Fix for Benq FP737s 17" (Q7T3)

[R_J]

Re: Fix for Benq FP737s 17" (Q7T3)

I just repaired a Dell E173FPb (Benq board) that had one shorted 2sc5707, and the cause was poor solder connections on components in the inverter, (transformer and cap. c735) plus other misc. poor connections.

[Behemot]

Re: Fix for Benq FP737s 17" (Q7T3)

I am just curious, did somebody found the final solution? From what I remember when I've read this through half a year ago, I remember davmax found there are some spikes when the display goes off and back on right again while restarting system (pre-POST). I also think I remember he thought he found the solution but than the 2SC5707 just blew again…

[oddbodd]

Re: Fix for Benq FP737s 17" (Q7T3)

Yes, I think that should have resoldered first and then replaced later. Lesson learnt.

I'll bear that in mind, about the caps, too. Thanks

[selldoor]

Re: Fix for Benq FP737s 17" (Q7T3)

Hi -Well done! This often happens unfortunately. The 5707s are shot and are replaced but if the soldering is not redone then they go again as it is the main reason they went bad in the first place.

To increase its life expectancy you could also replace the middle size caps
if not all except the BIG one.

[oddbodd]

Re: Fix for Benq FP737s 17" (Q7T3)

Good news. I now have a working monitor again!

I was almost ready to call it a day. After desoldering/resoldering everything suggested in the earlier post... it still didn't work.

So I retested the new C5707s and found that one pair had gone bad. So I removed them and reinstalled 2 of the original 4, all of which had tested OK after they were removed.

So I got there in the end, even if I did get a bit of a headache using a magnifying glass for so long!

I just hope it keeps working...

Thanks to all who helped.

[oddbodd]

Re: Fix for Benq FP737s 17" (Q7T3)

I'm in the middle of resoldering, and have just come across an unsoldered pin on T601. Is that right?

Edit: Answering my own question, I've see on post #244 there's a picture of the same board, with the same pin unsoldered.

[oddbodd]

Re: Fix for Benq FP737s 17" (Q7T3)

IC602 probably is - re solder it anyway wont do any harm 4 legs? cant see it on pic.
You should aso resolder those gray box caps with a k on between the 5707s and also the blue ceramic caps - and the inverter transformers and main transformer in fact if your good at soldering solder as much as you can be bothered with.

OK, thanks.

IC602 does have 4 legs.

Will resolder all, and report back...

[budm]

Re: Fix for Benq FP737s 17" (Q7T3)

Sch:
The inverter transformer driving circuits are setup as self Osc Royer OSC, if the MOSFET which is PWM driven at the Gate to provide variable DC (more dc more brightness) for the Royer Osc, if the MOSFET shorted out (jump Source and Drain), the inverter will be running at full mode disregarding the PWM IC is working or not.

[selldoor]

Re: Fix for Benq FP737s 17" (Q7T3)

IC602 probably is - re solder it anyway wont do any harm 4 legs? cant see it on pic.
You should aso resolder those gray box caps with a k on between the 5707s and also the blue ceramic caps - and the inverter transformers and main transformer in fact if your good at soldering solder as much as you can be bothered with.

[selldoor]

Re: Fix for Benq FP737s 17" (Q7T3)

Re touching may not be enough - You need to get some leaded solder to mix with the old solder then remove it -or most of it then resolder with new solder.

[oddbodd]

Re: Fix for Benq FP737s 17" (Q7T3)

Hi,
I just joined this forum, and have read through numerous posts to try and fix my Q7T3 Benq monitor.

I have been getting the "2 seconds to black" problem. Although, at first, after switching the monitor off and on a number of times, it would work OK.

There's nothing immediately apparent on the board itself. So, I tested the following, but replaced them anyway...

1) the 3A picofuse
2) the 4 2SC5707 transistors
3) the 2 FU9024N fets

... but no difference.

I have just retouched the solder on the inverters, and still no change... at first, anyway. After switching the monitor on and off a few times, I now get the Benq logo flashing every second or so.

So, any ideas where I go from here, please?

I also read that the octocoupler might need resoldering. Is this IC602 on my board? [48-L8302-A30].

I'm fairly new to a lot of this stuff, so thanks for any help.

