Benq FP767 PS caps

[splaz]

The monitor had started to turn off every now and then for no reason, I actually thought at the time maybe it was video card related as I'd mucked around with drivers for it only recently.

Then the screen though would spend the majority of the time off and would only every now and then turn on... until over the last few days it wouldn't turn on at all... maybe a bit of blinking from the led and that's about it.

Opened her up and took out the power supply board, 2 bulged caps.



The brown one is a 1000uF/35v Elite.

Black one is a 1000uF/16v Elite.


Probably from different series, there are two more of the brown caps, look intact to me but I'll replace them as a precaution, same goes for another of the black cap.

There are a few Lelons on the board, I know they're known to be bad but none appear in anyway to be comprised I guess you'd say. Besides I don't have the right values to easily replace them with quality caps... to give you an idea, if I went to a local supplier... they'd sell me Lelon.

So they'll stay for now.

From my parts stash I'll use 1000uF/35v Panasonic FM to replace them, see if that fixes things. If not, might have to investigate further.

[Krankshaft]

Re: Benq FP767 PS caps

A great majority of the time the failure you describe will be remedied by capacitor replacement.

My HP 1955 (Benq build) that I repaired for myself (and that I'm using now) had Elites on it they were ok (monitor had a shorted inverter transistor and a shorted On/Off MOSFET) but I replaced them anyways with Panasonic FCs so that I wouldn't have to work on it twice.

To tell you the truth I haven't come across a single inverter board that I couldn't fix.

They are WAYYY simpler then ATX PSUs .

[splaz]

Re: Benq FP767 PS caps

Success.

Monitor is now working fine. I replaced two Elite brand I found that had vents, 470uF/16v off the top of my head with 470uF/35V Panasonic FM. There were smaller ones all over the place but didn't seem worth the effort to go all out.

I'd have some recap pics but the camera's battery is flat...

Oh and thanks again Krankshaft, you're quite the source of information.

[maverick530]

Re: Benq FP767 PS caps

I have the exact same problem with my BenQ-built HP 1955 Power Inverter Board. The monitor does not power on at all.

Below are two pictures of my board. Notice the two burned marks on the board that I've circled in white.

I've done a bit of research on this forum already and have come across a few threads that are helpful:

https://www.badcaps.net/forum/showthread.php?t=5031
https://www.badcaps.net/forum/showthread.php?t=6374

However, I'm new at this--so far my experience with fixing monitors has been limited to swapping parts, but now I want & need to actually FIX these boards as nobody sells working power boards.

My biggest question is, you say you've never come across a board like this that can't be fixed, but can this type of problem really be fixed without having to do any work on the under side of the board?
It seems like replacing anything on the back of the board is impossible since the parts are so small and practically "printed" onto the board.
Same thing goes for the PCB's themselves. What if there is a problem INSIDE the printed circuit board?

Lastly, can someone show me (by circling on my picture) what exactly would need to be replaced? A picture speaks a thousand words. Thanks so much in advance,

[Bobdee]

Re: Benq FP767 PS caps

Looks like you have been overlooked here Maverick, dont know why,
Post and let us know if you havent fixed problem, you probably wont have to touch those small components on underside of board to fix this one

[maverick530]

Re: Benq FP767 PS caps

I still haven't fixed the problem; I haven't touched the board since I received no posts. That is encouraging that you think I won't have to touch the back of the board, but I'm still not positive where to begin.

[EGuevarae]

Re: Benq FP767 PS caps

Looks like you have been overlooked here Maverick, dont know why,
Post and let us know if you havent fixed problem, you probably wont have to touch those small components on underside of board to fix this one

I didn't see this one. I normally browse only the Computer Display area.
Well, there's not a single cap bulged in the picture (as far as I can see), so either you replaced them already, they are OK, or at least they LOOK ok.
First thing first : Are you getting any AC input (fuse in the yellow/red square is not open)
Also, check if you can get voltage readings in the pico fuse (yellow) and in the bridge that should have been a pico fuse too. If the caps are all the originally installed, post the info on them, just so the info can be referred too for later reference.

