Fix for Benq FP737s 17" (Q7T3)

[enterthehatrix]

Re: Fix for Benq FP737s 17" (Q7T3)

Greetings from the UK.

Our work office is loaded full of these benq monitors (all Q7T3). Needless to say they'll all eventually fall to this problem as we've had 2 die already out of 14 identical models.

Anywho, I was wondering if anyone could clarify exactly what I should replace in order to get it working (identifier code on board, and part name / code) and any basic and simple preventative measures I could take to stop it happening in the future, if not stop it happening quickly again in the future.

The reason I ask is that the information I've read here conflicts with some information on another site. However, I trust the judgement from this forum more since there are several of you vs the writer of the article I read.

[msubzwari]

Re: Fix for Benq FP737s 17" (Q7T3)

Greetings from Karachi, Pakistan. This thread is a treasure trove for Benq affectees.

I have a 5 years old Benq 17 incher. Model is FP767-12. It gave up on me couple of days ago. While searching on the net for repair/service centre, I stumbled into these forums & boy am I glad that I did. The board/circuit is the same as being discussed/shown in photographs posted in this thread.

To cut the long story short, the 3A fuse & one of the 2SC5707 were busted in my board. I could not find 2SC5707 in the market but one shop had 2SC5706. It has slightly lower Collector & Base Current max ratings compared to 2SC5707 but rest of the specs were a close match. So decided to go for it instead of going the TIP3055 way.

I replaced one pair but the lamps did not work. Thinking the C5706 are busted, I took them out & tested. They were Ok.

Checked Hfe value of 5706 and it was around 320. Checked the working 5707 and it has Hfe of 380. I bought some extra C5706 and two of those gave me Hfe reading of 400 & 395. So removed the ones I soldered earlier and installed the higher Hfe rating C5706 pair. That brought the life back to the display.

Packed it up, connected to PC, turned it on.....nothing. Opened it up again, checked all of my soldered components which seemed fine. Double checked any problems in the caps, nothing obvious observed.

Decided to resolder anyway & while I was at it, resolderd all transformer legs. Powered it up and it was alive again. Packed it up again & it has been working well since then.

I just turned it off after being used for about an hour..so far its holding.

My sincere thanks to all the contributors to this thread for sharing their valuable insight into this very interesting problem.

[ozcar]

Re: Fix for Benq FP737s 17" (Q7T3)

I would just like to thank all of you who contributed to this thread. When my FP737s died last week ago I was about ready to give up on it and get a new monitor. Then I found this thread, and one 2SC5707 and one fuse later I am back in business. I resoldered the transformers too - not that I could see any problem there.

With a bit of luck maybe it will keep going for another few years. If it dies again I might consider the suggested circuit changes.

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

Did you resolder all the inverter transformer connections? It sounds as thoughthe 5707s are gone again. There are claims that the resoldering will enable a permanent fix. However as you have seen I have implemented the current limit system on three monitors with no further failures. This method catches all heavy overcurrents FAST (10usec).

[epiman46]

Re: Fix for Benq FP737s 17" (Q7T3)

First, a big thankyou to all on this thread. I had two BENQ 737s that died, more or less simultaneously. I replaced the SC5707s, and the 3A fuse, and they both worked. Yay! For not quite a week. Then they both died.

One will run for about 5 minutes, fade (get dim) and then croak. The image is visible under inspection with a strong light. Giving it a 10-minute rest will give me about 5 minutes of usable function. The other, just flashed, then died. Again, the image is visible on strong illumination.

So replacing a few transistors has not solved the problem. I am not interested in going that route again, unless I have a solution that addresses the problem of why they failed in the first place. I have a few questions:
- Which is the better candidate for repair?
- has anyone else had any success with Davmax's current-limiting protection circuit?
- should I be recapping, on general principles? I don't see any bulges, or discharge. All the solder joints looked good.

[bizu]

Re: Fix for Benq FP737s 17" (Q7T3)

Thanks to Davmax for initiating this thread.
I have a Benq FP731 and the problem was just the same as most others have found.
After replacement 4x2SC5707 2xFU9024 and the fuse 3A all was well again. I resolder joints on the inverter transformers.

