Fix for Benq FP737s 17" (Q7T3)

[EGuevarae]

Originally Posted by vicrowley

Hi Dave,
I have recently been given one of these Benq 17” monitors, but only because it had died. I’m only an amateur dabbler in electronics, and I think I’ve just about been able to follow most of your circuit mods, and the reasoning behind them. Now I know from the dates on the posted articles, it was some time ago you were working on this monitor, but I was wondering if you now have a final definitive modification list, and final circuit diagrams. I ask this as reading through the various posts, you were obviously developing and changing things as you found new problems, and from reading through, it is hard to be sure I’m using your final solution for all the mods.

PS. I hope I’ve entered this in the right place, I’m new to this forum.

Vic

Welcome to the forums.
While the post is in the right place, you might want to PM davmax directly.

[vicrowley]

Thanks, will look and see how to do that.

Vic

[davmax]

In response to a request for the final modification details
I have made this easy by posting the final versions at an online album here: http://picasaweb.google.com.au/davmax60/MonitorRepairs#

Use the full screen facility to see the detail.

Please note that there are two versions of current sense resistor, either a single resistor or two in parallel. Therefore the photo of the board underside shows the 0.082 ohm resistor version (alternately this resistor would be 0.56 ohm). The photo of the upper board shows the position of the 0.1 ohm resistor.

[davmax]

I feel I should add that to achieve the modification I describe you will need all the tools.
A soldering iron and self fluxing solder.
A PCB drill and bit 0.8 - 1 mm
A sharp knife to cut tracks.

[vicrowley]

Thanks for the advice, and as far as the actual work of the board is concerned, I’m fairly confident on that score. In the past when I used to work for my living (now retired), I was for a few years in a data collection lab, and soldering strain gauges, some of which were only thirty thou long, and that included the two solder tags. So we had to work under a 30 to 1 microscope. I guess that’s why I now need glasses. So like say the physical stuff I can deal with, it’s the technical working of these modern electronics I know nothing about. It’s all black boxes (Chips), and unless I know what each of these does and how it achieves it, I’m lost. So thanks for doing all the hard work, and I’ll let you know once I’ve completed the task, if my confidence was well founded or not.

Vic

[Lim Yong Seng]

Hi Everybody,

Thanks all of you for the useful postings which help me to repair a BenQ FP731.
It does not have any display with the green LED stays on.

Things done
-------------
1. Replaced fuse (BEL MS 3A), PF751 is open-circuit. I used a 2A pico fuse because I do not have a 3A fuse on hand.

2. Solder inverter transistors (2SC5707), Q739, Q740, Q759 and Q760. The solder cracked when I moved these 4 transistors.

3. Solder power MOSFETs (FU9024N), Q743 and Q751. The solder cracked when I moved these 2 MOSFETs.

4. Solder transformers, T751, T752, T753 and T754. No solder cracked, just re-solder to prevent dry joints.

5. After power on, left half of the monitor displays information correctly but right half has pink background with a continuous black line in the centre of the screen.

6. Remove the two flex-cables and clean the contacts (dirt found) with alcohol.

7. Power on and the monitor is in working condition.

Once again, thanks all you for the important information.

Have a nice weekend...Yong Seng

[EGuevarae]

Originally Posted by Lim Yong Seng

Hi Everybody,

Thanks all of you for the useful postings which help me to repair a BenQ FP731.
It does not have any display with the green LED stays on.

Things done
-------------
1. Replaced fuse (BEL MS 3A), PF751 is open-circuit. I used a 2A pico fuse because I do not have a 3A fuse on hand.

2. Solder inverter transistors (2SC5707), Q739, Q740, Q759 and Q760. The solder cracked when I moved these 4 transistors.

3. Solder power MOSFETs (FU9024N), Q743 and Q751. The solder cracked when I moved these 2 MOSFETs.

4. Solder transformers, T751, T752, T753 and T754. No solder cracked, just re-solder to prevent dry joints.

5. After power on, left half of the monitor displays information correctly but right half has pink background with a continuous black line in the centre of the screen.

6. Remove the two flex-cables and clean the contacts (dirt found) with alcohol.

7. Power on and the monitor is in working condition.

Once again, thanks all you for the important information.

Have a nice weekend...Yong Seng

Congratulations, and welcome to Badcaps.Net!

[enterthehatrix]

Hey guys.

Got all my monitors working except one, which virtually burst into flames.

The good news is that the LCD and the little VGA board still work.

Has anyone else tried to manually power this up? I intend to use the screen as a light weight portable screen backlit by LEDs and powered by batteries (if possible)

Could someone try this and if it works, could they do a diagram of the VGA board and point out which pins require what voltages, etc?

On the schematic, it has BLT_ON and BOLT_ADJ which I assume is the backlight, PW_DOWN (no idea), Volume On/off and volume (not used), GND, P12V, P3.3v, +3.3v, and +5v

What's the difference between P3.3v and +3.3v?

