770 bad inverter.....why?

[solidpro]

Hi All

I'm working on a 770. The display is totally dark (but you can see an image if you shine a torch). I don't know for certain if it's the CCFL tubes or it's the inverter.

I've measured voltages across the inverter and it all seems to go dead about halfway across. Here is a pic of it https://ibb.co/hdMtK14

Replacements are extremely hard to come by. The inverter has no electrolytic caps on it at all - just, it appears 1 unmarked tantalum cap at C3 (which I thought was a fuse but if you measure ohms across the two pins it counts up for ages).

If I measure AC across the 2 pin output to the LCD's CCFL tubes I get nothing at all....

Any ideas!?

Thanks

[RealBlackStuff]

Check the Fuse F1 for continuity (near the top of that picture).
If you can see some vague image, then the backlight is obviously not working.
Don't know if there is a backlight fuse on the motherboard.
Do you see a picture on an external monitor?

[solidpro]

Well spotted. F1 was blown. I've temporarily bypassed it and now the screen powers on but constantly flashes. About twice a second. Constant.

External monitor is fine.

Any ideas about the flashing?!

Thanks

[RealBlackStuff]

When powered off, move that slider on the inverter a couple of times up/down, it may have some corroded contacts.
Also check/refresh the solder connections of that round thingie (inductor?).
T2x series used to have many problems with those due to bad soldering.

[solidpro]

I've been meaning to try this but I've been spending the last 2 days tiling a bathroom.... I'll check on it shortly and report back! Thanks!

[solidpro]

No go, I'm afraid.

I re-soldered the inductor and de-oxed the slider giving it lots of wiggle. Still the same. I've seen this before - maybe it's a failing CCFL (if there is only 1....)

I managed to source another good lid with LCD and that has gone in it's place.

Best Wishes

Alex

[Oelmuvun]

There is indeed only one CCFL tube running across the bottom of the panel, at least in my 13".

Since you already replaced the offending lid, if you still have the inverter and panel it is possible to add a LED backlight as a last ditch effort to save the parts from an e-waste pile.
I very recently did my 13" with a random LED backlight kit from the internet non-destructively. Personally I really don't see ever putting a CCFL tube back in, and my lid is on the mangled side of things anyway as this is a project sort of machine.
All of the needed connections are right in the same spot, and the brightness slider still works. I did also slightly trim the backside of one of the panel brackets to pass the wires under, and had to extend the backlight wires to reach the side they originally fed into. The LED strip was trimmed to length and tacked down in a couple spots with a bit of glue that I could scrape off if I really had to.
On this particular generic kit the red is VCC, yellow is enable, black is ground, and white is brightness 0v=full to 5v=dim. The brightness slider provides 0-5v and 5-0v depending what of the pins you tie into.
Here is a thumbnail:

I have not seen the inside of a 14", but I presume there is not as much space and one would either have to shorten the original inverter board or mount the new board remotely and run the wires along one of the hinges.
There does not look like enough space to mount the new board behind or in front of the inverter or behind the panel.
Your mileage may vary.

[solidpro]

Hi

I've tried a few CCFL-LED swaps on LCDs and they always end up awful. I can never get enough diffusion from the LED strip to have a continuous white light along the side (like a CCFL does naturally). I even tried ready made 'kits' from Asia but they were equally as bad. Not sure what I'm missing...

The faulty lid has gone into my parts bin as a useful lid and inverter but dodgy LCD...

Regards

[Luizapper]

Hello,

I've recently tried out a LED swap on a 13.3" LCD panel of a 770 and it has proven to be good backlight solution (at least for me), it only gets little dim at both ends because LED strip length being 3mm less than it should be, if it were next size bigger it involved more modification (and risk of damage) of LCD bezel.
It's white color temperature is slightly more cool than original CCFL (comparing to a new tube), but it's not too blueish.
Here is a photo of the result (ignore error message):



The LED strip solution used was bought from Aliexpress. It has 275mm in length and being a pack of 2 LED strips now I have spare one




The LED strip is totally installable where the CCFL tube is, just by slightly lifting the panel from the metal frame and sliding into the reflective tube, maintaining their both end rubbers and central o-ring spacer.
It needs just a little cut (with a knife) along the rubber ending where the new led strip wires comes out just to embrace them.
Then both wires takes the same path of the original short wire and connects to it's driver, which is totally installable between panel cover and left side of the LCD panel and hinge.

[solidpro]

Couple of novice questions:

1) Got a link to the exact aliexpress item?
2) Was the driver included?
3) Does the driver have to be wired into the existing inverter feed (I'm assuming it cannot come from the HV inverter +/-
4) (how) Does all this extra circuitry fit inside the lid/bezel?
5) How is diffusion? My issues replacing CCFL with LED in the past is the diffusion was terrible, leading to light/dark ladder across the top of the screen.

[Luizapper]

Couple of novice questions:

1) Got a link to the exact aliexpress item?
2) Was the driver included?
3) Does the driver have to be wired into the existing inverter feed (I'm assuming it cannot come from the HV inverter +/-
4) (how) Does all this extra circuitry fit inside the lid/bezel?
5) How is diffusion? My issues replacing CCFL with LED in the past is the diffusion was terrible, leading to light/dark ladder across the top of the screen.

1) Yes, you can click on the item's image above or check this other post link.
2) Yes
3) Yes, check this other post link to know how to.
4) Fits in 770's display case on left side of the hinge, mainly if there is a 13.3" panel.
5) I was also afraid of that poor light diffusion, but in this LED kit turns out to be good enough, just little dim on the both ends.

This is a "worst case" scenario when using a fullscreen white image in lowest brightness:

Also to consider that taking a photo is worse than seen by our eyes.

[el_Capo]

This is a "worst case" scenario when using a fullscreen white image in lowest brightness:

Also to consider that taking a photo is worse than seen by our eyes.

very nice result!!i I want to do the same in my 770X ... the LED backlight is dead ...

[Luizapper]

This is a "worst case" scenario when using a fullscreen white image in lowest brightness:

Also to consider that taking a photo is worse than seen by our eyes.

very nice result!!i I want to do the same in my 770X ... the LED backlight is dead ...

Thanks! Be sure about the led strip length to choose from.
I once had a 770X too with 14,1" LCD panel 1280x1024 resolution it should be slitghtly bigger in bottom, maybe about 5 mm judging from what I remember, so it could be less roomier to place the led driver.
Good luck with that mod.