Fix for Benq FP737s 17" (Q7T3)

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

Thanks for feedback. A bit strange one transistor is hotter. But all seems to be OK. The question that remainsis. What caused the original transistor/s to fail? In time this may be revealed.

[sirzur]

Re: Fix for Benq FP737s 17" (Q7T3)

In Australia, source for 2sc5707 is from WES Component
Source of IRFU9024N is from Radio Spares(out of stock) or Farnell Australia

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

Thanks the input. Useful to know. WES Components is a strange web site. If you search for 2SC5707 there is no indication that they have stock or the price. The search only indicates other suppliers in the US!!!!

Certainly Farnell have the IRFU9024N @ $3.60 plus heaps for delivery. RS Components actually do show stock @ $3.57 and can be bought over the counter locally. All prices +GST. Pity RS do not have 2SC5707.

[Krankshaft]

Re: Fix for Benq FP737s 17" (Q7T3)

I hate relying on E-bay for my parts.

I guess I could buy it from a parts distributor but they probably have like a 2,000 part minimum order and I'd have so many I'd be using them to level out the hill in my yard .

B&D has them but the price $4.00 each is insane.

http://www.bdent.com/search/search.j...FUV0OAodPy5t-g

Dalbani in the UK has them too but the price is about the same. If you're in the UK and want the parts faster then from the US this is for you.

http://www.dalbani.co.uk/catalogue/p...s.php?id=28283

Audio Lab also has them for a very reasonable price comparable to the E-bay sellers. The price is right if I need any in the future I will buy from them.

http://www.audiolabga.com/mal_cart/m...t_***on=Search

[sirzur]

Re: Fix for Benq FP737s 17" (Q7T3)

Yeah I knew about WES Component because I read about it on another site. I had to call them up to ask whether they carry the component and then ordered it.

You are right about Farnell - cost an arm and leg for delivery.

A question for everyone. I have just gone through the trouble of replacing all the 2SC5707 (not that any tested bad), recapped all bulging capacitors and replaced the IRFU9024. The monitor now works, but the soft start button on the front does not switch the CCF off. I know that the power to some of the circuit gets switched off because the LED on the power switch goes from blue to orange. The funny thing is that even though I turn the soft switch off (neither blue nor amber light), the CCF still stays on.

Also when I have no video signal connected to the monitor and switch the monitor on, there is a warning that there is no signal connected (against a black background). Then this gradually gets replaced by a progressively brighter screen (I suspect the LCD is turning off) and the soft switch LED light turns from blue to amber and the CCF stays on.

I have read earlier in the thread that this could be due to the BLT_ON line being constantly powered and I have checked the VGA board but have not noticed any obviously defective component. What steps should I take to troubleshoot. An alternative is for me to just switch off the monitor at the wall switch, but that is a pain

Thanks

[terry]

Re: Fix for Benq FP737s 17" (Q7T3)

I has the same problem (the CCF not going off) after lots of testing I found it was a faulty FU9024N.

[Krankshaft]

Re: Fix for Benq FP737s 17" (Q7T3)

Yeah I knew about WES Component because I read about it on another site. I had to call them up to ask whether they carry the component and then ordered it.

You are right about Farnell - cost an arm and leg for delivery.

A question for everyone. I have just gone through the trouble of replacing all the 2SC5707 (not that any tested bad), recapped all bulging capacitors and replaced the IRFU9024. The monitor now works, but the soft start button on the front does not switch the CCF off. I know that the power to some of the circuit gets switched off because the LED on the power switch goes from blue to orange. The funny thing is that even though I turn the soft switch off (neither blue nor amber light), the CCF still stays on.

Also when I have no video signal connected to the monitor and switch the monitor on, there is a warning that there is no signal connected (against a black background). Then this gradually gets replaced by a progressively brighter screen (I suspect the LCD is turning off) and the soft switch LED light turns from blue to amber and the CCF stays on.

I had the same problem with my HP (built by Benq Monitor) after replacing the shorted inverter switching transistors. It turned out one of the CCFL shutdown FETS was shorted.

These fets will either be SMT in a 4 pin package (as they were on my monitor) or they will be in a standard through hole package.

Based on the pics I've seen of the Benq FP737s power board its mostly through hole so most likely the FET in question will be easier to find and replace.

To test the faulty fet simply measure from source to drain with the diode function of your meter. The faulty one will measure 0.00 or short circuit in both directions.

