Benq T701 and unknown fet's smd code

[Davi.p]

Hi, i have taken this monitor to repair, :L unfortunately it doesn't have the common inverter problem, it has a visually blown smd FET on the videoboard with code A1VB-1H .. 1H doesn't matter i think but i'm unable to find the mean of marking code to get datasheet or specs to exchange it , can anyone help me? The package is the very small 3 pin very common one. Big bye from Italy..

[aliasdck]

Re: Benq T701 and unknown fet's smd code

I haven't been able to find anything based on what you've provided.

Is it possible it is the reset controller for the microprocessor? How is it labelled on the video board (for example D13 or U10. A picture may help us identify it).

What symptoms does the monitor exhibit?

[Davi.p]

Re: Benq T701 and unknown fet's smd code

OK, i don't know how can i search, i've read another post here about the
same problem, the symptom is total white, so no video, i'm able to switch on/off normally. I try to search now.. the fet is very close to the lvds output cable and the drain is connected to the bigger el.lithic cap. of 100/25v.. if i can i post a picture link,
bye and thanks much!

[PlainBill]

Re: Benq T701 and unknown fet's smd code

OK, i don't know how can i search, i've read another post here about the
same problem, the symptom is total white, so no video, i'm able to switch on/off normally. I try to search now.. the fet is very close to the lvds output cable and the drain is connected to the bigger el.lithic cap. of 100/25v.. if i can i post a picture link,
bye and thanks much!

It's likely the blown transistor switched power to the panel. It should be a fairly easy job to identify a suitable replacement. The questions are 'Why did it blow?', and 'What other components were damaged?'

PlainBill

[Davi.p]

Re: Benq T701 and unknown fet's smd code

This is the picture, my phone isn't able to shoot at close dist. so ..
http://web.tiscali.it/bps_impianti/VCard-BenqT701.jpg
click with shift pressed so open in new window..

to Pl.Bill: ah yes was the switch to power panel, the reason it blown i don't know
but i'm searching the forum to see if that person had fixed by only replace the only
transistor, i hope, but why you say it's easy to replace? thanks for now..

[PlainBill]

Re: Benq T701 and unknown fet's smd code

This is the picture, my phone isn't able to shoot at close dist. so ..
http://web.tiscali.it/bps_impianti/VCard-BenqT701.jpg
click with shift pressed so open in new window..

to Pl.Bill: ah yes was the switch to power panel, the reason it blown i don't know
but i'm searching the forum to see if that person had fixed by only replace the only
transistor, i hope, but why you say it's easy to replace? thanks for now..

I'm going to use an analogy here, so bear with me. That FET acts as a relay - it switches power to the display - it is either on or off. To find a suitable replacement you have to find a FET that is available in the same package, will handle the same (or greater) current, can withstand the same voltage, and turns 'On' with the same level signal.

From the remains you can identify the package type.

The panel PROBABLY uses 5 volts, but I believe some use 15 volts. The FET has (had) three terminals. One should be connected to power traces to the panel connector. One is connected to the power bus on the logic card. The third is the gate. Measure the voltage on the power bus.

Measure the voltage on the gate terminal when the power LED on the monitor is on, and again when it off (turned off, not unplugged). Now you know if you need an enhancement or depletion mode FET.

Last, measure the current the panel takes. It's probably less than 2 amps.

Any of the selection engines at places like Mouser and Digikey will allow you to select parts by the above parameters.

PlainBill

[Davi.p]

Re: Benq T701 and unknown fet's smd code

Ok thanks for the help, sorry i was following soccer matches . I forgot to say that my level is very poor, so i've done the measurements, but for current i can't measure for now cause my tester ins't able, i will try to find datasheet for the panel so i don't have to measure.. (?) and second.. what do you mean for power bus?
Did you mean one of the output of the power supply board? The package is sot23...
Now i've found that the source of fet is connected with the 5v pin/rail out of p. supply,
the gate is 3,3v in st.by and 0,7xx volt in power-on..

[PlainBill]

Re: Benq T701 and unknown fet's smd code

Ok thanks for the help, sorry i was following soccer matches . I forgot to say that my level is very poor, so i've done the measurements, but for current i can't measure for now cause my tester ins't able, i will try to find datasheet for the panel so i don't have to measure.. (?) and second.. what do you mean for power bus?
Did you mean one of the output of the power supply board? The package is sot23...
Now i've found that the source of fet is connected with the 5v pin/rail out of p. supply,
the gate is 3,3v in st.by and 0,7xx volt in power-on..

Soccer, huh? I prefer American football; a game where you can go to the bathroom, then get a beer, without missing any action.

Heck, you have done most of the hard work already!!! I would have guessed the panel itself takes less than 2 amps - many have a 2 amp fuse.

NOW the problem. I can never keep 'n-channel vs p-channel' and 'enhancement mode vs depletion mode' straight in my mind, so you are going to have to figure out what combination you need.

It would also be a good idea to try a 'test run' with a 2-3 Amp (or even a jumper wire) from the source to drain pads for that transistor. I can't help thinking that SOMETHING caused the current surge that blew that transistor, and it would be a good idea to make sure the panel is working.

PlainBill

[Davi.p]

Re: Benq T701 and unknown fet's smd code

I add, from the datasheet the panel input current is 0,4/0,52max, but it say about
a 'rush current' of 2A/3Amax..

[Davi.p]

Re: Benq T701 and unknown fet's smd code

Soccer, huh? I prefer American football; a game where you can go to the bathroom, then get a beer, without missing any action.

But i live in Italy, there's no Am. football and soccer is a very technical sport..

Heck, you have done most of the hard work already!!!

If you say so.. don't seems to me..

NOW the problem. I can never keep 'n-channel vs p-channel' and 'enhancement mode vs depletion mode' straight in my mind, so you are going to have to figure out what combination you need.

Here i'm totally unable .. what to do? datasheet te only way?

It would also be a good idea to try a 'test run' with a 2-3 Amp (or even a jumper wire) from the source to drain pads for that transistor. I can't help thinking that SOMETHING caused the current surge that blew that transistor, and it would be a good idea to make sure the panel is working.

"2-3 Amp"...? Fuse? So for me has much sense to provide a new transistor
hope to find at least npn or pnp and try with this, or with a fuse i can't make damage to panel and is better...?

thks

[Davi.p]

Re: Benq T701 and unknown fet's smd code

One moment, you have told about the tests that i've made, but the meaning of them?
You don't saw nothing about the results that i've posted.. after, in base of the gate levels i saw you aren't able to determine npn/pnp? What changes if i use an NPN or PNP? At least it doesn't switch? If the p. supply 5v rail functions and is directly connected to the fet, the gate seems to function, the problem can be in a short on the circuit panel only? Or what?

[Davi.p]

Re: Benq T701 and unknown fet's smd code

I have taken the risk, i have put a very little piece of wire (a filament, to hope he act like a fuse..) fixed with ades. tape, i powerd up and i could see the logo and no signal
message.. so from my ignorance i think the panel is ok (obvious) and the only part faulty of the v.board is the fet.. now with wich i can swap it?