Sanyo DP42647-00 DP42647 No Picture, Has Backlight & Sound

[kevinm34232]

I suspected the T-Con so I first checked voltage at the Fuse F1 and had only 1.5V on both sides. Checked the main board side same thing. I disconnected the LVDS cable from the T-Con and now I had 12V coming from the main board.

I froze the board and immediately see Q303 melting. It shows short between all legs in circuit. The best I can tell the stamp on it says "25719". I googled that and couldn't find it.

Can anyone help with this? Thanks!

[kevinm34232]

Re: Sanyo DP42647-00 DP42647 No Picture, Has Backlight & Sound

I found another thread on this T-Con with same problem, that part was never found it looks like.

https://www.badcaps.net/forum/showthread.php?t=24237

Is there a way I could attempt to replace with another transistor, I have a bag of assorted thru hole transistors from Radio Shack. Im just not sure how I'd know what type it is and what leg would go where.

Could anyone tell by just looking at the traces on the board?

[tom66]

Re: Sanyo DP42647-00 DP42647 No Picture, Has Backlight & Sound

I would guess it is an NPN transistor, top left pin is base, bottom left is collector, right is emitter.

[kevinm34232]

Re: Sanyo DP42647-00 DP42647 No Picture, Has Backlight & Sound

OK I tried a 2N3904 using those pin connections. The short is gone, 12V is back, but still no pic. Here are the voltages at the pins:

B-1V
C-16V
E-0.7V

Could the pin layout be different?

[kevinm34232]

Re: Sanyo DP42647-00 DP42647 No Picture, Has Backlight & Sound

Is it worth trying to switch the leads around or would that do damage. Tom were you pretty confident in your suggestion? Is the 2N3904 adequate?

[tom66]

Re: Sanyo DP42647-00 DP42647 No Picture, Has Backlight & Sound

Could be PNP with C-E reversed, but less likely. I would make sure to remove panel ribbons while trying any of these.

[kevinm34232]

Re: Sanyo DP42647-00 DP42647 No Picture, Has Backlight & Sound

Ok I can try that. Not sure if this tells you anything, but the cathode side of diode D302 below Q303 has around 16V and traces to the bottom left leg of Q303.

[tom66]

Re: Sanyo DP42647-00 DP42647 No Picture, Has Backlight & Sound

Yes, you can see the board layout, the top left is high impedance, because of the two resistors. So it is probably not C or E, more likely B. The bottom left is probably the input, because it's coming from the AVDD source (15~16V, around 1A, for LCD source drivers), and the right is probably the output, because it's feeding into those capacitors for some local voltage source (possibly a buffer source for AVDD or VGH...)

[kevinm34232]

Re: Sanyo DP42647-00 DP42647 No Picture, Has Backlight & Sound

Ok so is the collector is the input most likely the bottom left pin, outputs to the emitter on the right, and the top left should be base?

That's how I have it but I do not have the 16V on the emitter.

[tom66]

Re: Sanyo DP42647-00 DP42647 No Picture, Has Backlight & Sound

Well, simply outputting 16V would be the equivalent to a piece of wire, I suspect it's a crude voltage regulator, with its output about 0.7V below the base pin.

[kevinm34232]

Re: Sanyo DP42647-00 DP42647 No Picture, Has Backlight & Sound

Well the bad news is ordered a new T-Con with advice from a Sanyo tech that advised possible bad panel causing T-Con failure. Hooked up 1 ribbon from panel and new T-Con board turned on, with finger on Q303, get very hot very quick. Have a white spot on the tip of my finger shaped like Q303

First time for me seeing a panel shorting out the t-con.

[tom66]

Re: Sanyo DP42647-00 DP42647 No Picture, Has Backlight & Sound

Could be a capacitor or such on the panel board shorted but could also be a bad panel.