[Caloute]

Hi all,

Go the parts from ebay (Actually bought 2 sets), replaced all 7 parts.
Before it was completely dead, now with the new parts, it actually shows benq logo, or destop image, but just for 2 seconds and then nothing. Any idea?

I kind of gave up, so if anybody from Australia is interested in buying the parts, or the screen for further part such as casing etc...I suppose the screen is still good...
Anyways let me know.

[EGuevarae]

Originally Posted by Caloute

Hi all,

Go the parts from ebay (Actually bought 2 sets), replaced all 7 parts.
Before it was completely dead, now with the new parts, it actually shows benq logo, or destop image, but just for 2 seconds and then nothing. Any idea?

I kind of gave up, so if anybody from Australia is interested in buying the parts, or the screen for further part such as casing etc...I suppose the screen is still good...
Anyways let me know.

Resolder the transformers and other common solder points (see all the thread). You'll be fine.

[fety]

LOOK people! 9 times out of 10, Cold solder joints DO exist on the board. Looky what I found on mine! BE SURE TO REMELT OR (better yet) RESOLDER THE TRANSFORMERS!!!

btw, this is from a Dell E172FP / E172FPb

[fety]

Well CRAP!! It didn't work! I got the kit on ebay and replaced all 7 parts and resoldered the transformers as well as resoldered a few other suspiciously lame looking solder joints. Nothing shows up on the screen now, just the power LED blinks about every 1.5 seconds AND I can hear a faint tick sound. Like what HelpQuick experienced... What is this a symptom of? what can I try next? replace all/most of the caps? Btw, I'm not an electrical guru, I just have a A. W. Sperry AMM to work with so don't ask me to test this or that if I'm not capable of doing so. Thanks

HEEEEELLLLLLLLP!!!!!!!!

[PlainBill]

Originally Posted by fety

Well CRAP!! It didn't work! I got the kit on ebay and replaced all 7 parts and resoldered the transformers as well as resoldered a few other suspiciously lame looking solder joints. Nothing shows up on the screen now, just the power LED blinks about every 1.5 seconds AND I can hear a faint tick sound. Like what HelpQuick experienced... What is this a symptom of? what can I try next? replace all/most of the caps? Btw, I'm not an electrical guru, I just have a A. W. Sperry AMM to work with so don't ask me to test this or that if I'm not capable of doing so. Thanks

HEEEEELLLLLLLLP!!!!!!!!

That ticking sound is a symptom of the power supply shutting down and restarting. Have you checked the transistors you installed?

PlainBill

[fety]

Originally Posted by PlainBill

That ticking sound is a symptom of the power supply shutting down and restarting. Have you checked the transistors you installed?

PlainBill

Check them, how? they're brand new...from the 7 piece kit on eBay. Would they fry instantly? Solder looks good.

[PlainBill]

Originally Posted by fety

Check them, how? they're brand new...from the 7 piece kit on eBay. Would they fry instantly? Solder looks good.

Use an ohmmeter.

Yes, they can short instantly if the problem that caused them to short is still present.

PlainBill

[steven.va]

Hi All,

I got a Benq 17" Q7T3 TFT like you all.
It had it's two 2SC5707 shorted, FU 9024n shorted, 3A fuse open.

So far I have replaced the fet with an IRF9540, wich according to
my suppier is a good replacement.

I replaced the two broken 2SC5707's with TIP132. I know this is not good, however it was the only thing I could get my hands on...
Resoldered the transformers, resoldered other suspicious joints too.

Powering the TFT up:
Well: it did not go up in smoke

Backlight works, and it shows the "Benq" logo. Went out after 4 seconds.
I Tried that again:
So I connected a PC and it showed the window desktop just fine, but again, the monitor shutted itself down after a few seconds (faster every time)

Things tried with data cable disconnected:
- Connected CCFL lamps to inverter 1 (the good one)
---> Screen is lit, shuts down after a few seconds
- Connected CCFL lamps to inverter 2 (the repaired one)
---> Screen is lit, shuts down after a few seconds
- Connected CCFL lamps to inverter 1 & 2
---> Screen is lit, shuts down after a few seconds

However: when feeling at the TIP 132 transistors they get HOT.
I can barley touch them with my hands.

....while the two remaining 2SC5707 are actually cool running.
Is the TFT shutting down because of the improper transistors used, or is there another fault I can check that overheats the TIP 132's

Should I swap the two remaining good 2SC5707 with TIP132 too just to see that they overheat too or not?

Greetings and thank you in advance!
S.

[Bobdee]

You need to go with 4 of the 2SC5707s or 4 of others, but the TIPs are known to run hot (not recomended)

[steven.va]

Originally Posted by Bobdee

You need to go with 4 of the 2SC5707s or 4 of others, but the TIPs are known to run hot (not recomended)

Could that explain the shutting down of the inverter after 4-5 seconds?

Greetings,
S.

[Bobdee]

Yes in one
You need to go 4 of same type
Easy and quick to get 2SC5707s on ebay

[steven.va]

My 2SC5707s arrived. Soldered them in, and my Benq FP731 works!

I did resolder the connections to transformers.

Greetings,
Steven