LCD 19" BENQ T905 problems

[selldoor]

Re: LCD 19" BENQ T905 problems

@active- Main suggestion would be to read this thread from beginning to end.
You will uncover the main problems. Start with easy things check the power cord and and fuse in plug (if you have fused plugs in Greece) check the cap you replaced.
Check the fuse/s on the board. Check the transistors. When you have done that come back and advise what you have found.

[^Active^]

Re: LCD 19" BENQ T905 problems

Hi I had the same problem so i decided to change one of the capacitors that was faulty. The monitor powered up normaly and i let it run for about an hour for a test. When i decided to shut it down by the power button it wasnt responding so i pulled out the power cord and now when i plug in the power the monitor doesnt work at all .. no green light no nothing . Any suggestions?

[enoteco]

Re: LCD 19" BENQ T905 problems

Hi,
standard problem screen switch of after few sec,
following hints at post #21 and replacing C5707+9024n + picofuse;
now my my monitor work like a sharm .

Thank you all.

[dantetrade]

Re: LCD 19" BENQ T905 problems

Hi, I got the same problem, my screen lit up for a few sec and went black. I followed the instructions: desolved/resolved transformers, K's,... Bought package on ebay (5.5£) of 4transistors C5707 + 2 Fets 9024n. Replaced these and ... screen works like new. My thanks to you all.
Important !!! Use the original transistors Sanyo 400 HFE. Replacements give only 200 HFE and just last for a sec.

[jannu47]

Re: LCD 19" BENQ T905 problems

Thanx Alexanna for a quick response! Yeap, it was that! Picofuse has blown for first time and when i replaced it, the original fault came back.. A quick second or two benQ flash and then all black.. So it seems, that somehow the C5707´s burned again? Maybe those 9024N´s got to something to do with it? (I ask couple on resellers, but they don´t have them...) So i decided to use old ones... Well, they work (at once at least), because i got the picture once, only with new C5707´s...

[alexanna]

Re: LCD 19" BENQ T905 problems

Check and see if the pico fuse has gone open

[jannu47]

Re: LCD 19" BENQ T905 problems

Okay, has anyone following problem: First, the benQ logo shows about second or two, then blinks and, then shuts down the hole monitor. Fine, i have read all the messages on here, so i decided to replace the "bad" elite caps, all C5707´s, where half are burned, picofuse and re-solder all transformers.. And test.. Voila! We got a picture! :-) Also i read someone has got the picture, but about minute or two... So i decided to surf via net, use some youtube etc.. About one hour.. And we got the picture. So i assume that problem was fixed? Then i press the power button on the monitor and shut it down. Now, nothing came up, when i press pwr button.. Not even BenQ logo.. powerled stays green hole time, but no picture... Any quess, what goes wrong?

PS. Sorry about my bad english, hope that somebody can get a clue of this :-)

[chriz74]

Re: LCD 19" BENQ T905 problems

.. well the NCP 1200ap40 is gone. It reads 300V on pin 8. Does anyone have a working one? It doesn't seem that easy to find.

[chriz74]

Re: LCD 19" BENQ T905 problems

update:

I replaced all 5707 (4), 9024n (2) and the fuses. Lamps are still not working, led goes from orange to green when signal arrives from pc. I still can't see the BENQ logo.

[icewolfca]

Re: LCD 19" BENQ T905 problems

"2 seconds to black" is described in post #13 and #14 at

https://www.badcaps.net/forum/showthread.php?t=10419

Focus on

1) bad caps
2) bad inverter transformer
3) bad ccfl and/or wiring

Also, please post pictures of your boards as described in misc suggestions #1 in the same URL above.

PS. You MUST resolder all the inverter transformer pins on Benq boards.

PPS. Did you recheck the transistors to make sure they are not shorted after you installed them?

1) I replaced most caps. After reading your post I replaced more caps. I need order some more.
2) I resolder the inverter transformers prior to posting here.
3) I sure hope not

but I did check my soldering job and there was a short or two and I fixed those. It now stays on and there are no issues any more. So it is all good . I am just starting and i lack proper tools. But I am getting there. Thank you for the quick reply and I LOVE this forum.

Josh

[retiredcaps]

Re: LCD 19" BENQ T905 problems

What would cause it to work and then stop?

"2 seconds to black" is described in post #13 and #14 at

https://www.badcaps.net/forum/showthread.php?t=10419

Focus on

1) bad caps
2) bad inverter transformer
3) bad ccfl and/or wiring

Also, please post pictures of your boards as described in misc suggestions #1 in the same URL above.

PS. You MUST resolder all the inverter transformer pins on Benq boards.

PPS. Did you recheck the transistors to make sure they are not shorted after you installed them?

[icewolfca]

Re: LCD 19" BENQ T905 problems

I replaced the transistors and most caps. It now powers on and shows windows for about 1 second and then goes blank. What would cause it to work and then stop? Thank you.

[chriz74]

Re: LCD 19" BENQ T905 problems

If the power LED is green or yellow, the power supply and logic card are likely to be working. That is, 1200AP40 is working.

Yes, led is alright but BENQ logo is not showing.

[retiredcaps]

Re: LCD 19" BENQ T905 problems

BTW I can't see the BENQ logo anymore so I suppose the 1200AP40 is really gone.

If the power LED is green or yellow, the power supply and logic card are likely to be working. That is, 1200AP40 is working.

[chriz74]

Re: LCD 19" BENQ T905 problems

Thanks for the advices, I'll tell what turns out. BTW I can't see the BENQ logo anymore so I suppose the 1200AP40 is really gone. Oh I got the schematics from BENQ, I think it could be useful for future reference.

[PlainBill]

Re: LCD 19" BENQ T905 problems

How did you determine that this is blown???

The only part corresponding to 1200AP40 is a SMPS controller. If you can still see the Benq logo as you mentioned in post 7 the 1200AP40 is good.

Really, this is a waste of time in my opinion. It's difficult enough assisting in troubleshooting a monitor if the person doing the real work is interacting with us. If there is an intermediate party (you), communication becomes impossible.

1. Check for 5V and 12V from the power supply. If they are present:

2. Remove as much solder as possible from the transformer pins and resolder with real solder, not this lead free junk Benq inflicted on everyone.

3. Replace both 2SC5707s in a pair if either are shorted

4. Check both FU9024N, replace any that are associated with a shorted 2sc5707

5. Replace the picofuse if it is open.

PlainBill

[smason]

Re: LCD 19" BENQ T905 problems

update. I found two "2sc5707" are faulty and also the "1200AP40 CPBY 05475".
I tried to test the lamps and i get no value, is this normal?

The lamps are likely not a problem.
Can't speak for the 1200AP40, as you didn't really tell us what you measured, and how you determined.

As many have tried to tell you, this monitor has a very common failure mode.
Bad solder joints on the inverter transformers cause transistors to short, and blow pico fuses. Check ALL the 5707s, and the FETs, replace any bad ones, replace the fuse, while you're in there, recap, and then fire it up.

Of the 22 or so monitors I've repaired in the last year or so (and I'm still a newbie learning) several were this model or similar, and had this common failure.

[chriz74]

Re: LCD 19" BENQ T905 problems

Because it doesnt read 12v but 300v

[retiredcaps]

Re: LCD 19" BENQ T905 problems

What about the 1200AP40 BLOWN, how does that sound to you?

How did you determine that this is blown???

[chriz74]

Re: LCD 19" BENQ T905 problems

It was really a relative of mine so I don't know what kind of tester he used. I'll ask. What about the 1200AP40 BLOWN, how does that sound to you? Is this normal fault? As a result there was no power being spread to the lamp connectors.