Sony KDL40W4100: no signs of life?

[whyexactly]

Hey guys, I'm trying to repair this TV that does absolutely nothing. No LEDs, no clicks or whines or anything, I've tried both the remote and the physical power button. Apparently Best Buy diagnosed it as a bad power supply but I'm not convinced that's the case. The 3.3V standby from the power supply to the main board is good, so from a bit of searching the main board is the more likely culprit. Suggestions on where to check from here would be greatly appreciated, if you need more details or pictures or anything at all from my side just let me know

[RJARRRPCGP]

Re: Sony KDL40W4100: no signs of life?

Hey guys, I'm trying to repair this TV that does absolutely nothing. No LEDs, no clicks or whines or anything. Apparently Best Buy diagnosed it as a bad power supply but I'm not convinced that's the case. The 3.3V standby from the power supply to the main board is good, so from a bit of searching the main board is the more likely culprit. Suggestions on where to check from here would be greatly appreciated, if you need more details or pictures or anything at all from my side just let me know

Well, it could be a PCB problem, especially with the tv being dead like the horsefly that landed on your chest...

[CapLeaker]

Re: Sony KDL40W4100: no signs of life?

If you have standby voltage going to the main board and the main board does not respond, then you certainly have a main board problem.

[whyexactly]

Re: Sony KDL40W4100: no signs of life?

Ok good to know, thanks! What's my probability of success trying to troubleshoot and repair a main board? Decent odds or pretty much hopeless?

Here's the two stickers on the board, I'm not sure if the sticker on the tuner just applies to the tuner or to the whole board. Apologies for the less than stellar pictures, all I have is my phone. I can type up any of the letters/numbers that are unclear if needed.

[whyexactly]

Re: Sony KDL40W4100: no signs of life?

I figured I'd give the obvious a shot and check any fuses I could find, they all tested good but one looks to be missing? It's labelled F2002, the service manual shows a component in that spot but I'm not experienced enough to recognize if the board looks like the component came off or if it was intentionally not installed.



edit: it's not in the parts list, so I'm thinking not installed from the factory?

[CapLeaker]

Re: Sony KDL40W4100: no signs of life?

There isn't much you can do with a broken main board. You'd need a hot air rework station and a schematic. As for now, all you can try is to hear up the main board with a hair dryer and see if that brings it to life. You can also try freeze the board (can of air upside down) and see what that's gives. You can also check that none of the power rails on the main board are shorted to GND and that the voltage regulators are giving proper voltage. The main IC usually does all the turning on, off etc. So chances to repair that board is slim.

[weeb0]

Re: Sony KDL40W4100: no signs of life?

@CapLeaker : It is the first time I can hear someone talking about freezing a pcb. It is interesting.

@WhyExactly: If the part is not in the BOM, so it is normal there is no fuse installed. Also, in the schematic, if the part begin with NC usually it will not be populated on the pcb. Often it is desirable to reuse the same pcb for multiple products.

Also, did you check the voltage of the POWER_ON signal ? Did you read all the signal from the connector going to the controller board ?

[whyexactly]

Re: Sony KDL40W4100: no signs of life?

I haven't got a reflow station unfortunately but I have got a heat gun and the schematics so I'll give it a shot, it's already damaged so not a big risk. For the power supply regulators I didn't realize I'd still see voltages with the unit off, I'll check those next.

As for the fuses that aren't on the board they're only shown on the layout diagrams (I think that's the name, it's like an exact digital layout of both sides of the board), when I used the find tool they didn't show up in the BOM or schematics.

The only voltage I checked properly was the 3.3V standby, I wasn't sure if anything else would show a voltage with the unit off, I didn't notice the other voltages have their own grounds until later.

[CapLeaker]

Re: Sony KDL40W4100: no signs of life?

3.3v STBY is generated on the PSU and is always there. That goes to the main board. When you turn the tv on, the main board returns PSON and BLon to the power supply and that turns on all the voltage rails and the backlight, the tv turns on.

So yeah, not everything runs on 3.3v on the main board and different voltages are needed.

You can test the power supply by only connecting the backlights to it and have everything else unplugged. You need 2 X 1k ohm resistors. One between STBY voltage and PSON, the other between STBY voltage and BLon. Plug it in and the PSU should be up and runnning.

[syaoran123]

Re: Sony KDL40W4100: no signs of life?

did you check underneath the power supply board for any charring/burning? I once spotted some charring on one of the transformer legs and exploded the solder off it. Luckily no components were damaged, just a quick resolder did the trick.

[whyexactly]

Re: Sony KDL40W4100: no signs of life?

I hooked up the resistors and all the 12V and 15V pins going from the PSU to the main board have the correct voltage, the only pin on that connection that I don't know what to expect on is called AC_OFF_DET. I ran out of time so I'll check the backlight this evening. I know they're a high voltage but the schematic doesn't show what the actual voltage is supposed to be.

[dick_barton]

Re: Sony KDL40W4100: no signs of life?

What is the all the dark looking stuff covering quite if the bit of the board in attachment 136762?

[dick_barton]

Re: Sony KDL40W4100: no signs of life?

AC detect should be I believe >2V

[whyexactly]

Re: Sony KDL40W4100: no signs of life?

There doesn't look to be anything on it, that's just how some darker sections of the board turned out in the picture.

[whyexactly]

Re: Sony KDL40W4100: no signs of life?

AC_OFF_DET read no DC voltage, and HV1 to HV2 only read ~6.4VAC on the PSU side with the backlight unplugged, so I'm not sure if I'm doing something incorrectly as that doesn't exactly seem high. I noticed there's a "DIMMER" pin next to the BLon pin so I'm not sure if I need to do something with that as well.

The PSU looks to be good on the back side, again apologies for my crummy phone camera, it's very hit and miss on quality.

[CapLeaker]

Re: Sony KDL40W4100: no signs of life?

Jump BLOn over to the DIM pin too. See if it comes on now.

[whyexactly]

Re: Sony KDL40W4100: no signs of life?

No difference that I could see unfortunately. I have a similar TV here (Sony KDL40S4100). Assuming the plugs are the same, should it be possible to use that PSU to test the backlight and inverter? I'm guessing the voltage to the inverter should be pretty standard?

[cliff_hootarski]

Re: Sony KDL40W4100: no signs of life?

Do not try to measure HV1 or HV2 with a regular DMM, you will destroy your meter if the voltages are actually there!

[whyexactly]

Re: Sony KDL40W4100: no signs of life?

Good to know! It's a pretty nice Greenlee so I'd hate to ruin it.

[ReeceyBurger123]

Re: Sony KDL40W4100: no signs of life?

Resolder the little smd caps on the bottom side of the mainboard, should sort it. I have had this before on this chassis.