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Old 10-16-2008, 03:25 PM   #1
FreeGeekVan
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Default Benq Q7T4 FP71G

Working on a Benq FP71G model Q7T4. So far have found blown fuse, bad solder job on cap at C826, 2 blown transistors (those infamous C5707). Also included in attached photos is the MOSFET part number I think user "pecolt" was looking for in the Q7T3 thread.
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File Type: jpg q7t4-PCB.jpg (269.0 KB, 516 views)
File Type: jpg q812-q805.jpg (118.1 KB, 404 views)
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Old 10-27-2008, 08:53 AM   #2
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Default Re: Benq Q7T4 FP71G

interesting so far i had the same bad soldure at the same part and the 2 blown transitor. C826 broke but no broken fuse, still looking to find what else may have broken ive tested the 4 transformators :t804 to t801 and they are all fine. got any leads to what it could be?
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Old 10-27-2008, 09:09 AM   #3
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Default Re: Benq Q7T4 FP71G

"Replace Q808,Q809 --> type 2sc5707
C826 0.22uF 160v
C712 1000uF 10v
PF801 3A wicked Fuse"
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Old 10-27-2008, 12:32 PM   #4
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Default Re: Benq Q7T4 FP71G

Also check the FU MOSFETs one of them usually likes to open.

If one is open both of the monitor blacklights won't turn off when you hit the power button.

Oh yes and were not talking a standard 3 amp glass fuse it's a pico fuse it's a through hole component.

It is black and almost the same size as an IN400X diode but it will say Buss (a fuse company) in green with the voltage and amperage on it.
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Last edited by Krankshaft; 10-27-2008 at 12:38 PM..
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Old 12-24-2008, 09:03 PM   #5
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Talking Re: Benq Q7T4 FP71G

Wow! Just fixed a friend's benQ, and the culprit was also a bad solder joint on C826. Those transistors must pump out a lot of heat, and melt the solder next to them.
Thanks to all.
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Old 03-22-2009, 08:50 AM   #6
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Default Re: Benq Q7T4 FP71G

i am having the same problem with mine, if anyone is still willing to help, solder on C826 looks fine and broken on mine, will re solder that, also, there is solder missing on one little spoke on the big yellow thing, will re solder them both tomorrow will start with C826, and leave other off and than try it, dosent appear to have had solder there b4 hand

screen turns on for 1 sec, and flash's off
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Old 03-22-2009, 09:19 AM   #7
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Default Re: Benq Q7T4 FP71G

Probably C5707 ics. I had 2 of those last week, both the AC and DC versions. You're going to have to buy the parts. Just fixing solder joints isn't going to do it.
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Old 03-22-2009, 10:29 AM   #8
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Default Re: Benq Q7T4 FP71G

how much do you think it would cost to fix all up, not really worth throwing screen away i couldent find C5707 some solder is broken on mine but dose not look to bad, ill just solder it all up, and see how it goes, if it dosent work, will have to take it to the next step and get some parts for it. and see how it goes, how much would it cost for all most common parts which go???
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Old 03-22-2009, 02:03 PM   #9
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Default Re: Benq Q7T4 FP71G

Quote:
Originally Posted by zerophotos
how much do you think it would cost to fix all up, not really worth throwing screen away i couldent find C5707 some solder is broken on mine but dose not look to bad, ill just solder it all up, and see how it goes, if it dosent work, will have to take it to the next step and get some parts for it. and see how it goes, how much would it cost for all most common parts which go???
FIXITNOW gave a list of parts above. Google lists a number of sources for the 2sc5707, several have it for under $2.00 each with no minimum order. The two caps should cost under $1.00 each. The picofuse might be the expensive part - you'll probably have to buy a 5-pack for $5.00. Add in shipping and it should still cost less than $20, delivered for everything on his list. Of course, this is for the USA.

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Old 03-28-2009, 03:04 PM   #10
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Default Re: Benq Q7T4 FP71G

Hi,

I have the same Problem as FreeGeekVan. So far I replaced the (obviously blown) c712 as well as the c707, c708 and c709 (just in case). I furthermore put in an new Q805 (shortcircuited with IRFU 9024N and replaced al sc5707 with sc5707. I tested the fuse PF 801 and a current can run through. The symptom of a white screen with running backlight has not changed. Does anybody have an idea how to fix my Q7T4? I can not test capacitators so I do not know which other ons to replace. Furthermore my standart electronics dealer (in Germany) does not have any replacement for the c826 which was also one of the most common flaws. I will see if I can get that one elsewhere...

