Benq fp71g+ dead. No light no signs. Capacitors look alright

[nicoursi]

Hello to everyone!
My father's monitor started to blink and my father used a toothpick to keep the two middle buttons pushed together (right arrow and left arrow). This temporarly solved the problem. My father was able to use the monitor with no problems for a month or two.

One day the monitor stopped working. Now it is not possible to start it, no led, no light no signs of life.

I opened it and i see no signs of bad capacitors. Everything looks fine.
The big capacitor (450v, 100 uF) though, even if it is not bulged or anything. it is a bit dirty, a slight black dirt I can rub off with my finger. Also the metal board lid is dirty in proximity of the capacitor. I don't know if this is normal due to the heat or if it could be a sign of bad capacitor.

Does anybody have any idea of what it could be and where shoul I look for a solution?

thank you very much!
Picture of the board attached. If you need some more picture plese tell me.

Nicola

[Trune]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Have you done any tests on fuses etc?

Just copying advice I was given but first of all test fuses.

The guys here will need a clearer picture so they can read the white writing also.

The board looks really odd about the ground cable, it looks warped, or it that just the pic?

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

i hope these picture are better.
i tested the fuse with the multimeter and it beeps.
Nicola

[Trune]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

This is the advice I got first off on mine.

Please be very careful doing the tests with power connected though, very careful and only if you are confident.

Selldoor:
When you measure anything you need to tell us what result you got. Anyway first can you test the voltage on the big cap.
CAREFULLY. as this is high voltage. Put your meter on 600vdc and put black probe on
negative leg and red on positive.

As a starter for things to test this is good - start at post19
https://www.badcaps.net/forum/showthread.php?t=10419


Also search the numbers of the chips on the heatsink and tests any mosfets, I think it will be the one to the right.

Rtech:

You also need to check the mosfet on the heatsink,this may help if necessary...
http://www.4qdtec.com/mostest.html
or you can measure between its pins and you do not want a short cct .


That should get you started and someone more knowledgable should advice after your responses.

[retiredcaps]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

i tested the fuse with the multimeter and it beeps.

You know there is more than one fuse on the board?

FP801 is a fuse too.

A good fuse will measure less than 1.0 ohms.

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Thanks guys for your help!
I didn't know there were more than one fuse

So, the following are the tests I run so long:
1. F601 and FP801 they both mesure 0.4 ohm
2. Big capacitor tested with power on with black(COM) on negative leg: 316 V.
3. Mosfet Q601. With Black probe(COM) on pin 1 and red on pin 2 (or pin 3) I always get 1ohm. With black on pin 2 and red on pi 3 i get a big number for a second and then 1 ohm again.
4. I couldn't check the other mosfet yet (IC601) because it has more that 3 pins and I have to do some more research .

Is the big cap reading ok?
Shoud i unsolder the mosfet Q601?

Thank you very much for guidance!

[Rtech]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Are you getting confused ????? is Q301 the one on the heatsink ?? and if so that IS the
Mosfet ??? and your measurements indicate that it is short circuit and needs taking out and confirming.I ask because the initial photo is so out of focus, you cannot read the component numbers !! IF it is the Mosfet that is faulty, then it may well be that other components have failed also,so a replacement should not be fitted until other tests have been carried out.

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Are you getting confused ????? is Q301 the one on the heatsink ?? and if so that IS the
Mosfet ??? and your measurements indicate that it is short circuit and needs taking out and confirming.I ask because the initial photo is so out of focus, you cannot read the component numbers !! IF it is the Mosfet that is faulty, then it may well be that other components have failed also,so a replacement should not be fitted until other tests have been carried out.

Sorry it is Q601 (not Q301). Yes, it is the one with the heatsink. Its is the mosfet. Sorry for confusion

What other tests do you suggest? Thank you!

[Rtech]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Mosfet out..and test as you did before to confirm resistance...OR you can do this:-
http://www.4qdtec.com/mostest.html
Lets do this first before thinking of other tests...also some good Focused photos from the top of the board, will help if we have to look at other components.

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Here better pictures.
I will do the tests later and post results.

[jetadm123]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

At the bottom of your first photo, I notice that the lead of the large resistor R607 is bent over and may be touching the lead of resistor R603?

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

At the bottom of your first photo, I notice that the lead of the large resistor R607 is bent over and may be touching the lead of resistor R603?

Yes it is bent over but it does not touch anything. Is it safe to bend components straight back or is it better to leave them as they are? I found many bent components on this board, is it normal?


I tested also IC702 (between the two heatsinks) and it behaves very similar, so theoretically faulty. But I am starting to think if I am doing something wrong. The pins of IC702 are not numbered but they have letters: R, A, K. I tested black on R, red on A first and on K second. Later A black and K red. K returns 1 with whatever pin. Looking at the back of the board I noticed that the soldering of IC602 touches the soldering of the pin K of IC702. Could it be the reason why it does not return anythink with the multimeter? If so, why the monitor has worked for years?

I still have difficulties in testing IC601 and IC 602 as they have, respectively, 8 pins and 4 pins.

IC601 part number is: 1200AP40 CPBJ 0633G. On the net i found this PDF: http://www.datasheetarchive.com/1200AP40-datasheet.html but the values reported for each pin are: 1 Adj, 2 FB, 3 CS, 4 Gnd, 5 Drv, 6VCC, 7 NC, 8 HV. So, which ones are the Source and the Drain?

IC602 part number is:40633 817A X
I couldn't find any info on the net. It has 4 pins and I do not know how to test it.

Thanks!

[selldoor]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

1200AP40

Do not test unless you know what you are doing HIGH VOLTAGE 450v.

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

1200AP40

Do not test unless you know what you are doing HIGH VOLTAGE 450v.

We are talking about testing for shorted transistors "in circuit", with power off and unplugged. So no harm possible bro'

[selldoor]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Ok - well in that case - knock yourself out.
IC602 may be one of these - - Cant actually see it on the picture www.alltronics.com/cgi-bin/item/817A/704/
They dont often fail.

Your priority should be getting Q601 out and checking it - actually looks burnt in the picture - try and get the part number off it before you remove in case it crumbles.

[Rtech]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

IC601 the 1200AP40 CPBJ is the SMPS chip that drives Q601,which we know is the mosfet.SO you must take Q601 out first and test.

[jetadm123]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Yes it is bent over but it does not touch anything. Is it safe to bend components straight back or is it better to leave them as they are? I found many bent components on this board, is it normal?

For the large resistor, it is not normal to have it bent over that far. The rest of the parts you can generally leave alone.

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Guys, i didn't manage to unsolder the Mosfet I cannot melt the solder. I tried to unsolder caps and other componens on a scrap board and it worked normally.

Can it be due to the heatsink sucking all the heat? Shoud I remove the heatsink first or do u know any trick to do it?

Sorry but I am a beginner here
Thanks for all inputs,
Nicola

[selldoor]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Preheat the board with a hairdrier or fan heater
Try and add some leaded solder to the solder you are trying to melt.

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Thanks! Adding some leaded solder to the solder I was trying to melt did the trick! But the question now is: is the heat sink glued to the board? I sucked up the solder with a pump but the heatsink looks like glued. Is that right? Just to know how I should proceed.

Sorry for my incompetence, but slowly slowly I will get there! I'm just trying to avoid damage

Thanks again!