LCD 19" BENQ T905 problems

[budm]

Re: LCD 19" BENQ T905 problems

Check the black fuse PF801 which supplied the B+ to the backlights inverter circuit, it should be <1 Ohm.
This board is also know for bad solder joints, especially around the Inverter transformers, C5707 transistors and MOSFET q805/812, etc. Those transistors should also be checked for shorts or low resistance leakage.

[selldoor]

Re: LCD 19" BENQ T905 problems

First test the fuse PF801

[manthi]

Re: LCD 19" BENQ T905 problems

here they are

[manthi]

Re: LCD 19" BENQ T905 problems

1st step is open it and take photos of the boards.

ok lets go then

[Rtech]

Re: LCD 19" BENQ T905 problems

1st step is open it and take photos of the boards.

[manthi]

Re: LCD 19" BENQ T905 problems

hi guys
i have a benq t905, it has been sitting in my basement for several years now, it display the very common problem many benq monitor have, which is when you turn pc on the light on monitor goes from orange to green, but it doesn't display anything (black screen).
i have never tried soldering, but i think it could be a good opportunity, trying to resuscitate that monitor.

[selldoor]

Re: LCD 19" BENQ T905 problems

Well done ! - I was working towards a power switch problem.
These boards do however have a repeated problem with bad joints
so you should still resolder as suggested.

[hua3]

Re: LCD 19" BENQ T905 problems

I have resolved the power led off problem with very simple way. Considering that no any caps blown and all fuses are ok, moreover the output of 5V and 3,3 V from the main board to the AD board are correct, so I think no any problem from the main board. Checked the switch resistance, I found it is variable by itself in the order of hundred ohms. It is clear an electric leaks problem. So I just clean the switch by using WD-40 in a few minutes, the resistance goes to normal. Then plug the electric power cable and turn on the switch. The power led is ON and the monitor works perfectly as before!!! Hope it is helpful to others with same problem.

[selldoor]

Re: LCD 19" BENQ T905 problems

In all this thread I cant actually see a decent picture of the main board.
Can you post one - both sides of the board. Is the power switch cable connected to the main board?

You should also do this - if you have not already
https://www.badcaps.net/forum/showpo...2&postcount=21

[hua3]

Re: LCD 19" BENQ T905 problems

The voltage looks ok.On the right side of the board is the connector to the logic board,which is normally fed with 5V.The Board is usually marked as to what is on each pin on that connector,so see if you have 5v between the 5v pin and ground,which will also be on that connector.measure this with the logic Board not connected,and then try with it connected,and advise.

Thanks very much for your king advise. I checked the pin connector voltage: before connecting to the logic board, pin 1 to 6 is 0V to ground, and pin 7,8 is 5V, and pin9,11 is 3.3V, . After connecting to the logic board, only pin 1 changed to 1.3V, others remain unchanged. In this case, can we say that the power board is OK? And then what causes the power off (no orange led light, no green light)? Or the power switch no function?
I remember one month ago the orange led cannot change to green light. After unplug and plug the power cable and press the power switch many times, it finally recovered. I tried the same this time, but no way. So should I check the power switch, and how to do?

[Rtech]

Re: LCD 19" BENQ T905 problems

Hello there,

Here are my symptoms and then the question

After some 7 or 8 years of faithful service and it failed to come on one morning.
I power off every night.

The green light flashed as already spoken about and sometimes the benq logo flashed.
I unplugged the VGA cable and the logo would hang on for 2 or 3 secs. With constant trying I could get it going and so I left my pc and monitor running. After power off, nothing , morte !!

Question --- How do you get inside.??? I have taken off every screw but the back will not come off.

The surround and case are also held together by plastic connectors.Try putting your fingers under the top of the surround and try and gently pull up from the screen,that should then let you work all the way around the monitor.If the top does not give way,then one of the sides or bottom will.

[Rtech]

Re: LCD 19" BENQ T905 problems

Dear Selldoor,

Thanks for your quick reply. The voltage on the 400v cap c605 = 316V.
the 2 fuses measured on board are 0 ohm for f 601, and 0 ohm for the picofuse fp 801 respectively. I attached here the pictures of board both sides. Please help me to find the problem and give me instruction for resolving it.

The voltage looks ok.On the right side of the board is the connector to the logic board,which is normally fed with 5V.The Board is usually marked as to what is on each pin on that connector,so see if you have 5v between the 5v pin and ground,which will also be on that connector.measure this with the logic Board not connected,and then try with it connected,and advise.

[David59400]

Re: LCD 19" BENQ T905 problems

Hello there,

Here are my symptoms and then the question

After some 7 or 8 years of faithful service and it failed to come on one morning.
I power off every night.

The green light flashed as already spoken about and sometimes the benq logo flashed.
I unplugged the VGA cable and the logo would hang on for 2 or 3 secs. With constant trying I could get it going and so I left my pc and monitor running. After power off, nothing , morte !!

Question --- How do you get inside.??? I have taken off every screw but the back will not come off.

[hua3]

Re: LCD 19" BENQ T905 problems

Dear Selldoor,

Thanks for your quick reply. The voltage on the 400v cap c605 = 316V.
the 2 fuses measured on board are 0 ohm for f 601, and 0 ohm for the picofuse fp 801 respectively. I attached here the pictures of board both sides. Please help me to find the problem and give me instruction for resolving it.

[hua3]

Re: LCD 19" BENQ T905 problems

Dear Selldoor,

Thanks for your quick reply. The voltage on the 400v cap c605 = 316V.
the 2 fuses measured on board are 0 ohm for f 601, and 0 ohm for the picofuse fp 601 respectively. I attached here the pictures of board both sides. Please help me to find the problem and give me instruction for resolving it.

[selldoor]

Re: LCD 19" BENQ T905 problems

What voltage on the 400v cap?
Which fuse?
We need pictures
Welcome to the forum-
We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246

It will be useful if you can say what the supposed fault was and a bit about yourself - skills tools etc.

[hua3]

Re: LCD 19" BENQ T905 problems

Hi 2 All,

I got the new parts (IRFU9024Ns) recently. So I mannaged to change one 9024N and pico fuse 3.A. Guess what! Monitor is up and running. I'll let it run for a while to see if the fix is permanent. So far it seems that IC 52 CJ5YK TL1451A is good. And I think it will be for some time

Thanks for reading and replying. I hope this thread will help to someone.

See ya

Hi all,

My LCD 19" BENQ T905 has the same problem: no power and no light of the power led. I checked that all the caps are ok (not blown), fuse is not broken, all the IRFU9024 have no any fried evidence. There is voltage on the 400 V cap when connect the power plug. Any one can help me to restart the monitor?

[jet]

Re: LCD 19" BENQ T905 problems

Hi All,

My first post here. Has anyone sourced an equivalent part to the FU9024N. I am in Canada and would like to find some local. Seems to me that part is week anyway. I read in another thread of someone modifying the circuit around the FU9012N but the link was dead. Any help appreciated.

Joe

[jetadm123]

Re: LCD 19" BENQ T905 problems

I have already done all these sorry forgot to mention it and i have read the forum also . Could it be the 1200ap40 that is causing the problem?

Good focused photos of the top and bottom of YOUR power board will help members point things out for you to check. There were different variations of your power supply used in the T905 and without photos, it's difficult to provide help. Use the "manage attachments" option to attach your photos.

[^Active^]

Re: LCD 19" BENQ T905 problems

I have already done all these sorry forgot to mention it and i have read the forum also . Could it be the 1200ap40 that is causing the problem?