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

I forgot to advise that if the FU9024N (Q805) is burned up this is unusual and will most likely mean other components have failed. Normally the correct micro fuse would prevent this problem. I wonder if someone used an incorrect replacement fuse!!!

I want to ask you same question.I have LCD Monitor Benq , But in the electric bus the element Q 805 is burned and I can't to read what is the element and change it. If you cant saw me this information I will be very happy.

[pecolt]

Re: Fix for Benq FP737s 17" (Q7T3)

[pecolt]

Re: Fix for Benq FP737s 17" (Q7T3)

Thank for that information. I'm so glad.
I have some question. I have one LCD TV monitor "REFLEXTION" 22inch model TDD2200 with DVD player integrate. Can send me some all electric bus because there have many burned elements who I can't read.

[pecolt]

Re: Fix for Benq FP737s 17" (Q7T3)

Thank for that information. I'm so glad.
I have some question. I have one TV monitor "REFLEXTION" 22inc. model TDD2200 with DVD player integrate. Can send me some all electric bus because there have many burned elements who I cant"t read.

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

So Q805 is FU9024N in Q7T4. Thanks Freegeekvan

[FreeGeekVan]

Re: Fix for Benq FP737s 17" (Q7T3)

I want to ask you same question.I have LCD Monitor Benq , But in the electric bus the element Q 805 is burned and I can't to read what is the element and change it. If you cant saw me this information I will be very happy.

I believe you are working on a Q7T4. I put up a different thread here:

https://www.badcaps.net/forum/showth...6397#post56397

It contains a picture of the part placed at Q805, plus some other information.

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

I want to ask you same question.I have LCD Monitor Benq , But in the electric bus the element Q 805 is burned and I can't to read what is the element and change it. If you cant saw me this information I will be very happy.

I have searched the circuits of the FP737s and there is no Q805. This is a problem. Please check again.

davmax

[pecolt]

Re: Fix for Benq FP737s 17" (Q7T3)

I want to ask you same question.I have LCD Monitor Benq , But in the electric bus the element Q 805 is burned and I can't to read what is the element and change it. If you cant saw me this information I will be very happy.

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

Jim,

If you following the latest small change to the mod you should have great success. Just a matter of connecting it all correctly and cutting the right tracks.

I found it more convenient to use one 0.082 resistor for the current sensing than the two in parrallel (0.1 and 0.56).

The original circuit with a 2.7K resistor in parallel with the 1uF cap (now 270) tended to trip easily making it appear that there is a monitor problem.

Yes make sure of those soldered joints.

[arneson]

Re: Fix for Benq FP737s 17" (Q7T3)

I've got all the components to try this except the FU 9024n,
which is only a couple bucks.
When I get time I'll pull this board again to give it a try.
I had already tried your first idea adding limitting resistors with success until I reasembled the monitor and it was dead again.
That leads me back to the possability of the transformer solder joint leg issue.
Thanks for putting a lot of work on that.
If I have your mod working cool and bright I'll certainly post back again.

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

The new layout detail is attached. Note the original value for R767 of 2.2k need not be changed to 680. See circuit diagram.


To Freegeekvan

If you do the current limit mod you will not blow the transistors again. If for some reason the current limit is exceeded the controller chip will lock out drive to the MOSFET transistors suppling each inverter. It can be reset by power removal or loss of video signal.

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

I have recently discovered that a slight change in my current limit modification is required to better cover variations in the BC640 transistor.

The latest mod diagram is attached together with the parts list.
Note the current sense resistor can be one 0.082 1% resistor or the first two resistors in the parts in the parts list.



I will post the new component layout tomorrow.

[arneson]

Re: Fix for Benq FP737s 17" (Q7T3)

I wear my red green 3D goggles.
The board looks all purple.

[kc8adu]

Re: Fix for Benq FP737s 17" (Q7T3)

these units have lots of solder joint issues.
mostly at the transformers but can be anywhere on the psu/inverter.
look closely for ringcracks and pads showing bare copper where the solder did not flow out properly.
these are a job for your geeks with good vision and a good magnifier lamp.