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Old 08-26-2010, 09:32 PM   #41
capullaco
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Default Re: LCD 19" BENQ T905 problems

In pairs? What do you mean? The others seem ok,which other should I replace?
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Old 08-26-2010, 09:45 PM   #42
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Default Re: LCD 19" BENQ T905 problems

The diodes are ok

Really,thanks a lot retiredcaps,not only youre helping me,but im learning a lot.
Again,thanks.
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Old 08-27-2010, 10:36 PM   #43
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Default Re: LCD 19" BENQ T905 problems

Ok,found another blown transistor.
I have marked them on the pic attached.

Between them there is a gray box called C826
Is like the 2nd pic attached.

It has a "K" on top, and on one of the sides reads:

R75 MP
.22 160
T2 05MLK13

What type of capacitator is? Which mesure? Is there any way to test it with the multimeter?
Attached Images
File Type: jpg blowntrans.JPG (290.5 KB, 77 views)
File Type: jpg Mini_box_type_Polyester_Film_Capacitor.jpg (1.8 KB, 47 views)

Last edited by capullaco; 08-27-2010 at 10:42 PM..
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Old 08-28-2010, 04:02 AM   #44
Rtech
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Default Re: LCD 19" BENQ T905 problems

If it looks in good order,ie. not swollen or split,then it is probably Ok,I have never seen one of these fail ....YET.Just ensure that you resolder the pins, because dy joints on these do happen regularly.
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Old 08-28-2010, 08:31 AM   #45
retiredcaps
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by capullaco View Post
Ok,found another blown transistor.
Yes, that I is what I meant by fail in pairs.

Quote:
I have marked them on the pic attached.

What type of capacitator is? Which mesure? Is there any way to test it with the multimeter?
http://en.wikipedia.org/wiki/File:Condensators.JPG

http://en.wikipedia.org/wiki/Capacitor#Capacitor_types

This picture is much better than the original. In the original, we could not see the entire board because of the angle.

That is why clear focused top down view pictures are so valuable.
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Old 08-28-2010, 10:54 PM   #46
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by Rtech View Post
If it looks in good order,ie. not swollen or split,then it is probably Ok,I have never seen one of these fail ....YET.Just ensure that you resolder the pins, because dy joints on these do happen regularly.

Shape seems OK, but it was between the 2 blown transistors, so I thought it could be blown also...
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Old 08-29-2010, 10:20 AM   #47
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Default Re: LCD 19" BENQ T905 problems

What is the value of the polyester caps?

Someone said, 220 nF 160V but I have read on another site that is 0,022 micro F.
Maybe the guy misspelled it and added a 0?

AFAIK 220nF = 0,22 micro F
On one side of the cap says " .22 160 " but is 0,22 pico? nano?
On top of the cap there is a "K".
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Old 08-29-2010, 01:12 PM   #48
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by capullaco View Post
What is the value of the polyester caps?

Someone said, 220 nF 160V but I have read on another site that is 0,022 micro F.
Maybe the guy misspelled it and added a 0?

AFAIK 220nF = 0,22 micro F
On one side of the cap says " .22 160 " but is 0,22 pico? nano?
On top of the cap there is a "K".
One quick and easy way to get the answer to this is to go to a site such as Digikey or Mouser. Look up the physical size of .22 F, 22nf and .22nF 160 volt caps. It becomes very easy to determine which is correct.

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For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.
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Old 08-30-2010, 12:59 PM   #49
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Default Re: LCD 19" BENQ T905 problems

Ok, after changing the blown transistors and fuse, and replacing all the Elite caps I tested the display.

It showed the BenQ logo!...but it just stayed for 2 secs, and it wasnt properly lighted, like if the brightness was low.
Between those 2 secs, there are some artifacts, like color inverted image,etc..

Also, the display started to stink a bit, so I disconnected it.

