Fix for Benq FP737s 17" (Q7T3)

[electron]

Originally Posted by davmax

Some have asked for PCB photos. Well I have just fixed and modified another monitor and taken photos.

This monitor was received with a damaged ribbon connector. This is usually because the release mechanism is not understood. To release the ribbon cable lift /rotate the black locking bar outward from the centre of the top edge. Do not force.

Update: My PCB board matches this one exactly. So I have the same model as the one here. Whats the full model number of this screen?

[LETSOC]

hy i have the same problem ..... with the Benq FP737s 17" i dont have any lights but if you look closer at the monitor you can see the desktop


sorry for the post, please help me what i have to do ... ?
(sory for my english im romanian)\



Thx,

[Newbie2]

Originally Posted by LETSOC

hy i have the same problem ..... with the Benq FP737s 17" i dont have any lights but if you look closer at the monitor you can see the desktop


sorry for the post, please help me what i have to do ... ?
(sory for my english im romanian)\



Thx,

Either you have a transistor problem or the backlights have burnt out.

If your backlights are burnt out, consider buying a new monitor if the 2SC5707 transistors are still good.

[mattmozz]

thank for the info my monitor is now back up and running

[mattmozz]

i had a similar problem i just re-soldered all of the joints near all of the transistors and near where all of the connections are to the screen (back light) and followed them back and just removed all the old solider and added fresh.

[FreeGeekVan]

Originally Posted by davmax

It is not a good idea to have a 3A slow blow fuse "not recommended if it is to protect the transistors". A fast fuse may save the transistors.

agentsmithitaly

I suspect blown transistors again.
1. Make sure that all the inverter transformer connections are resoldered
2. Use a fast 3A fuse
3. Check the MOSFET in each circuit Q751 & Q743 (FU9024N) they should not read a short circuit.

http://www.lcdrepair.us/fu9024n.html

See my experiences earlier in the thread. These transistors are not well protected by the circuit design. I modified the circuit and the monitor is very well protected.

Hello,

I help coordinate Free Geek, which is a non-profit computer recycler and education centre. We see tonnes of equipment come through our doors monthly. Lately we have seen an increase in LCD's.

Many of these LCD's for recycling we can bring back to life. We have seen our fair share of the Benq/Dell nasties. Our past repairs have worked well(replacing C5707 and fuse), however lately we have been having a lot of come backs.

Presently we sit on 15-20 Dell/Benq type LCDs with the Q7T3. I wouldnt mind folks opinions on the best way to move forward. I would especially like to hear from Davmax, after reading all the effort you have put into this. Should we do the mod job you worked out, or stick to replacing C5707 and fuses with a re-soldered inverter transformer connections(which we have done in the past but only on one or two of the repairs.)

The last 10 repairs we have done came back. We had just replaced the two C5707 and the fuse, there was no re-soldering of the inverter transformer. Was this the cause of the blown C5707 again?

We have a big job ahead of us, and don't want anymore come backs. Suggestions or comments welcome!

--
David

http://freegeekvancouver.org

[kc8adu]

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.

[arneson]

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

[davmax]

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.

[davmax]

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.

[arneson]

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]

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.

[pecolt]

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]

Originally Posted by pecolt

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

[FreeGeekVan]

Originally Posted by pecolt

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:

http://www.badcaps.net/forum/showthr...6397#post56397

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

[davmax]

So Q805 is FU9024N in Q7T4. Thanks Freegeekvan

[pecolt]

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.

[pecolt]

Originally Posted by pecolt

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]

[davmax]

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!!!

Originally Posted by pecolt

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.