Vizio VX37L TCON Transistor ID please

[G Nicholls]

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.

[budm]

Re: Vizio VX37L TCON Transistor ID please

Since you have working T-CON, it should be fairly easy to find out if that transistor is PNP or NPN by using the meter in Diode testing mode. Since it is small signal transistor, you can use through hole transistor in TO-92 case to use as a sub, such as 2N3904, 3906.

[G Nicholls]

Re: Vizio VX37L TCON Transistor ID please

Thanx, budm. I realize I may be able to try to hack a fix to this TCON. I was hoping someone might know the correct cross reference or a known substitute.

If I repair this TCON and turn it out, I would not like it to bounce-back due to a too marginal repair. Can you tell what function this transistor preforms? I was not sure if this was a switching or timing circuit. Could make a difference in the selection of a replacement.

Thanx for all your participation at the site. I have learned a lot of great info.

[kevinm34232]

Re: Vizio VX37L TCON Transistor ID please

I think you may have gotten the tcon board # wrong, is this your board:?

http://www.shopjimmy.com/auo-55-37t0...-con-board.htm

If so you can find on ebay relatively cheap:

http://www.ebay.com/sch/i.html?_odkw...3.021&_sacat=0

I personally have found it very difficult to find schematics or anything for these boards..

[budm]

Re: Vizio VX37L TCON Transistor ID please

That Q303 is sitting in the AVDD switching power supply section, so more likely to be used as a switch.
The high frequency video signals are handled by the IC's. You can measure the Voltage on the Collector to see about how high the voltage is being applied to it.

[G Nicholls]

Re: Vizio VX37L TCON Transistor ID please

Mornin' Budm. I pulled the working TCON board and checked the good Q303. Part number ia 25727 on this one (must be a in house number). In diode test mode the meter shows infinate across all lead combinations except base to collector. That shows .534 with the + probe on the base and - on the collector. That is within the typical forward bias range this meter shows on diodes and transistors.

I wonder if this is a complex transistor with a zener diode trigger or some other exotic design. Don't know, so I buttoned-up the unit with my testing board and sent it on it's way. Works fine.

I will repair the bad TCON when I get a suitable replacement transistor. Another bad AU OPTO TCON is sure to pass thru here sometime. Might have the needed salvageable part.