What can it be now?
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Old 08-30-2010, 01:09 PM   #50
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by capullaco View Post
What can it be now?
Did you resolder all the transformer pins and other components as suggested in post #21?
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Old 08-30-2010, 01:15 PM   #51
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Default Re: LCD 19" BENQ T905 problems

Err...no
Which ones are the transformers? The box like ones?
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Old 08-30-2010, 03:45 PM   #52
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by capullaco View Post
Err...no
Which ones are the transformers? The box like ones?
What retiredcaps is talking about are the 4 inverter tranformers. If you look at the first photo in post #26, they are the 4 small square yellow boxes on the left side of the photo. You should use desoldering braid to soak up the old solder from the transformer pins and then apply new solder. Do this for all 4 transformers.
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Old 08-30-2010, 04:41 PM   #53
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by jetadm123 View Post
What retiredcaps is talking about are the 4 inverter tranformers. If you look at the first photo in post #26, they are the 4 small square yellow boxes on the left side of the photo. You should use desoldering braid to soak up the old solder from the transformer pins and then apply new solder. Do this for all 4 transformers.
Ok im gonna try. But do you think those fuckers are gaving those problems? The display started to stink when I turned it on
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Old 08-31-2010, 05:30 AM   #54
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Angry Re: LCD 19" BENQ T905 problems

Ok, so I was going to resolder the transistors today,but tried the display first.

Its broken again

Guess Ill have to change the fuse and the transistors again
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Old 08-31-2010, 10:26 AM   #55
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by capullaco View Post
Guess Ill have to change the fuse and the transistors again
Read post #21. Look at the very last sentence.
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Old 09-02-2010, 08:45 PM   #56
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Default Re: LCD 19" BENQ T905 problems

Ok, my mobile is working again.

Took photos of 'problematic' bits:

Code:
Photo number. Description
1. Those are the transistors that were originally blown.Theyre blow again (the left arrow actually indicates the trans,not the cap :p)

2.The bottomside of those transistors.Those 2 yellow points,are bridged (they have continuity and the polimeter beeps with the diode/continuity beep setting).
Im not sure if they should be bridged... One is a pin of the 'K' cap of the 1st pic and the other one is a SMD named "JR10"

3.Those are another bridged point.The cap pin is bridged with a drop of tin that it was already on the board.I think its ok

4.I tried to compare those bridged with the image posted here, but im not sure, so I marked them

5.Two new blown transistors.I dont know if they were blow before, but theyre now.They have a heatsink and theyre glued to it.
Also, theyre special and are larger with a hole for a screw. Its one piece, I mean its not a transistor glued to another one. Wonder if I will be able to buy that type of transistor...Also, I dont know they ID, but I guess the guy in the shop will know.

6.Those are the things I have to resolder right? Are they marked correctly? What are those two things marked as '?' ? Should I resolder them also?

7.Finally, this is the bit I said it was burnt.but the transistor under it its fine.
Attached Images
File Type: jpg 1blowntransistors.jpg (202.5 KB, 100 views)
File Type: jpg 2blowntransistorspuente.jpg (295.4 KB, 99 views)
File Type: jpg 3puente2.jpg (345.8 KB, 86 views)
File Type: jpg 4BenQ PS PCB.jpg (305.6 KB, 80 views)
File Type: jpg 5newblowntrans.jpg (241.4 KB, 89 views)
File Type: jpg 6transf.jpg (314.8 KB, 113 views)
File Type: jpg 7burnt.jpg (191.2 KB, 76 views)

Last edited by capullaco; 09-02-2010 at 08:51 PM..
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Old 09-02-2010, 11:40 PM   #57
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by capullaco View Post
1. Those are the transistors that were originally blown.Theyre blow again (the left arrow actually indicates the trans,not the cap :p)
Yes, because you chose to ignore 3 people telling you 4 times to resolder the transformers. This problem with the Benqs has been known for about 2 years now. When people say you *must* resolder the transformer it is because they have experienced what you have.

We can lead a horse to water ...

Here is the technical explanation why the transistors short out.

http://www.badcaps.net/forum/showpos...&postcount=269

A poor analog might be the following (I can see PlainBill shuddering right now). Imagine a car engine as the transformer. When the bolts holding down the engine are loose, it shakes all the components of car.

You take the car to the mechanic (Eric the car guy). Eric says I can fix the loose radio, loose hoses, loose steering wheel, etc from all the damaged caused by the engine for $500.

Eric also HIGHLY recommends that he rebolts and remounts the engine. It will cost $1000. You balk. 2 days later, the engine causes the same damage. This time Eric charges you $1000 because the engine caused more damage than the first time.

Eric again recommends remounting and rebolting the engine, but this time it is $1500 because of more damage. You balk again.

