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Old 09-09-2010, 08:49 AM   #81
capullaco
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Default Re: LCD 19" BENQ T905 problems

Ok,so only the picofuse is blown. The transistors that blown twice are also ok, and so the FU9024

The bridge I did to one of the pins from the lifted pads seems also ok, giving continuity.

So only the picofuse is blown, luckily I bought today a 125v one. (Already replaced it, thought havent assembled the board yet)

I attached some pics.

1- The transistors and the irfus.Theyre all ok.
2- Just now I noticed this soldering with the daylight.Its more golden. I just sucked it and replaced with new tin.
3- This golden tin is from one of the pins of the TR601

And the rest is the PCB in general (you can notice my fuse pins improvisement :p)

What should I do now that I replaced the picofuse? Maybe it blown cause it was 220v instead of 125v? That wouldnt make sense,would it? Btw, it has the same amp (3A).
Or maybe the 220v protected the transistors (they arent blown) caused by something?
Attached Images
File Type: jpg 1.jpg (419.6 KB, 70 views)
File Type: jpg 2.jpg (260.2 KB, 57 views)
File Type: jpg 3.jpg (483.4 KB, 63 views)
File Type: jpg 4.jpg (406.8 KB, 82 views)
File Type: jpg 5.jpg (276.0 KB, 61 views)
File Type: jpg 6.jpg (339.3 KB, 56 views)
File Type: jpg 7.jpg (341.9 KB, 71 views)

Last edited by capullaco; 09-09-2010 at 08:53 AM..
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Old 09-09-2010, 09:03 AM   #82
retiredcaps
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by capullaco View Post
What should I do now that I replaced the picofuse?
Put it away for a day. Take another look at it tomorrow when there is good sunlight and recheck the soldering.

If it looks good and transistors and fets are not shorted, try it again.
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Old 09-09-2010, 09:27 AM   #83
retiredcaps
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Default Re: LCD 19" BENQ T905 problems

Just noticed that for your jumper wire, it is not insulated. I normally see insulated wire, not bare wire.

When you put the board back in, that bare wire could be touching something and causing a short?
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Old 09-09-2010, 09:34 AM   #84
capullaco
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Default Re: LCD 19" BENQ T905 problems

Yeah,it was insulated. But I got a very short cut to made it as tiny asd possible,but at the end the plastic melted and was loose.

I think it doesnt make contact.But I will replace it.
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Old 09-10-2010, 04:23 AM   #85
capullaco
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Default Re: LCD 19" BENQ T905 problems

So I replaced the jumper wire with an insulated one.

Rechecked the bridges I mentioned in posts before, and they seem fine. Sucked the tin and the points bridged were very,very near,almost touching, so I guess its ok.

Then added tin on some solders that had little (2 pins from my solders) and the rest seemed ok.

But I tried and... BenQ logo, but its a bit dark and the display was making a sound.
Turned off and on again, same BenQ logo with artifacts. Turned it off and unplugged it.

The fuse is gone, and one of the problematic transistors too. One combination of pin reading shows 7 ohms.
And both trans have low (or I think theyre low) resistance (135~ ohm) on some of their pins.

So im at the same point as the 1st time
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Old 09-10-2010, 02:47 PM   #86
retiredcaps
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by capullaco View Post
So im at the same point as the 1st time
Right now, I can't think of anything obvious.

Maybe someone else will have some suggestions.
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Old 11-01-2010, 02:22 PM   #87
Grav
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Default Re: LCD 19" BENQ T905 problems

Hello.

I'm new too. I have the first failure described in this thread:
- Power on - Led stay green
- BenQ logo stays for 500ms
- auto power off

I can reproduce the problem.

I have read numerous threads about it. I have replaced 2 bad-shape 1000uF 10v caps.

I'm now in the mood of trying the big step:
- resolder the transformers
- change the picofuse
- change the FET
- change the c5707 transistor
(post #21 strict compliance)

Do you think i should replace some caps, too, or my failure seems to be transistor-related ?