[kc8adu]

Re: Benq FP767 PS caps

moved to get better exposure.
just do the usuall benq fix.
5706/7's, fu9624,solderjoints on transformers,open fuses,and lets not forget bad caps.

[EGuevarae]

Re: Benq FP767 PS caps

moved to get better exposure.
just do the usuall benq fix.
5706/7's, fu9624,solderjoints on transformers,open fuses,and lets not forget bad caps.

Never ran into that board so far. So, this is a must for these boards (I mean, standard practice when they fail)?
And thanks for moving it.

[Bobdee]

Re: Benq FP767 PS caps

Never ran into that board so far. So, this is a must for these boards (I mean, standard practice when they fail)?
And thanks for moving it.

Hello Eduardo,
Kc suggestions are the run of the mill with these Benq boards, they are used in Benq,Dells and HPs among others, same problem all over Badcaps Forum
But Maverick does say he has no power at all,
Suggesting, P/S is faulty this time,
looking at his board he probably needs inverter overhaul as KC suggests also

[PlainBill]

Re: Benq FP767 PS caps

I still haven't fixed the problem; I haven't touched the board since I received no posts. That is encouraging that you think I won't have to touch the back of the board, but I'm still not positive where to begin.

I'd like to help, but need more information. First of all, a picture of the back of the board would be helpful. I'd like to see what caused those two hot spots on the board.

The second piece of information is what is your level of experience? And what equipment do you have available? A DVM, soldering iron, and wire cutters are the minimum tools required.

A first step is to use a DVM and Carefully! check the voltage across C605 with the power cord plugged in and the power switch on.

PlainBill

[EGuevarae]

Re: Benq FP767 PS caps

Hello Eduardo,
Kc suggestions are the run of the mill with these Benq boards, they are used in Benq,Dells and HPs among others, same problem all over Badcaps Forum
But Maverick does say he has no power at all,
Suggesting, P/S is faulty this time,
looking at his board he probably needs inverter overhaul as KC suggests also

That't the reason I asked, as I've seen this suggestion all over the forums. I just wanted to get a confirmation from him, you, or someone that was answering directly to me.

I'd like to help, but need more information. First of all, a picture of the back of the board would be helpful. I'd like to see what caused those two hot spots on the board.

I was thinking of the brown spots under the jumpers too. I just want to have info available in case I get one of these ...

[maverick530]

Re: Benq FP767 PS caps

Here are the caps on this HP 1955 benQ power board, generally from left to right:

2x 220uF black 35V Elite
2x 33uF 50v TK?
1x 150uF 450V Elite (big black one)
4x 1000uF 16V Elite (brown)
2x 1000uF 10v Lelon (green)
2x 47uF 50v green Lelon (smaller, bottom of board)

[maverick530]

Re: Benq FP767 PS caps

I'd like to help, but need more information. First of all, a picture of the back of the board would be helpful. I'd like to see what caused those two hot spots on the board.
PlainBill

Here's a picture of the back of the board. I can't see any burns on this side of the board, but this should help to see what might have caused the burns on the front side.

The second piece of information is what is your level of experience? And what equipment do you have available? A DVM, soldering iron, and wire cutters are the minimum tools required.
PlainBill

I'm new at this, but really want to learn. I'm ok with messing up a few boards in the pursuit of learning how to fix these. I have access to a DVM, soldering iron (I need to get a hotter iron, and a better tip--any suggs where to go?) and wire cutters, yes.

A first step is to use a DVM and Carefully! check the voltage across C605 with the power cord plugged in and the power switch on.
PlainBill

Hope to test the power to this board as suggested this weekend.

[PlainBill]

Re: Benq FP767 PS caps

Here's a picture of the back of the board. I can't see any burns on this side of the board, but this should help to see what might have caused the burns on the front side.