To be safe just replace both so you won't have to do this again.

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

There are several possibilities. The most likely is the FU9024N or the drive transistor (Q752 or Q742) being a short, another is the transistor (Q761)that switches the power to the TL1451 chip. If the FU9024N or Q752 is a short the CCFL lamps will get excessive current (too bright) and there will be no brightness control. If the transistor to the TL1451 is permanently ON you should get brightness control and lamps continuously ON without the input BLT_ON.

Q752 & 742 can be replaced by a BC640.

Hope this helps.

[sirzur]

Re: Fix for Benq FP737s 17" (Q7T3)

Yes thanks. I have set this aside for the moment.

The original problem was that it urned on for a while and then turned off. I have replace all bulging and (other biggish) caps. Have replaced all the 5707's, 9024's, some of the A733 and H945s (by the way A733 and H945's can be bought from Rockby electronics. A733's are 2sa733 and H945 are 2sc945) and the problem still persist. When I replaced one of the 9024's I did not notice that the track was lifted off and even though soldered, the pin was not in contact with the track. That was the cause of the CCF not turning off. When I resoldered the pin correctly, the original problem manifested again but the CCF turned off properly (I would like to see someone explain this? - Oh the 9024 had to be replaced again as it appeared to be getting very hot and singeing the PCB). So my conclusions is that after replacing all the components, I have not really done any good. I am left with the option of replacing the transformers and/or the 1451 IC. I know the IC can be gotten from Radio spares. Unfortunately I have no way of testing the transformers and they will be expensive as well. So I am putting this aside for the moment until some other idea strikes me on how to repair.

Of course now another problem has manifested. In my last 2 dismantling and reassemble, there is now a 1" wide vertical blue/green stripe on the lcd, which I figure has to do with the VGA board....

Thanks for all the ideas so far

Cheers

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

Well you have had a lot of problems. It does seem that you are lacking the testing kit to take this project further. In hind sight it seems it may have been better to get a replacement PCB assembly. The vertical line may be due to a disturbed processing chip in the monitor or the ribbon connector may not be connected completely. I am sure you can work out the source of the problem.

[charlesrg]

Re: Fix for Benq FP737s 17" (Q7T3)

Dear All,

First thank you all for the posts, that helped me alot with the troubleshooting this monitor.


I've a question:

What would be a great spare for the 2C5707 since it's failing:
The MJE3055T (TRANSISTOR NPN 60V 10A TO-220 )
or
the MJE13007G (TRANS PWR NPN 8A 400V TO220AB)

Both available at digikey at 0.99 and 0.90 .


Also heard that the guy selling on e-bay also sends a solution for the caps to not burn again. Is that a true solution or is the guy telling to turn off the monitor on reboot ?

[charlesrg]

Re: Fix for Benq FP737s 17" (Q7T3)

Also some people had mentioned the 2N3055 anyone used that ?

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

There is nothing wrong with the 2SC5707. They fail due to weakness of the circuit design described earlier in this thread. the MJE3055 has been used. It is not up to the same performance but one user has made them last, for how long is not determined.

A simple way to protect the transistors is to switch off the monitor during the first computer post following a bios change.

[agentsmithitaly]

Re: Fix for Benq FP737s 17" (Q7T3)

Hi everybody!

I have a faulty Q7T3 too and found this very interesting topic. Unfortunately I have little or no knowledge in electronic repair

I checked the board and found the small 3A fuse open (didn't desoldered it). Then I desoldered all the four 2SC5707 in order to test them with a digital multimeter, as suggested here http://www.kpsec.freeuk.com/components/tran.htm
It appears they perform correctly (base-emitter and base-collector like diodes, collector-emitter no conduction), though I have read this is only a basic test.

What do you suggest me to do? Anything else to test? I have also brand new 945 and 733 transistor to replace.
Is it correct to desolder transistors before testing?
I haven't found the Bel Fuse MS 3A fuse, an electronic repair shop gave me for free a 3.15A 250V fuse, could be ok or over-spec? I found also a 2.5A 125V.

I ordered eight 5707 transistors, but they shipped one in a normal style, and the other seven in SMD style (the three pins are much shorter).
If you suggest me to replace all the trannies, can I solder them on the other side of the PCB or could be a problem?