Cheers,

Canadan

Last edited by canadan; 03-28-2009 at 03:09 PM..
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Old 03-28-2009, 08:49 PM   #11
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Default Re: Benq Q7T4 FP71G

Quote:
Originally Posted by canadan
Hi,

I have the same Problem as FreeGeekVan. So far I replaced the (obviously blown) c712 as well as the c707, c708 and c709 (just in case). I furthermore put in an new Q805 (shortcircuited with IRFU 9024N and replaced al sc5707 with sc5707. I tested the fuse PF 801 and a current can run through. The symptom of a white screen with running backlight has not changed. Does anybody have an idea how to fix my Q7T4? I can not test capacitators so I do not know which other ons to replace. Furthermore my standart electronics dealer (in Germany) does not have any replacement for the c826 which was also one of the most common flaws. I will see if I can get that one elsewhere...

Cheers,

Canadan
I've seen several references indicating a white screen is often caused by a blown smd fuse on the LCD panel itself.

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Old 03-28-2009, 08:59 PM   #12
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Default Re: Benq Q7T4 FP71G

Quote:
Originally Posted by PlainBill
I've seen several references indicating a white screen is often caused by a blown smd fuse on the LCD panel itself.

PlainBill
Yep, I second that. The 5v rail is not reaching the panel logic board. Look for a fuse near the input connector and see if it is blown.
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Old 04-01-2009, 02:53 AM   #13
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Default Re: Benq Q7T4 FP71G

Hi,
I read that reference, to. But I thought that the respective fuse is pf 801 which I have tested and found to be OK. There is however a glass fuse near the power input. I'll check that one.
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Old 04-01-2009, 08:26 AM   #14
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Default Re: Benq Q7T4 FP71G

the fuse you are looking for is not on the 2 boards that are pictured earlier in thread, they are on the screen panel,usualy under a metal cover that usualy has 3 tiny screws to remove to get at it, its very small not much bigger than pinhead,
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Old 04-01-2009, 12:42 PM   #15
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Default Re: Benq Q7T4 FP71G

Ok, I found the culprit and the fuse you mentioned seems to be blown. I am now thinking of hotrwiring it due to the fact that I don#t have the tools to put in a new fuse that small.
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Old 04-01-2009, 01:02 PM   #16
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Default Re: Benq Q7T4 FP71G

Quote:
Originally Posted by canadan
Ok, I found the culprit and the fuse you mentioned seems to be blown. I am now thinking of hotrwiring it due to the fact that I don#t have the tools to put in a new fuse that small.
You don't have a soldering iron?

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Old 04-01-2009, 11:15 PM   #17
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Default Re: Benq Q7T4 FP71G

Quote:
Originally Posted by PlainBill
You don't have a soldering iron?

PlainBill

And Toasty criticized my 99c soldering iron.. at least I had one
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Old 04-03-2009, 11:54 AM   #18
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Default Re: Benq Q7T4 FP71G

I do have a soldering Iron, but it is let's say quite one the brink of destruction... It was a fairly cheap one and I can't get replacement tips. To replace the transistors I had to use up quite an exxesive amount of sandpaper on it. But I will probably try to replace the fuse anyway.

Last edited by canadan; 04-03-2009 at 11:56 AM..
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Old 04-03-2009, 01:15 PM   #19
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Default Re: Benq Q7T4 FP71G

Quote:
Originally Posted by canadan
I do have a soldering Iron, but it is let's say quite one the brink of destruction... It was a fairly cheap one and I can't get replacement tips. To replace the transistors I had to use up quite an exxesive amount of sandpaper on it. But I will probably try to replace the fuse anyway.
First of all, get a decent soldering iron. You don't need a $200 (US, about $75 Canadian ) soldering station with digital temperature control, but you deserve one where you can at least replace the tips.

If there is sufficient clearance you don't even have to remove the old fuse, just solder the new on on top of it.

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Old 04-04-2009, 05:09 PM   #20
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Default Re: Benq Q7T4 FP71G

Quote:
Originally Posted by PlainBill
First of all, get a decent soldering iron. You don't need a $200 (US, about $75 Canadian ) soldering station with digital temperature control, but you deserve one where you can at least replace the tips.

If there is sufficient clearance you don't even have to remove the old fuse, just solder the new on on top of it.

PlainBill
I started like him, but as things started to roll well, Toasty suggested something that's obvious but I needed that someone (him, in this case) told it to me to do it : get a decent Soldering Iron. As this was/is my main activity, I started with a cheap one because I didn't want to invest in something that maybe would not be uses so much. But now I changed the equipment because it is used and I will probably upgrade again soon. I understand his situation, and advice that he does the same as I : upgrade.
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