Sanyo DP46849 Backlight Issues

[Thorsbolt]

Picked up a 46" Sanyo from a needy family. Works great for 20 mins or so, then backlight goes out. Still have sound. Upon restarting picture shows back up for 5 min then screen cuts out. If I let it cool down it will stay on longer. Could this be CFL's wearing out and drawing to much juice when warmed up. Let me know where to start and I'll post any pictures requested.

[newtothis]

Re: Sanyo DP46849 Backlight Issues

Pictures of all boards and overall layout, Get a clear picture of the labels next to the connector going from the PSU to main.

We will be going through some voltage readings with a DMM to see what is dropping out when you lose the backlights

[Thorsbolt]

Re: Sanyo DP46849 Backlight Issues

Ok, I work till 10:00, but took some pictures before I left. I'll take it apart more tonight and get more.

[Thorsbolt]

Re: Sanyo DP46849 Backlight Issues

Its almost impossible to test the invertor board on this unit. The Power Supply and Video Boards bolt to the back panel and the Invertor Board bolts under the panel. Testing while powered up is going to be a task. Taking new pictures now, because I realized that some were terrible.

[newtothis]

Re: Sanyo DP46849 Backlight Issues

Ignore the invertors for now, We need to check voltages on the PSU first.

Meter set to 20VDC can you test the BL_ON pin when the backlights fail.

[stj]

Re: Sanyo DP46849 Backlight Issues

check for cracked soldering on the power and invertor boards.

it sounds thermal and that usually ends up being fractured soldering.

[jetadm123]

Re: Sanyo DP46849 Backlight Issues

As mention by stj, it appears to be a thermal problem. Try heating up each board with a hair dryer while the tv is running to see if you can accelerate the shutdown process. This will hopefully help you narrow the board that's causing the problem.

[Thorsbolt]

Re: Sanyo DP46849 Backlight Issues

I agree with the Thermal Diag. While working the BL On reads 3.27V DC.
Failed it reads the same.

[newtothis]

Re: Sanyo DP46849 Backlight Issues

Yeah seems to be thermal

[Thorsbolt]

Re: Sanyo DP46849 Backlight Issues

I'm gonna hit the power supply and video boards with a hair dryer tonight, but the invertor board is buried. Is there a good way to ohm test it?

[Thorsbolt]

Re: Sanyo DP46849 Backlight Issues

Better pics to help diag.

[Thorsbolt]

Re: Sanyo DP46849 Backlight Issues

These 3 are of the back of the power board. I see no compromised solder but I did see too slightly discolored spots.

[stj]

Re: Sanyo DP46849 Backlight Issues

some bad joints there.

look for faint rings around the joints like a halo

[Thorsbolt]

Re: Sanyo DP46849 Backlight Issues

Well I can see alot of bad solder joints, what I also see is what look like something was spilled on the board. What should I use to clean it and should I focus on fixing all the solder joints or getting a new board?

[stj]

Re: Sanyo DP46849 Backlight Issues

fix the joints and then clean the flux off with IPA

fixing joints costs nothing, so it's always worth a try.

[Thorsbolt]

Re: Sanyo DP46849 Backlight Issues

I fixed some solder and cleaned the board. TV still shuts down, but I am able to access the invertor now when it's powered up. Any further testing?

[Thorsbolt]

Re: Sanyo DP46849 Backlight Issues

Also the three steel bars get exceptionally hot on the back of the power board. Like they'd burn you. I'm pretty sure the for heat dissipation. But should they get that hot?

[Thorsbolt]

Re: Sanyo DP46849 Backlight Issues

I ran a very low CFM fan over different boards to keep them cool and found the Main Board beneath a heat shield is getting to hot and shutting it down. It seams a finned block of metal had afoam strip on it to protect the board... It was holding heat. I removed it and the TV stays on. I'm still monitoring it. I will send a picture.