BenQ G2220HDA, white screen after cap replacement

[OniJon]

Hi!

I got this from a client of mine, totally dead. Nothing happened after plug-in nor pressing power, not even led.

Ok, so I changed all the caps, even the two on the VGA board and put the necessary components in place, hoorah, it's working. BenQ logo was on the screen and then it said "no signal" like it should. After this I took the powercord off, checked everything and wanted to test it with signal. After the connections, power button and bang, white screen. It stayed a bit then off then white again, black and once more white. It stays like that for 20 seconds before going to sleep mode, power led turns amber from the green it was with white screen.

Any advices? It should be bad connection or something but I've checked the cables 3 times already.

[Rtech]

Re: BenQ G2220HDA, white screen after cap replacement

Have you ensured that the cable from the Logic to the LCD panel is fitted properly ??

[OniJon]

Re: BenQ G2220HDA, white screen after cap replacement

Have you ensured that the cable from the Logic to the LCD panel is fitted properly ??

I've fitted it many goddamn times, with care. No help. Nothing happens in the screen if I twist it or anything. There was a little yellow stripe which was gone after re-seat of the cable.

And for the note. There seems to be wide stripe on the center which you can see only by looking from the top or bottom, almost at 180degr. angle. Looking straight, it's all white and does that blinking before goes to sleep.

EDIT:
Could it be possible that those cables from the long controllerboard have detached from the panel itself? It's a bitch to fix though if that's the case.

[Rtech]

Re: BenQ G2220HDA, white screen after cap replacement

Sometimes the fuse on the Board attached to the screen fails, so I would look at that,and the voltage regulators on the same board and the Logic Board.If that does not produce any hints then substitution of either the Logic board or a similar resolution screen,may be the only way to identify where the fault is.I recently had a monitor with similar symptoms and the Screen Board was faulty,and the only solution was a replacement screen.

[OniJon]

Re: BenQ G2220HDA, white screen after cap replacement

Sometimes the fuse on the Board attached to the screen fails, so I would look at that,and the voltage regulators on the same board and the Logic Board.If that does not produce any hints then substitution of either the Logic board or a similar resolution screen,may be the only way to identify where the fault is.I recently had a monitor with similar symptoms and the Screen Board was faulty,and the only solution was a replacement screen.

I only found one fuse from the screen board and it seems to be OK. There is also nothing else wrong about any of the stuff anywhere. I am this unlucky that by repairing the powerboard, screen fails on me. What a nightmare..

EDIT: now it shows BenQ logo on the screen when i press pwr button. After that it goes all white. Does this help with something? With input it gives these stripes in the middle of the screen horizontally. And I can see the menu too.

EDIT2: After some fighting, this works. Not perfectly but it works. Gives white screen sometimes, dunno why. After a little "battle" with input setting and like that, it gave picture. What the heck could cause that screwing with the white screen. It could work like 10mins or 10 secs and fades to totally white screen.

With little testing this works like a charm after a multiple white screens. Could there still be a bad part in the power section. Something broken because the bad caps?

[OniJon]

Re: BenQ G2220HDA, white screen after cap replacement

Here are photos of the two boards. What I'm trying to seek here if we assume that the panel/logic doesn't get the right voltages?
I'm not totally new at this but I'm not a pro, so please explain clearly.

[retiredcaps]

Re: BenQ G2220HDA, white screen after cap replacement

1) U5 is a voltage regulator. My sig file has instructions below on how to test it.

2) Check your soldering for cold joints.

3) Those are excellent pictures.

[retiredcaps]

Re: BenQ G2220HDA, white screen after cap replacement

With the voltage regulator readings, you want to take the 2 sets of measurements: when it is working properly and when you get the white screen.

There may be a voltage regulator on the panel board as well.

[OniJon]

Re: BenQ G2220HDA, white screen after cap replacement

1) U5 is a voltage regulator. My sig file has instructions below on how to test it.

2) Check your soldering for cold joints.

3) Those are excellent pictures.

Thank you very much for the info.

Ok, but now we'll not measure anything. Power just died on me. It went with "bzzzzzzup" and a little smell. Dunno exactly what burned, but everything is visually okay. Nothing burned or blackened.
The problem now is what died? No power led or anything anymore.

