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Old 03-19-2012, 04:20 PM   #41
budm
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Default Re: VX 724 black screen green light flashing

Not sure about the substitute transistors, but one reason the transistor is blown can be due to the bad tuning cap (brown cap next to the inverter transformer), one per transformer. You should take them out and measure the value and the resistance (it should show open with the meter set to highest Ohm range), if the cap is bad, you will damage your new transistors. The not working lamp transistor reading is bad, you should replace them in pair anyway.
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Last edited by budm; 03-19-2012 at 04:26 PM..
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Old 03-19-2012, 04:25 PM   #42
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Default Re: VX 724 black screen green light flashing

Yeah, I have already replaced that capacitor too, the brown one. It was a bit open (literally).
I also replaced the big cap for a new one even though it seemed to be working.

Thanks for the quick reply.
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Old 03-19-2012, 05:41 PM   #43
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Default Re: VX 724 black screen green light flashing

I have just seen that you edited your message.

Like I told you, I've already replaced the brown cap. The only thing left is to replace the 2 transistors but I can't find 2SD1628 or the similar ones (as far as I know, these ones should work too 2SD1624,2SB1124,2SC4672).

Thanks!
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Old 03-19-2012, 06:42 PM   #44
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Default Re: VX 724 black screen green light flashing

2SB1124 is PNP.

Japanese Transistors:
2SAxxx, 2SBxxx = PNP
2SCxxx, 2SDxxx = NPN

I did not look up the 2SD1624 spec to see if it has Low Vsat, and Ic, Icp (these are important spec). A little lower Vceo may be OK.
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Old 03-19-2012, 07:21 PM   #45
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Default Re: VX 724 black screen green light flashing

Great to know. I'll check Vsat, Ic, Icp, etc. Also, I'm gonna try and check the CCFL transformers.

I'll let you know if I have any news. Thanks for your input and quick replies!
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Old 03-20-2012, 02:03 PM   #46
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Default Re: VX 724 black screen green light flashing

I checked the CCFL transformers and I got same values on both of them. The transformer where the lamp works gave me the same values than the one that doesn't work.

The only thing left to think are the 2 transistors. I can buy 2SC4672, it should work, right? The Vceo is 30V less than 2SD1628 but Ic and Icp are 2A less than Ic and Icp from 2SD1628.

Thanks for your input, budm.
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Old 03-20-2012, 02:09 PM   #47
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Default Re: VX 724 black screen green light flashing

The Vsat and other spec look great but the current handling is a lot lower than original, you can try, but it may not last.
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Old 03-22-2012, 09:06 AM   #48
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Default Re: VX 724 black screen green light flashing

I'm reading the first page of this thread and someone said that the original transistor is 2SC4672, so if I replace it with 2SD1628, should it work too?

For 20 dollars I can buy a working board on eBay and that almost the price of 5 of those transistors in my country (because they've to import them).

What do you think it'd be best? Buy the transistors or a used (but working) board?
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Old 03-22-2012, 12:57 PM   #49
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Default Re: VX 724 black screen green light flashing

Quote:
Originally Posted by Nocta View Post
I'm reading the first page of this thread and someone said that the original transistor is 2SC4672, so if I replace it with 2SD1628, should it work too?

For 20 dollars I can buy a working board on eBay and that almost the price of 5 of those transistors in my country (because they've to import them).

What do you think it'd be best? Buy the transistors or a used (but working) board?
Transistors are a tricky lot and there's no guarantee that using a substitute will work. And even if they do work, there's no guarantee that there aren't other problems with the board. If the working board is just a bit more cost wise, then that may be the route to go. Since it is used, check the seller's feedback rating to see if they have been accused in the past of trying to pass off broken parts as working. Good luck!
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Old 03-22-2012, 01:01 PM   #50
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Default Re: VX 724 black screen green light flashing

I would buy used board so you will have spare transistors, transformers, caps. Make sure to inspect the caps by the inveter transformer or replace them since that will cause the transistors to fail when those caps go out.
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Old 03-22-2012, 01:58 PM   #51
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Default Re: VX 724 black screen green light flashing

I bought a used board for 23 bucks. To be honest, it's much better this way because I don't have to check everything.

@jetadm123 I checked the user and they have 99,9% positive califications. It's a pretty high number. Thanks for that detail because I'm thinking of buying another board. I got a BenQ FP767 and its board has been already manipulated and some components are missing. Instead of buying and looking at a circuit, I'll buy a new/used board too. It's easier and i'm sure it works.

Thanks guys. Even though I bought the board, I learnt a lot here and that's what I appreciate over all!