How it could work a tiny moment, then power off ? It means the backlight is ok, so could it not mean the c5707 and FETs are ok , or exactly point they are not ? The part remains a mystery for my own comprehension
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Old 11-01-2010, 04:37 PM   #88
retiredcaps
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by Grav View Post
I'm now in the mood of trying the big step:
- resolder the transformers
- change the picofuse
- change the FET
- change the c5707 transistor
(post #21 strict compliance)

Do you think i should replace some caps, too, or my failure seems to be transistor-related ?
Before changing anything, do you have a multimeter to do the tests mentioned in this thread?
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Old 11-02-2010, 06:27 AM   #89
Grav
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Default Re: LCD 19" BENQ T905 problems

Hi retiredcaps,

I have a low cost multimeter i bought at least 15 years ago. 2 calibers (2000kohm, 200ohms with 2 digits), max 200 V DC so i can't even check the transformer output.

I plan to replace the picofuse in all ways, because i guess i'd not be able to precisely measure its state.

I 'd really appreciate an oscilloscope, but i clearly can't afford
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Old 11-02-2010, 11:06 AM   #90
retiredcaps
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by Grav View Post
I have a low cost multimeter i bought at least 15 years ago. 2 calibers (2000kohm, 200ohms with 2 digits), max 200 V DC so i can't even check the transformer output.
All you need to test the 1 picofuse, 4 c5707 transistors, and 2 fn9024 fets is the 200 ohm scale. Test the transistors and fets to see if they are shorted (i.e. less than 20 ohms). It should take about 5 minutes to test these 7 components.

On Benq boards, it is rare to have the inverter transformer be bad. More likely, it just needs to be resoldered with new solder.

Quote:
I plan to replace the picofuse in all ways, because i guess i'd not be able to precisely measure its state.
A good fuse should measure less than 1.0 ohms. You don't need anything more precise than that.
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Old 11-02-2010, 02:46 PM   #91
Grav
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Default Re: LCD 19" BENQ T905 problems

Thank you retiredcaps, this is exactly i was aiming to do.

Just to confirm, i have to unsold c5707, 9024 and picofuse to test them; i have to simply check if they are not shorted in anyway (except the picofuse which must be short).

Thank you for your advices !
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Old 11-02-2010, 03:35 PM   #92
retiredcaps
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by Grav View Post
Just to confirm, i have to unsold c5707, 9024 and picofuse to test them; i have to simply check if they are not shorted in anyway (except the picofuse which must be short).
You can test everything "in circuit". If the components test bad "in circuit" then unsolder them and retest them "out of circuit".
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Old 11-03-2010, 09:11 AM   #93
Grav
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Default Re: LCD 19" BENQ T905 problems

ok.

My bad: the caliber is 2000 ohms. No decimal display, the lowest number i can get is 0001 - if we except 0000.

For a set of transistor, i have 1 ohm on each B/C/E junctions.
For the other set, i have around 660 ohms for BC/CE/BE/CB junctions, 900 ohms for EB, and 100 ohms for EC. I assume they are ok

For the picofuse, 1 ohm, same as failed transistors. I think this is the rounding.

For 9024, i have junctions BCE going from 800 to 1200 ohms base values, always increasing (i assume they are corrects and coupled in some way with a capacitor).

I unsoldered the polyester caps, inductances, the transformers, and reflow them. grrr... one track half removed on a transformer leg, but it seems ok (i have 40w iron). I quickly resolder the c5707 to see if i have identical troubles - display for 1s then shutdown - so assuming the transformers are powering the neons and are not badly soldered.

