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Old 05-06-2010, 10:22 AM   #1
retiredcaps
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Default Benq Q7T4 (FP71G) solder joints

I picked up a Benq FP71G and the previous owner said the monitor would stay on for 15 to 20 minutes and then shut down.

I took it apart and noticed no obvious bulging caps, but when I looked at the other side, I noticed 3 possible issues and would like comments on what I found.

1) C826 solder joint is fused/touching the middle lead/pin of Q809. I don't think it should be touching. The other C826 joint is NOT fused with Q808 (mirror side). Should I unfuse this so they are not touching?

2) T601 lead/pin 7 has no solder whatsoever. It is perfectly clean like it was either purposely not soldered at manufacturing or totally missed by mistake? Should T601 pin 7 be soldered?

3) There is discoloration in the solder on some of the pins/leads on most of the transformers. See T801 for an example. Is this bad solder and should I retouch? The spacing is very tight and I don't want to unless I absolutely have to.

I'm surprised the monitor even works (I powered it up and got a picture, but shut it down to avoid further damage).
Attached Images
File Type: jpg no-solder.jpg (120.8 KB, 128 views)
File Type: jpg joined-solder.jpg (149.9 KB, 131 views)
File Type: jpg bad-solder1.jpg (116.9 KB, 124 views)
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Old 05-06-2010, 12:17 PM   #2
smason
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Default Re: Benq Q7T4 (FP71G) solder joints

1) It looks like the circuit board trace goes there anyway, so likely not a problem. You could remove solder to confirm I suppose.

2) There's no pad to solder to, so it's likely an unused pin, the hole just there to allow the part to fit, save having to clip it off.

3) I'd say that's just evidence that someone has re-soldered those joints, and didn't remove the flux.
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Old 05-06-2010, 01:29 PM   #3
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Default Re: Benq Q7T4 (FP71G) solder joints

Quote:
Originally Posted by smason
1) It looks like the circuit board trace goes there anyway, so likely not a problem. You could remove solder to confirm I suppose.

2) There's no pad to solder to, so it's likely an unused pin, the hole just there to allow the part to fit, save having to clip it off.

3) I'd say that's just evidence that someone has re-soldered those joints, and didn't remove the flux.
1. I agree, it's supposed to go there. I wouldn't even bother removing the excess solder.
2. Exactly right.
3. Correct, but incomplete. Resolder those pins. Benq monitors are notorious for bad solder joints on transformers. If you feel the pins are too close together, get a smaller soldering iron tip.

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Old 05-14-2010, 04:41 PM   #4
retiredcaps
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Default Re: Benq Q7T4 (FP71G) solder joints

Thanks for the feedback so far. I have been working on other LCD monitors so this one took a backseat (including a HP 22 inch - just waiting for new caps to arrive). I put the Benq all back together without doing anything (no new caps, no soldering) other than clean it up (vacuum, reseat all the connectors).

I wanted to see the 15-20 minute shutdown myself and maybe get more clues (like audible whining, hot spots, blinking lights, etc), but so far, the monitor has been running for 40 minutes and it is still working fine.

Of course, murphy's law will make this monitor shutdown as soon as I hit submit reply.

PS. PlainBill Good luck on the cataract surgery. Hope to see you back on these forums soon afterwards.

Quote:
Originally Posted by retiredcaps
I picked up a Benq FP71G and the previous owner said the monitor would stay on for 15 to 20 minutes and then shut down.
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Old 05-14-2010, 05:29 PM   #5
retiredcaps
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Default Re: Benq Q7T4 (FP71G) solder joints

Well, Murphy waited 27 minutes after my post before he showed up.

So the FP71G+ lasted 67 minutes and then the backlight went off. There was no smoke, no whining noises (using the high tech paper toilet roll), and no obvious hot spots on the back of the monitor.

When the backlight went off, the power LED was green solid (not blinking). If I turned off the monitor and turned it back on right away, the backlight would come on for about 1 second, but then turn off right away.

So I powered off the monitor and let it cool down for 5 minutes. Then I powered it back and it worked for about 11 minutes before the backlight went off again. Again, no hot spots, no audible whine, power LED on solid.

I have ordered a digital multimeter and 30x jewelers lens to help me look for those solder joints on the transformers and waiting for them to arrive from afar.

In the meantime, I going to use this Benq as much as I can to see if I can get something to obviously fail (like a bloated cap).

I have a little hand held fan that I'm going to use to see if that helps or not.

Quote:
Originally Posted by retiredcaps
Of course, murphy's law will make this monitor shutdown as soon as I hit submit reply.
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Old 05-15-2010, 07:55 AM   #6
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Default Re: Benq Q7T4 (FP71G) solder joints

This looks very similar problem that I'm having with my HP w20. I think my problem may be caused by high voltage capasitors.

http://www.badcaps.net/forum/showthread.php?t=9703
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Old 05-15-2010, 09:19 AM   #7
retiredcaps
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Default Re: Benq Q7T4 (FP71G) solder joints

I have been following your HP thread since the beginning because I just received a HP w22 a few days ago. I have not written about it on the forum yet because I'm waiting for parts to arrive, but my HP w22 has 2 obviously bloated su'scon 1000uF 10v caps.

I was going to post a "case study" with the HP monitor once it is fixed because it took a long time to take apart and you have to do it carefully.

I'll take a look at the high voltage capacitors in the BenQ.

Quote:
Originally Posted by CapBlown
This looks very similar problem that I'm having with my HP w20. I think my problem may be caused by high voltage capasitors.

http://www.badcaps.net/forum/showthread.php?t=9703
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Old 05-15-2010, 02:46 PM   #8
retiredcaps
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Default Re: Benq Q7T4 (FP71G) solder joints

I'm curious if you have tried lowering the contrast and brightness to see if that extends the time between shutdowns on the HP w20?

I lowered the brightness and contrast from 80/60 (from original owner) down to 25/35 and noticed my BenQ FP71G+ now stays on for 3.5+ hours (so far no unexpected black screens like before). I'm going to use these settings for a couple of days and see if the monitor stays on. Afterwards, I'm going to crank it up to 100/100 to see if the monitor shutdown frequently.

Once the jeweler's loupe arrives, I will probably touch up the soldering on the transformers and other suspect joints.

Quote:
Originally Posted by CapBlown
This looks very similar problem that I'm having with my HP w20. I think my problem may be caused by high voltage capasitors.

http://www.badcaps.net/forum/showthread.php?t=9703
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Old 05-15-2010, 11:19 PM   #9
CapBlown
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Default Re: Benq Q7T4 (FP71G) solder joints

Quote:
Originally Posted by retiredcaps
I'm curious if you have tried lowering the contrast and brightness to see if that extends the time between shutdowns on the HP w20?
Yes I tried that too. Factory defaults give 90% brightness with HP, which was set when I got the monitor. It was a bit too bright for me so I reduced it first to 50 and then to 20 for testing. Monitor stayed on longer, maybe 25-35 minutes. But when I removed backpanel and that metallic casing inside, I got it running even 4 hours before going dark.
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