Quote:
Originally Posted by budm View Post
I would buy used board so you will have spare transistors, transformers, caps. Make sure to inspect the caps by the inveter transformer or replace them since that will cause the transistors to fail when those caps go out.
Thanks for pointing that out. I changed all the caps on the inverter/power board. I also changed (just in case) the cap close to the pins that connects the video with the inverter board and the H154 behind the transformer of the not working lamps (that one was a bit cut).

Last edited by Nocta; 03-22-2012 at 02:05 PM..
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Old 04-13-2012, 09:23 AM   #52
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Default Re: VX 724 black screen green light flashing

Ok guys, so yesterday the board arrived. I changed it and so far it's working but I have a problem and I don't know what could it be :/

I attach pictures and a video so you can see my problem. It's weird, like if I were set in 16-bit colors :/

I hope you can help me.

PS: The board has a jumper which I can set in 6,5 , 7 or 7,5mA. I didn't change it, it was set in 6,5mA. Do you think that could be the problem?

I'm starting to doubt, maybe the lamps are not working great.

http://tinypic.com/r/1z9gk4/5
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Old 04-13-2012, 10:24 AM   #53
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Default Re: VX 724 black screen green light flashing

That is the jumper to set the inverter board to drive difference CCFL bulbs current as needed for particular lamps since the same board can be used in the smaller or larger LCD panels.
I am not sure what I am seeing in your pictures.
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Basic LCD TV and Monitor troubleshooting guides.
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Inverter testing using old CFL:
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TV Factory reset codes listing:
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Old 04-13-2012, 10:59 AM   #54
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Default Re: VX 724 black screen green light flashing

So, what you think I should try set the jumper at 7mA and see what happens?

I know pictures are not clear. The problem is, for example, if I have a black square, I see it a bit grey and with green lines. Am I clearer now?

I attached new and better pics.

Thanks.
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Old 04-13-2012, 11:13 AM   #55
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Default Re: VX 724 black screen green light flashing

OK, I see the picture problem now in #2 picture.
I think you may have another problem in the Main logic board due to bad regulator or caps for the video processing. At least try reseating the Ribbon cable from the logic board to the LCD panel first. You may want to verify that you do get good 5vdc from you new board.
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Old 04-13-2012, 11:16 AM   #56
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Default Re: VX 724 black screen green light flashing

I have not really followed this thread but The new power board you bought did it look as if it had been reworked. What make /series caps does it have in?

Did you re cap the video board and again what caps did you use?

Did your old board have the jumper for the lights - if so what was that set at?
This should be set the same? having said that the problem you have doesnt really look like its related to the brightness of the ccfls.

Have you tried a factory reset.

If the your old board did not have the power jumper - have you bought the correct board?


Is the pc set at the optimum resolution for the screen

Have you done the normal power board checks on the new board - voltage on main cap and output voltages.
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Old 04-13-2012, 11:27 AM   #57
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Default Re: VX 724 black screen green light flashing

I had the "2 seconds to black" problem with my old board. The 2 seconds I had image, it was just like now but I thought it was the power/inverter board but now I realize it was not.
The old board had no jumper for the lights. The board is the same but a different model. The partnumber seems to be the same (unless it's a fake) but clearly a different model. For example, the main cap filter is 100uF and the original board had a 150uF. Plus, it has a big transformer for the 4 light connectors. The other one had 2 little transformers.
I don't know the brand of the caps on the new board. They were green.

I tried also with a VGA cable (now it's connected with a DVI cable) and I had the same result.
The PC is not the problem either because my other monitor works just fine. I connected this monitor (Viewsonic) to my laptop and same thing.

I'll try cleaning the Ribbon cable. Is it OK if I use isopropyl alcohol?

EDIT: Caps are Taicon.

Last edited by Nocta; 04-13-2012 at 12:15 PM..
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Old 04-13-2012, 12:48 PM   #58
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Default Re: VX 724 black screen green light flashing

Ok, so I cleaned the ribbon cable with isopropyl alcohol and nothing. Changed the jumper and nothing.

The caps of the power board are Taicon.
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Old 04-13-2012, 01:22 PM   #59
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Default Re: VX 724 black screen green light flashing

Ohhhh! when you said green I immediately thought Teapo or Taicon. They are usually replaced on sight. Can you post pictures of your boards.

"Changed the jumper and nothing." do you mean no change or nothing?
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Old 04-13-2012, 04:48 PM   #60
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Default Re: VX 724 black screen green light flashing

LOL. The original caps are TEAPO and the ones on the board I bought are Taicon.

I changed the jumper, means I changed its position (to 7 and 7,5mA) and still the image is not good.

I changed a couple of caps from the logic board but not all of them (yet). I'm working on that.

Thanks for your input!
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