Bought on ebay a set of 4x C5707 2x 9024 1x picofuse for 4 bucks. Next time for the real repairing

(btw, i have not replaced the caps except the bad shape - slightly growth - 1000uF / 10v)

Last edited by Grav; 11-03-2010 at 09:33 AM.. Reason: typo
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Old 11-03-2010, 10:36 AM   #94
retiredcaps
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by Grav View Post
For a set of transistor, i have 1 ohm on each B/C/E junctions.
For the other set, i have around 660 ohms for BC/CE/BE/CB junctions, 900 ohms for EB, and 100 ohms for EC. I assume they are ok
For the first set of transistor, 1 ohm indicates that it is shorted. Unsolder that set and retest out of circuit to verify.

The other set with 660, 900, and 100 ohms looks okay.

Quote:
For the picofuse, 1 ohm, same as failed transistors. I think this is the rounding.
The picofuse is good.

Quote:
For 9024, i have junctions BCE going from 800 to 1200 ohms base values, always increasing (i assume they are corrects and coupled in some way with a capacitor).
The 9024 readings look good.

Quote:
Bought on ebay a set of 4x C5707 2x 9024 1x picofuse for 4 bucks. Next time for the real repairing

(btw, i have not replaced the caps except the bad shape - slightly growth - 1000uF / 10v)
4 bucks is reasonable for a kit.
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Old 11-03-2010, 12:10 PM   #95
Grav
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Default Re: LCD 19" BENQ T905 problems

exactly 4.55$, with shipping. First i tryed to order the components at Farnells, a French (worldwide ? idk) reseller. But at the end, it was up with too much for a 'tutorial' repair:

2€ per c5707 so 4€ total
3A fuses per 10 only for 5.5€ total
2€ par 9024 - wasn't planning to buy one, but it can help -
4 € for various caps (was interested in replacing all elite's)
and 12€ of shipping...

With the Chinese eBay provider 's set, i can afford a not working c5707 in the kit, and even burn one or two more. I could wait to reach a local store for caps. Oh, i guess i'll not be shipped before next week, but this is not a problem.

Thank you for your excellent advices, Retiredcaps.

Last edited by Grav; 11-03-2010 at 12:10 PM.. Reason: precisions
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Old 11-07-2010, 12:52 AM   #96
LRN
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Default Re: LCD 19" BENQ T905 problems

Does anyone know if the 3A pico fuse at PF801 is fast acting or slow blow?

My board has STD10PF06-1 parts in the place of the IRFU9024 parts at Q805 and Q812. The difference appears to be 10A continuous drain current as opposed to the 11A for the IRFU9024.
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Old 11-07-2010, 10:23 AM   #97
retiredcaps
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by LRN View Post
Does anyone know if the 3A pico fuse at PF801 is fast acting or slow blow?
I believe fast blow based on these posts ...

http://www.badcaps.net/forum/showthr...benq+fast+blow

http://www.badcaps.net/forum/showthr...blow#post49446
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Old 11-29-2010, 04:43 PM   #98
Grav
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Default Re: LCD 19" BENQ T905 problems

So, for the end of the story:

The soldering iron heat detached a new track for the board when i changed 1000uF caps. I had to wrap a wire.

Only the 5707 were burnt. After the soldering of transformers & various elements, the lcd is working very well.

Thank you both !
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Old 11-29-2010, 04:57 PM   #99
retiredcaps
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Default Re: LCD 19" BENQ T905 problems

Quote:
Originally Posted by Grav View Post
Only the 5707 were burnt. After the soldering of transformers & various elements, the lcd is working very well.
Glad to hear it is working. The resoldering of the components mentioned earlier seems to be the key to keeping these monitors working.
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Old 01-03-2011, 01:26 AM   #100
tabbiati
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Default Re: LCD 19" BENQ T905 problems

Regards to all,
I'm new in this debate but I have the same problems already described for this monitor.
Thanks to your question I found the capacitor C824 signed with a bad weld
redone that has not solved the problem but after further tests I found that the two transistors
next to it are damaged (probably due to the welding missing).
I bought on EBay and just reach those components hope to be able to report that the monitor
is "alive again."
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