Hope to test the power to this board as suggested this weekend.

Huh!!! It looks like the heat was caused by the smd resistors in that area.

You might take a look at IC701 on the back; that doesn't look healthy. And as an item of curiosity, what are the numbers on the 16 pin IC on the back of the board?

PlainBill

[maverick530]

Re: Benq FP767 PS caps

Huh!!! It looks like the heat was caused by the smd resistors in that area.

You might take a look at IC701 on the back; that doesn't look healthy. And as an item of curiosity, what are the numbers on the 16 pin IC on the back of the board?

PlainBill

You're right, that IC701 doesn't look healthy--half of it has a shiny luster and the other half doesn't. Then again, most of the larger ICs on the back look that way, although not as bad.

The 16 pin IC on the top of the back of the board says:
5ICLZVK
TL1451A

It looks like the burn marks correspond to these little tiny resistors? on the back that say "471" on them. They're so tiny though, I better not have to replace them!

[maverick530]

Re: Benq FP767 PS caps

Ok, I'm still trying to locate all of the possible bad parts mentioned:

I've labeled the C5707s and the TRANSFORMERS and FUSE (is this correct?)

Can someone please circle where the MOSFET or TRANSISTORS would be on this board?

I just want to make sure I'm looking at the right parts, and my terminology is correct; remember, I'm new at this.

[PlainBill]

Re: Benq FP767 PS caps

Ok, I'm still trying to locate all of the possible bad parts mentioned:

I've labeled the C5707s and the TRANSFORMERS and FUSE (is this correct?)

Can someone please circle where the MOSFET or TRANSISTORS would be on this board?

I just want to make sure I'm looking at the right parts, and my terminology is correct; remember, I'm new at this.

Your labels are accurate, but incomplete. I'm going to walk you through this board; I'll be skipping a few parts. Feel free to ask questions if you need more information.

AC power comes in through the power connector, goes through the switch and the fuse, F601. L602 and the caps on either side are there to block surges. TR?601 (the green blob ) is there to reduce inrush current when the power is turned on. Directly above L602 is a bridge rectifier; it converts the AC to DC. 120 VAC in gives about 165 VDC across the legs of C605 - the 150 uF, 450V capacitor. One of the first steps is to measure the voltage across C605 With everything hooked up and the power switched on. If it's around 165 volts F601 is good.

The next item of interest is IC601 in the blue circle. That controls the conversion of 165 VDC to 12 VDC and 5 VDC. Immediately to the left of IC601 is C611; above IC601 and slightly to the right is another capacitor, C608? Those are important because they form the power supply for IC601.

The power mosfet is the device in the green circle. That switches the power to T601. If F601 is open odds are either the bridge (BR601?) or the power mosfet are shorted.

The output of T601 is converted to DC by the diodes mounted on the heatsink I marked with a brown X. To the right of them in the brown circle are 6 capacitors that filter the output from the diodes. And next to that is the cable connected too the logic board.

In the white circle to the left of the heat sink is another fuse, PF701. That is in the power supply to the inverter.

I prefer a 'divide and conquer' troubleshooting approach. If you get 165 volts across C605 we know the AC input side is good. The next step would be to measure the voltages on the cable to the logic board. If several of them read 5V and 12V we know the power supply is working. If not, suspect C611 and C608?.

If the power supply seems to be working, check the voltage on both sides of PF701 (or check it's resistance with the power off).

PlainBill

[Bobdee]

Re: Benq FP767 PS caps

sorry messed up

[jpdoe]

Re: Benq FP767 PS caps

Great walkthrough, PlainBill.

I've always wondered which is the easiest way to test the bridge rectifier.
From reading these forums, I've gathered that it's a good idea to desolder one terminal of a diode in order to test the bridge.
If we number the diodes on the next figure from 1 to 4, from top to bottom, which terminal should I desolder?

Thanks