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Sanyo DP40142 LED/LCD TV Repair
I was watching my Sanyo DP40142 LED/LCD 40” TV the other day, and the screen just went black! I got my flashlight and checked the screen to see if the panel also went out, but it was still working, praise The Lord! So I knew that the problem was just affecting the backlight.
I went to turn on my vacuum cleaner to vacuum the dust off of the TV and my vacuum cleaner quit and tripped the breaker, as I mentioned in the previous article on my Hakko FX-888D soldering iron repair.
So the first thing I did after checking the screen and taking the back off of the TV was to look the boards over good, and start checking voltages.
The voltages checked fine. The TV is not shutting down so I would imagine that there are no short circuits.
Here are some photos showing the IR board and Mainboard. The T-Con is integrated into the Zoran ZR748 SupraHD SoC, on the mainboard. The LED driver board must be inside the LCD module. I’m not sure why Sanyo calls it a LCD module. I would call it the LCD case.
Above are the Schottky Barrier Diodes and N-Channel Enhancement-Mode QFET/MOSFET’s. I removed them to put some fresh thermal compound on them. I also did the same with the Bridge Rectifier, which you can see in the next photo. The TV is six years old, so it’s a good idea to freshen up the thermal compound.
In the photo above I am checking the voltage on the backlight DIM line with my amazing Brymen BM869s DMM and noticed that there is a 1.580V AC signal on it. I checked the connector on the mainboard to verify that the signal was coming from the mainboard and not the IR board, and it was.
I checked the AC signal with my Tek 2465A-DV oscilloscope. You can see in the next photo that the signal is a nice PWM square wave running at 119.9989Hz.
In the photo above, I am checking the square wave signal with my small inexpensive JYE Tech DSO Shell Digital kit oscilloscope that I bought awhile back. It is reading the signal at 120.064Hz with a Duty Cycle of 62.4%. That is only 0.0651Hz off from my Tek scope. Not too shabby for an inexpensive little digital kit scope! I didn’t check the duty cycle with my Tek scope, but that looks about right judging from the graticules.
You will notice a vertical white line on the little DSO Shell scope display screen. If the seller had googled my name, they would have seen that I write electronics repair articles and that the scope could appear in one of my articles. They would have made sure that the screen they sent to me was perfect.
Or, maybe they sent it on purpose, hoping that I would repair it and write an article about it. Who knows?
After I get my oscilloscope taken care of, and build some test equipment that I need to build, I might look into repairing it. It does kind of get on my nerves.
I decided to upgrade the primary filter cap with a low ESR Nichicon 105⁰C E-Cap. The new E-cap is quite a bit larger than the original and is rated 30 volts higher. It hangs off of the IR board a little bit, but that is no problem. There is plenty of room.
I put some clear indoor adhesive onto the E-cap to help hold it in place and give the leads some strain relief. The other e-caps look good.
In the photo above, I am testing the LED backlight with my TKDMR Model #TD3H backlight/component tester. There is no light emanating through the back of the LCD module.
I have the LCD screen and diffusers removed from the case and stacked onto a table. I taped the LCD panel board carefully onto the LCD screen with masking tape to keep from damaging the TFT’s. Masking tape is pretty easy to remove and doesn’t leave a bunch of adhesive on things.
I don’t trust suction cups much, so I used a piece of ply board with a thick towel over it to slide the LCD screen onto so I could remove it from the LCD module and carry it to the table safely. It worked out great.
Everything is removed and you can see the LED driver board inside the LCD module. I’m ready to remove it from the module and start checking the LED strips.
With my backlight tester hooked up to light all of the LED strips, they did not light. After removing the first strips, (A) and (C) [that were hooked end to end with a small coupler], the rest of the strips lit up just fine. So I know that the problem is somewhere in one or both of the (A) or (C) strips, and that the LED driver board is probably ok.
The very first LED on the (A) strip would not light, and the third and fourth LED’s would light up weak and sporadically because of cold solder joints. I went ahead and fluxed/re-soldered all of the LED’s on the (A) strip with my soldering iron.
The LED’s lit up great on the (C) strip, but one connector pad that couples into the (A) strip through the coupler, had a little burn mark on it. The spring-pin for that pad inside of its coupler wasn’t sprung down well enough to make good contact with the contact pad either. I forgot to take a photo of it.
So I cleaned up the pad with emery cloth and alcohol and reached inside the coupler with a needle and bent the little spring-pin down some so it will make better contact with the connector pad.
In the photo above I am letting the adhesive set up on the LED light refractors for several hours. I forgot to get some Super Glue gel the last time I was at the store, so I used some small dots of E6000 adhesive to hold them down. I’ll go ahead and re-solder the LED’s on all of the strips if I have problems with the LED strips again.
Success!! The LED’s are working great! I repaired my TV and it didn’t cost me an arm and a leg! With the LED backlight tester outputting 122V at 59mA, the softly lit LED’s make a beautiful picture! Mr. Yong may choose to use this photo for the articles thumbnail!
Now my Sanyo 40” LED/LCD TV is back together and lighting the LED’s very well. We can see some light emanating from the LCD module.
Looking from the back of my adjustable-top TV repair table, we can see the TV showing the Star Trek movie through the tempered glass. It looks like another successful repair is in the books. Now it is time for me to rebuild the fan motor and upgrade my Tektronics 2465A DV oscilloscope, and then start building some nice electronics test equipment. Till next time – take care, guys!
Please leave any comments or suggestions that you may have below. Thanks!
Robert Calk Jr., is a Hobbyist from the U.S.A. that loves Electronics Device Repair.
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