Bridge rectifier and all the other diodies read "infinite" other way and ~0.480V the other, this is okay then.
Black trafo near IEC measures:
pin 1-3 = 00.5 ohm
pin 2-4 = 00.5 ohm
pin 1-2 = 1.5 Mohm
pin 3-4 = 1.5 Mohm

[viziks]

Re: BenQ G2220HDA, white screen after cap replacement

Check out parts around Q601 0.22 Ohms R615,R612 etc as also smd components below in this area with a continuity tester and u may find cause of breakdown.

Samir

[Undead]

Re: BenQ G2220HDA, white screen after cap replacement

I am a total newbie here (as my post count will show), but on the small board, is that solder joint on C75 bad? In the pic it doesn't look quite right so you may want to check it.

[OniJon]

Re: BenQ G2220HDA, white screen after cap replacement

Check out parts around Q601 0.22 Ohms R615,R612 etc as also smd components below in this area with a continuity tester and u may find cause of breakdown.

Samir

Thanks.
R607 reads 62.9kohms and it should be 68kohm.
R605 is 10kohm.
R612 is 9.9ohm.

But with continuity test R615 beeps and reads 00.0 - 00.3 so that's burned right? Little SMD components give nice readings. Those L604 and L605 those coils beep too, should they? They have almost no resistance at all.

I am a total newbie here (as my post count will show), but on the small board, is that solder joint on C75 bad? In the pic it doesn't look quite right so you may want to check it.

I've done it several times now. The foil got somehow destroyed while taking the old cap out but it holds so I assume it's OK.

[Undead]

Re: BenQ G2220HDA, white screen after cap replacement

If the foil was destroyed then it will not work even if it is holding, it has to make a proper connection to the foil. You will either have to make a bridge to another component in the same section with a wire, or someone mentioned carefully sanding down to the foil in the same section and making a bridge to there.

[Rtech]

Re: BenQ G2220HDA, white screen after cap replacement

If R615 beeps, it is because it is so small,so it will probably be fine

[OniJon]

Re: BenQ G2220HDA, white screen after cap replacement

If the foil was destroyed then it will not work even if it is holding, it has to make a proper connection to the foil. You will either have to make a bridge to another component in the same section with a wire, or someone mentioned carefully sanding down to the foil in the same section and making a bridge to there.

More easily said than done. Dunno where I could connect it with a wire because this seems multilayerboard.

Anyway, logicboard ain't the main problem now because the power died.

[OniJon]

Re: BenQ G2220HDA, white screen after cap replacement

Any ideas what to measure next? It's funny how something burned with little whizzing/buzzing but nothing seems broken. Didn't arc or anything.

Need closer pics of something, let me now. I got good equipment to take photos, it's a good day to be a photographer.

[OniJon]

Re: BenQ G2220HDA, white screen after cap replacement

By the nose, I would say the yellow transformer on the powerboard is the burned one. I put an ESD pack from motherboard between the metallic panel casing and the board so I could test out the regulator. Then it zipped, could it be the transformer only because the high voltage, it jumped even with through the plastic. Should've used cardboard, damn.

[OniJon]

Re: BenQ G2220HDA, white screen after cap replacement

Updates on this, can't edit older post.

I'm getting ~320V on the main cap.
No AC or DC on the fuse, but it's fine otherwise.
around 190 volts K3530 and a exploded R615 with a nice arc. Must have shorted the K3530 legs by accident. I'm doing more damage than repairing this unit, hehe.

All in all, pretty sure K3530 is done and R615 also. Two legs on the T601 have burnings too. I'm almost done with this shit, maybe I'll just throw it to garbage and sell the panel which is fine. I'm more of a "prevention" kind of guy than repairman. I'll change the caps before anything dies, not too fond of this measuring this and that because I don't know what the heck I'm doing.

[the_raver514]

Re: BenQ G2220HDA, white screen after cap replacement

hi sir. can you give me the pin-out of the connector from the power supply to the t-con, on the t-con side if you can

[budm]

Re: BenQ G2220HDA, white screen after cap replacement

What is the model number of the LCD panel? You can look up the spec sheet of the LCD panel, it will give you the pinout.