power to anything

Good job!! The reset controller strikes again. This is a common problem on certain monitors. I suspect this is another case where the processor has an integrated reset controller, but the designer added an external one.

PlainBill

[rmoody]

Re: Sony Bravia KLV-40U100M no power to anything

Thank you Mr. Skoffer for sharing this. It worked for me as well on a friends tv. It's always nice to do a quick fix like that. I'm gonna post the information here as well.

"I recently acquired one of these TV's from a friend who didn't want to pay for repairs. I was a technician with Sony for many years and while I have not repaired this product specifically, I decided to tackle the problem. This unit was dead, just like many others have reported. To begin, check the 5v line at pin 8 of CN19. If it is present, check for 3.3v at SW1 (the reset switch, which was not installed on these units). There will be foil traces on the board where the switch would have been located, just place your meter probes across these points. If the 3.3v is not present, then the cause is most likely the U24 Microprocessor Reset IC. This is a small three leg device (two legs on one side, one on the other), it is fairly close to the large Genesis CPU on the board. On my set, this Reset IC had a crack in it that was hard to see without a magnifying glass. As this part begins to fail, it causes an intemittent power on/off problem until the TV finally just stops working when the IC completely shorts out.

Since I didn't have the part available, I just removed the part from the board and the set came back to life. You can fix the TV by just removing the part, however, it may come on sometime in a random mode due to the lack of a reset pulse to the CPU. So far, mine has worked perfectly without this IC. I've done a little research and found out that Sony does not sell this part, they want to sell you the entire board for a small component failure! People on Ebay are selling "repaired" boards, most likely they are also just removing the IC and charging $75 - $100 to do it. This part, ASM810JEURF, is not available in small quantities anywhere that I've been able to find."