I am repairing a Vizio LCD TV TCON board. I am unable to find a cross reference or data sheet for a failed semiconductor. The part is not referenced in the service materials referenced on this site. So, I an unable to select a suitable replacement. The TV model is the infamous VX37L HDTV 10A. It has the AU Optronics panel and TCON board.
Model on the TCON is: TS-5337T03021-740-NE40000. The offending part is Q303, part number engraved is: 25709. It has a base to collector short. Base polarity is negative (continuity to the ground plane of the board). I have lots of various scrap boards so I could scavenge a suitable substitute if I knew a bit about the specs for the original transistor. Any help on this is greatly appriciated.
Just to add to the site knowledge base, the Vizio logo lit up with the correct amber to white transition. But the backlight shut down immediately, and the screen was ALWAYS BLACK. Even when the backlight came on briefly during the power on self test. So the TCON was never allowing any light to pass thru the LCD panel. I substituted the TCON board with a working test-board and the set works correctly.
Next, I checked th TCON board on the bench. OK on the visual inspection. I then used the multi-meter in continuity mode (diode check mode on my B7K Precision 2408 workhorse). All fuses OK. Then I began checking all the surface mount caps for shorts. I read about this on the forum on a post troubleshooting a TCON board that wad pulling the supply rail to near zero. I now routinely do this check.
And guess what? Several caps showed shorted. So I pulled one-at-a-time and checked them and the board pads to see if the short cleared. Nope. I traced the circuit path and began looking for the short. I found Q303 B to C shorted.
Pulled the transistor and the short cleared. Now if I can replace offending chip with a good substitute, I can retain my testing TCON board and save buying a replacement. I suspect it is a simple switching PNP type, but I just do not know for sure.
I hope this helps others diagnose their problem circuits. The forum has been a great help to me. I have salvaged about 100 monitors and TVs. The bad-cappers are the easy ones. I now go after the tougher fixes. Keeps my old-geezer mind sharp as an Xacto knife. Cheers.
Model on the TCON is: TS-5337T03021-740-NE40000. The offending part is Q303, part number engraved is: 25709. It has a base to collector short. Base polarity is negative (continuity to the ground plane of the board). I have lots of various scrap boards so I could scavenge a suitable substitute if I knew a bit about the specs for the original transistor. Any help on this is greatly appriciated.
Just to add to the site knowledge base, the Vizio logo lit up with the correct amber to white transition. But the backlight shut down immediately, and the screen was ALWAYS BLACK. Even when the backlight came on briefly during the power on self test. So the TCON was never allowing any light to pass thru the LCD panel. I substituted the TCON board with a working test-board and the set works correctly.
Next, I checked th TCON board on the bench. OK on the visual inspection. I then used the multi-meter in continuity mode (diode check mode on my B7K Precision 2408 workhorse). All fuses OK. Then I began checking all the surface mount caps for shorts. I read about this on the forum on a post troubleshooting a TCON board that wad pulling the supply rail to near zero. I now routinely do this check.
And guess what? Several caps showed shorted. So I pulled one-at-a-time and checked them and the board pads to see if the short cleared. Nope. I traced the circuit path and began looking for the short. I found Q303 B to C shorted.
Pulled the transistor and the short cleared. Now if I can replace offending chip with a good substitute, I can retain my testing TCON board and save buying a replacement. I suspect it is a simple switching PNP type, but I just do not know for sure.
I hope this helps others diagnose their problem circuits. The forum has been a great help to me. I have salvaged about 100 monitors and TVs. The bad-cappers are the easy ones. I now go after the tougher fixes. Keeps my old-geezer mind sharp as an Xacto knife. Cheers.
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