BenQ FP71G+S (No, it's not just the backlight)

[c_hegge]

No, it's NOT just the backlight this time. When I turn it on, it says on for about 1 or 2 seconds and powers off again completely (the power light also turns off). Upon opening it I noticed what looks like some heat discolouration around the bottom left corner of the first pic. The transistor on the other side (IC701) doesn't look fried, although I can't read the markings on it. It looks like there is a coat of flux on it, which I cleaned off. Markings are L117 33 KDF6520 (
hard to tell. Could also be KOF6520). The caps are all Elite, except for a few small 100uF 25V Jamicons and two light green 1000uF 10V Lelons.

What do you guys think? Caps? or something else?

[el3ctroded]

Re: BenQ FP71G+S (No, it's not just the backlight)

Have you tried testing for shorts on the part that got hot?

[retiredcaps]

Re: BenQ FP71G+S (No, it's not just the backlight)

I bet the L117 33 is a voltage regulator that outputs 3.3V DC. I only say this because of my recent finds with A1117 voltage regulators in my Daytek thread.

On both my FP71G+, I have the same discoloration from the same IC701 location.

Check (since you didn't say you did or not)

1) PF801. On mine, it it shorted.
2) Check c5707 transistors. I have 2 bad on mine.
3) Check FU9024N.

The transistor on the other side (IC701) doesn't look fried, although I can't read the markings on it. It looks like there is a coat of flux on it, which I cleaned off. Markings are L117 33 KDF6520 (hard to tell. Could also be KOF6520).

[c_hegge]

Re: BenQ FP71G+S (No, it's not just the backlight)

Have you tried testing for shorts on the part that got hot?

I did. it doesn't seem to be shorted.

1) PF801. On mine, it it shorted.
2) Check c5707 transistors. I have 2 bad on mine.
3) Check FU9024N.

1. Aren't fuses supposed to be shorted and only open when they blow?
2. Thanks. Will do.
3. Assuming you mean transistors Q812 and Q805, neither are shorted on this monitor

[PlainBill]

Re: BenQ FP71G+S (No, it's not just the backlight)

I agree with retiredcaps, that's a 3.3 volt regulator.

The fact that it does a total shutdown is significant. The first step would be to check the 5.5, 3.3, and 12 volts (if present) on the cable to the logic card. If they are still present and stable, the problem is PROBABLY on the logic card. If they disappear, look at the power supply board.

It goes without saying - replacing those Elite caps would be a very good idea. Also, check any voltage regulators on the logic card.

PlainBill

[retiredcaps]

Re: BenQ FP71G+S (No, it's not just the backlight)

Yes, sorry, I meant open. I should have just wrote, make sure the picofuse is 0.03ohms or less.

1. Aren't fuses supposed to be shorted and only open when they blow?

[c_hegge]

Re: BenQ FP71G+S (No, it's not just the backlight)

Retiredcaps, I checked the pico fuse and it seems fine

PlainBill, Do you know what voltages to expect on which pins? There is no cable for logic board, it plugs straight in to the power supply.

[PlainBill]

Re: BenQ FP71G+S (No, it's not just the backlight)

Retiredcaps, I checked the pico fuse and it seems fine

PlainBill, Do you know what voltages to expect on which pins? There is no cable for logic board, it plugs straight in to the power supply.

Look at the back of the board. There are 12 pins. 4 of them are obviously ground, two of them are not used. Two others are connected to thin traces; they are the control lines for the inverter. That leaves you with two sets of two. You had better be able to take it from there.

PlainBill

[retiredcaps]

Re: BenQ FP71G+S (No, it's not just the backlight)

Here is what I have on mine. I only measured the "even" pins because the "odd" numbered pins are hard to reach with the probes.

pin 2: 0.00V
pin 4: 0.00V
pin 6: 0.00V
pin 8: 5.23V
pin 10: 3.29V
pin 12: 3.25V

PlainBill, Do you know what voltages to expect on which pins?

[c_hegge]

Re: BenQ FP71G+S (No, it's not just the backlight)

Voltages are there, even after the shut down. Also, after it shuts down, you can power it back on immediately after, without unplugging the AC, but it will just shut off again. Looking like the logic board at this point.

[PlainBill]

Re: BenQ FP71G+S (No, it's not just the backlight)

Voltages are there, even after the shut down. Also, after it shuts down, you can power it back on immediately after, without unplugging the AC, but it will just shut off again. Looking like the logic board at this point.

That's what I would expect. I would carefully check the voltage regulators on the logic board.

PlainBill

[retiredcaps]

Re: BenQ FP71G+S (No, it's not just the backlight)

If it helps, on mine, I only see one obvious voltage regulator which is a 950T65. On pin 1, I get 3.3V DC and pin 3, I get 2.5V DC. pin 2 is GND.

I would carefully check the voltage regulators on the logic board.
PlainBill

[c_hegge]

Re: BenQ FP71G+S (No, it's not just the backlight)

I did a resistance test between the pins. It doesn't seem to be shorted. I got another monitor cheap, so I'm not all that worried over it anymore. I'll try re-capping the Power supply with pannies. If it doesn't help, I'll get rid of it.

[retiredcaps]

Re: BenQ FP71G+S (No, it's not just the backlight)

Before you recap, check the voltage on the regulator. I'm not 100% sure, but a resistance test may not be sufficient.

It may not be shorted, but it may not put out 2.5V DC.

I did a resistance test between the pins. It doesn't seem to be shorted.

[georugby]

Re: BenQ FP71G+S (No, it's not just the backlight)

No, it's NOT just the backlight this time. When I turn it on, it says on for about 1 or 2 seconds and powers off again completely (the power light also turns off). Upon opening it I noticed what looks like some heat discolouration around the bottom left corner of the first pic. The transistor on the other side (IC701) doesn't look fried, although I can't read the markings on it. It looks like there is a coat of flux on it, which I cleaned off. Markings are L117 33 KDF6520 (
hard to tell. Could also be KOF6520). The caps are all Elite, except for a few small 100uF 25V Jamicons and two light green 1000uF 10V Lelons.

What do you guys think? Caps? or something else?

Damn! It looks like the same card I have in my hands right now! I'll get through the problem with all your infos and input. I'll come back to give you what happened or if I'm still searching!

Great forum! Great people!!

Cheers!!

Jeff

[georugby]

Re: BenQ FP71G+S (No, it's not just the backlight)

Jeez, forgot to ask, how do I check the backlights?

Thanks in advance!

Jeff

[Dumah Brazorf]

Re: BenQ FP71G+S (No, it's not just the backlight)

Change the transistors of the backlights, 4+2.
Even if they seems good with the diode test they probably have ad higher hfe draining more current and causing the logic to shutdown.
You can find a kit on ebay.