[ronszon]

Re: Fix for Benq FP737s 17" (Q7T3)

Hi,

Thanks for the info in this thread, it saved me a screen! (Though I was thinking of buying a new HUGE one already... damn...)

I have two HP 1740, one of them first was not able to switch off the backlight (nice LCD-going-off effect, then white), then after a week it died completely.
It has inside a derivative of the Q7T3 board (48.l1g02.a01) for which I could not find an exact schematic... (annoying!) It is slightly different since it does not have the PF751 (Vinverter fuse). What happened is one of the MOS switches (FU9024) blew to short (that's probably the screen not going off anymore?) and one of the bipolar c5707 blew as well (that's the screen dying I guess).

I got a repair kit from ebay, replaced all transistors (4 c5707, 2 FU9024), replaced the (only) fuse PF701 (that's the fuse before the large diodes with heatsink) and it worked! Tadaaa!

Thanks again! I just wonder how much longer these old screens will live (so I can finally buy myself something bigger )

Kuba

BTW. I also resoldered the inverter's transformers. It indeed looked like there is some wear on the joints...

[pappa_smurf]

Re: Fix for Benq FP737s 17" (Q7T3)

Hi All
New guy from Mozambique,
MAN! I wish I had a Pinch of the Knowlwdge floating around this forum, Good going Guys.
I have a Benq Q7T3 which has been good for years, now it has died a quiet death.
No lights no nothing, have done a cursory test of trannies and such, resoldered all joints, did not remove solder just resoldered and nothing happens.
I am a hobbyest and don't know much, am also 1000Km from civilization and batle to get spares quickly, have to wait till I go go to South Africa from time to time to purchase.
Please tell me where to start to look for the problem, I do have the diagram and understand a bit about testing.
Any help will be much appreciated
Kind Regards

[bignick8t3]

Re: Fix for Benq FP737s 17" (Q7T3)

Hi all,

I have 2 Benq FP737s, 1 work's perfectly well the other well I'll elaborate...

When switched on the LED will light up green but the backlight will flick on and off randomly, the signal/picture is still there as when it's flickering on and off if you shine a light on it you can still see the image.

So it hasn't completely died yet. I have searched this thread and apologise in advance if these symptoms have been seen before.

Thanks in advance.

Nick

[soulraven]

Re: Fix for Benq FP737s 17" (Q7T3)

i have check the fuse and nothing, i also measured and is ok.
i am sure that a imperfect contact somewhere. any idea about that? or something to measure and determine if everything is ok?

[soulraven]

Re: Fix for Benq FP737s 17" (Q7T3)

i will check the fuse again tomorow
"the monitor enters in standby or exit from standby when i disconect the input cable."
i mean the d-sub cable between pc and monitor

[selldoor]

Re: Fix for Benq FP737s 17" (Q7T3)

Hi check the fuse again - if you can get to it, try very gently pressing on it ( With something insulated )while everything is switched on -may be bad contact?
If it is a flat cable connector did you clean it. If it is pins have you checked for bent or broken pins.
"the monitor enters in standby or exit from standby when i disconect the input cable."

Do you mean the input from the PC - you should not plug/unplug any internal cables when it is switched on.

[soulraven]

Re: Fix for Benq FP737s 17" (Q7T3)

thx,
i have check the fuse from the lcd panel and is ok,
but after that i have power again the monitor and is just work, no white screen, just work, but after a few hours or running ok, after i reconnect the monitor to power i get again the white screen. The last thing that i have work on it is the connector from the panel and the logical bord.
After that i have try again to check the connector, to check again the connection but nothing, still withe screen

any idea what about that? strange thing

[retiredcaps]

Re: Fix for Benq FP737s 17" (Q7T3)

the screen is white and nothing is displayed, only a few small lines colored.

1) You could have a blown SMD fuse on the panel card that runs the length of the monitor. The panel card is usually at the top of the monitor.

2) There could be a bad voltage regulator on the main board.

3) You could have bad, but not bloated, caps on the main board.

[soulraven]

Re: Fix for Benq FP737s 17" (Q7T3)

hi, please help me with a problem, i have a benq FP731 monitor with a strange problem,
the screen is white and nothing is displayed, only a few small lines colored.
i have try to press and the ribbon from the lcd panel to logical board, but nothing.
the monitor enters in standby or exit from standby when i disconect the input cable.

any ideea where is the problem?