And so on ...

Quote:
2.
Im not sure if they should be bridged... One is a pin of the 'K' cap of the 1st pic and the other one is a SMD named "JR10"
If you follow the circuit green pcb trace you should be able to tell if they are on the same circuit path or not. If they are, then it is not a problem if they are bridged.

I started here on these forums back in April 2010, but I can't remember a single case where a bridged connection has been documented as a problem.

I asked a similar question. See

http://www.badcaps.net/forum/showthr...+solder+joints

Quote:
4.I tried to compare those bridged with the image posted here, but im not sure, so I marked them
That is a good idea, but be aware that there are possibly many revisions of this board. Manufacturers can change the boards as they see fit.

Quote:
5.Two new blown transistors.I dont know if they were blow before, but theyre now.
The picture's angle makes it hard to see, but those are probably dual diodes? They should have 2 diode symbols pointed towards the center.

What measurements did you get for these dual diodes?

Quote:
6.Those are the things I have to resolder right? Are they marked correctly? What are those two things marked as '?' ? Should I resolder them also?
Yes, resolder those. L indicate an inductor. T is a transformer.

Quote:
7.Finally, this is the bit I said it was burnt.but the transistor under it its fine.
Some browning is normal. As long as the transistor underneath tests okay, it is fine.
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Old 09-02-2010, 11:45 PM   #58
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Default Re: LCD 19" BENQ T905 problems

One other suggestion.

Once the new parts come in, check them all out of circuit to ensure they are good.

When you get all the repairs done, put away the monitor for 2 days. Come back 48 hours later with post #21 printed and go through each sentence top to bottom and bottom to top (i.e doublecheck all your work).

That will give your brain some time to process the repair.

Additionally, BEFORE you power up. Doublecheck all the components again to make sure they are soldered in properly, oriented correctly (not backwards) and retest them with your mulitmeter "in circuit".

Then and only then, apply power.
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Old 09-03-2010, 05:14 AM   #59
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Default Re: LCD 19" BENQ T905 problems

Thanks again retiredcaps.

If I didnt resolder the transformers, its because I wasnt sure which ones were them, until jetadm123 pointed them out.

That being said, I also didnt research more, because after checking that the fuse and the transistors were blown, I thought that those were all the problems the PCB had.

One thing im still not sure:

Code:
Desolder all 4 transistors and the polyester caps (between the transistors
Is the polyester cap the 'K' cap from my first pic? Theyre 2 so it makes sense, but just to be sure.

About the dual diodes, yes they are.Theyre named "DXXX" and they have this printed on one side:

YG902C2
-->|--|<-- CI
40 121

I managed to unstick them from the heatsink.
But how do I test them? I tried this but I dont know if its correct:

- Black (COM) on 2nd pin RED on 3rd: 400
- RED on 1st pin BLACK on 2nd: 400

Those values are with the diode setting ( -->|) of the polimeter. Other combinations didnt show results.

The things I need to resolder, I just need to unsolder them and sold again with new tin or is there any other action involved? I ask because the soldering on those things seems ok , at least on looks.
One more thing, should I resolder those things marked as '?' on the 6th pic?

Last edited by capullaco; 09-03-2010 at 05:23 AM..
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Old 09-03-2010, 06:11 AM   #60
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by retiredcaps View Post
Yes, because you chose to ignore 3 people telling you 4 times to resolder the transformers. This problem with the Benqs has been known for about 2 years now. When people say you *must* resolder the transformer it is because they have experienced what you have.

We can lead a horse to water ...

A poor analog might be the following (I can see PlainBill shuddering right now). Imagine a car engine as the transformer. When the bolts holding down the engine are loose, it shakes all the components of car.

You take the car to the mechanic (Eric the car guy). Eric says I can fix the loose radio, loose hoses, loose steering wheel, etc from all the damaged caused by the engine for $500.

Eric also HIGHLY recommends that he rebolts and remounts the engine. It will cost $1000. You balk. 2 days later, the engine causes the same damage. This time Eric charges you $1000 because the engine caused more damage than the first time.

Eric again recommends remounting and rebolting the engine, but this time it is $1500 because of more damage. You balk again.

And so on ...
Actually, that is an excellent analogy. You teach well, Grasshopper!!

PlainBill
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