Wiewsonic VE710b black screen Flashing

[rogebe]

Hello,

I am a french guy thus not very comfortable with the language.

I have four screens wiewsonic VE710b with the same trouble.

Black screen and flashing. Flashes are regular and constant when I start

I have open. No bad caps.

But two transitors are bads (short circuit) : C5706 (see the attachement).

I replace the both and the cap associate in unsoldering on another screen

The screen is ok for 30 seconds. I see the logo "no cable" but after black screen and flashing. The same trouble.

The two transitors are again bads.

If you have an idea to solution my trouble, do not hesitate.

Good weekend.

RGB

[Rtech]

Re: Wiewsonic VE710b black screen Flashing

These usually fail on BenQ type Boards, due to Dry joints on the inverter tranformer associated with the pair that keep failing..suggest you resolder the transformer before replacing them again.

[rogebe]

Re: Wiewsonic VE710b black screen Flashing

Hello and thank you for your answer.

I have difficulty in believing that the problem results simply from a defect of dry joints.

Why? (I try to explain) :

The defaut is the same on two boards (who comes from two different screens) and at the same place.

I try to mesure connections directely on the transformer (the pins which are on transformers) with differents liaisons on the board. It's ok.

I already burned out two transistors by making a first try. I would like to be on before redoing a try.

I have somme questions :

Can I make a try without connecting the bad part ?

How to measure transformers ?

How to measure tubes if that it's possible?

Thank's for you answer.

Have a nice day.

RGB

[Rtech]

Re: Wiewsonic VE710b black screen Flashing

Well, how about some good close up photos of the bottom of the board.And bieleve me,dry joints on transformers associated with these transistors to cause them to fail, and you cannot really measure the transformers, without the proper test equipment, except for comparing the secondary resistance if the inverter transformers.

[rogebe]

Re: Wiewsonic VE710b black screen Flashing

Hello Rtech,

I make some close up photos.

It's difficult to do not be fuzzy

First the board one. I have 4 screens wiesonic VE710b and I openned 2.

One to take parts and repair the other.

I do not know if it will be sufficient to make you an opinion ?

Thanak's for you answer.

RGB

[rogebe]

Re: Wiewsonic VE710b black screen Flashing

And the second board

RGB

[Rtech]

Re: Wiewsonic VE710b black screen Flashing

Unfortunately, they need to be taken directly from above,and with a wider view.

[rogebe]

Re: Wiewsonic VE710b black screen Flashing

Oh excuse me.

I don't understand that you want.

And this ?

RGB

[Rtech]

Re: Wiewsonic VE710b black screen Flashing

That is excellent, same on the bottom will be very good.

[rogebe]

Re: Wiewsonic VE710b black screen Flashing

Ok

It's good ?

RGB

[Rtech]

Re: Wiewsonic VE710b black screen Flashing

Good photos, but difficult to tell.On the board that has the transistors missing D108 looks like that has been getting hot compared to the one on the other board.Also I would compare on each board L2,L3,D4 and D12,make sure the each measure the same and the solder on the L2 and L3 is good.

[rogebe]

Re: Wiewsonic VE710b black screen Flashing

Hello,

I test L2 and L3. All are 3 ohms.

I test D4 and D12. It's ok for the 4.

D108 is à high voltage power rectifier. It's impossible to verify without unsolder.

That you think, it is necessary to verify ?

It could not be a bad transformer or CCFL ?

Good evening

RGB

[rogebe]

Re: Wiewsonic VE710b black screen Flashing

What do you think of that ?

RGB

[rogebe]

Re: Wiewsonic VE710b black screen Flashing

I have a ccfl which comes from a bad screen (a vE710b) !

RGB

[Rtech]

Re: Wiewsonic VE710b black screen Flashing

The BRown stuff on the board is probably nothing.With the CCFL,then you can test your lamps.Just disconnect the Top Screen Lamp that is in now, and replace it with the test one,You do not have to open the screen ,just leave the test one hanging loose,leave the normal Bottom CCFL plugged in.If the fault is the same then try replacing the Bottom one with the test CCFL, leaving the normal Top CCFL plugged into its normal socket.

[rogebe]

Re: Wiewsonic VE710b black screen Flashing

Hello,

It's that possible to measure the CCFL to verify that it works ?

If I understood well. You ask me to try on an exit then on the other one.

I think that I can try on the exit that transistors burn out.

Finally I have a last question. Can i try the CCFL on a bigger screen. I have one with the power is OK. Like that I can test it.

Can I connect the power with one CCFL ? It is going to destroy the circuit ?

Thank's for your answers.

RGB

[Rtech]

Re: Wiewsonic VE710b black screen Flashing

Both sets of CCFLs must be fitted to test,otherwise it will switch off anyway.You should be able to test this one on the bigger screen.The CCFLs will NOT cause the transistors to burn out.

[rogebe]

Re: Wiewsonic VE710b black screen Flashing

Hello,

Excuse me for this silence I had some problems of connection.

But I admit that I am lost. I do not know that I do.

I try to think about a method of test to solve my problem.

Thank's for all informations that you give me but if you have any suggestions you can give please let me know.

Nice week end.

RGB

[rogebe]

Re: Wiewsonic VE710b black screen Flashing

Hello everybody

I do not know really any more how to solve my problem.

Somebody would have an idea ?

Thank you for your answers.

RGB

[budm]

Re: Wiewsonic VE710b black screen Flashing

OK, just to be sure, the brown stuff on C3 is not from the cap, take it out and look on the bottom side of that cap. Check the value of the yellow cap sitting between the two inverter transistors and make sure they show 0.22uF.