Thank you for your help, and sorry for all these questions, I have read the entire topic but can't decide by myself, I'm a n00b

Agent Smith

[dany boy]

Re: Fix for Benq FP737s 17" (Q7T3)

hello,
i have a faulty benq q7t3.
i bought 4 replacement 2sc5707's and soldered them in but the screen still does not light up.
when i turn the monitor on i can see a very very faint benq logo for a couple of seconds and thats it.

any help would be much appreciated, does anyone know what i could try next?


Thanks,
Dan.

[Krankshaft]

Re: Fix for Benq FP737s 17" (Q7T3)

Hi everybody!

What do you suggest me to do? Anything else to test? I have also brand new 945 and 733 transistor to replace.
Is it correct to desolder transistors before testing?
I haven't found the Bel Fuse MS 3A fuse, an electronic repair shop gave me for free a 3.15A 250V fuse, could be ok or over-spec? I found also a 2.5A 125V.

Agent Smith

If the 3 amp fuse is blown it blew for a reason if the trannies are ok check the capacitors for bulging this is a common problem. As for the pico fuse you will need a 3 amp replacement you can order them from Digikey.

Check for cracked solder joints around the power board especially around the inverter transformers.

If the trannies measure a voltage drop one way from base to collector and base to emitter they are probably fine although I find them being ok to be odd.

Be sure to check the inverter ON / OFF FETs measure from source to drain they have the designation IRU something or other I believe. This thread has their part number posted somewhere.

Also check the switching supply FET (on the small heatsink) and the secondary rectifiers for shorts as well. If all of the above check out replace the fuse and try powering up the montior.

As for the 2707s these are the type that you are looking for the ones in the through hole package not the SMT package:

http://search.ebay.com/search/search...fsop=32&fsoo=2

[Krankshaft]

Re: Fix for Benq FP737s 17" (Q7T3)

hello,
i have a faulty benq q7t3.
i bought 4 replacement 2sc5707's and soldered them in but the screen still does not light up.
when i turn the monitor on i can see a very very faint benq logo for a couple of seconds and thats it.

any help would be much appreciated, does anyone know what i could try next?

Thanks,
Dan.

Check for bulging capacitors they can cause this.

Also check for a blown pico fuse it will be around 3 amps these tend to go south when the inverter transistors go.

[Newbie2]

Re: Fix for Benq FP737s 17" (Q7T3)

I have a BenQ FP731 monitor that recently stopped working. Along with an experienced electrical enginner I found that the four 2SC5707 transistors (on Q739, Q740, Q759, and Q760 I think) and the 3A fuse (on PF751 I think) on the inverter area of the board failed, and Digikey doesn't have the 2SC5707 transistors. After looking at a whole bunch of bipolar transistors on Digikey, my buddy said that the D44H11 transistor was the best alternative.

I mentioned that people have had success using the MJE3055 transistor, and then I pulled out its spec sheet and my buddy said they may work but they'll run very hot and only good as a temporary solution.

Are the D44H11 transistors good as replacements for the original 2SC5707 transistors inside these BenQ Q7T3-based (FP731, FP737s, etc.) monitors?

[waterppk]

Re: Fix for Benq FP737s 17" (Q7T3)

Hello,

First off, awesome thread!

Quick question, through the picofuse, PF751, what are you guys seeing as a typical current draw? I was running at about 1.5A on start up and inching towards 2.2A, is this inline what the you've seen or?

On another board, someone suggested replacing the C5707's with MJE3055T's (USA Radioshack part, ~$1/each with no shipping), do you see any sustainability problems with this or?

Thanks!

[starfury1]

Re: Fix for Benq FP737s 17" (Q7T3)

On another board, someone suggested replacing the C5707's with MJE3055T's (USA Radioshack part, ~$1/each with no shipping), do you see any sustainability problems with this or?

Replacement with these if I remember correctly is "Not" advised.

EDIT see post above

https://www.badcaps.net/forum/showpo...5&postcount=93

there is a web page that suggests this and I think the creator as even posted in this thread.
(think it was cause he couldn't get suitable replacements so used what he could get from local hobby store, he was from NZ I think too)

If you got through this thread or (there is another similar) look at Davmax's replys

Davmax did spent a lot of time analyzing this problem and posted possible reasons to why this happens and what you should do

Also (from memory) you should "Replace ALL 4 Transistors"
(and possibly check or mod a few things)
I think he also suggests "suitable alternatives" for transistors


HTH

Welcome

Cheers