@retiredcaps: I installed caps that I had taken out prior to taking the picture and the monitor works. Is it better to replace now or wait till it messes up again?
Is it better to replace now or wait till it messes up again?
Most here would recommend replacing them now. I have no strong opinion either way. If this were a bigger monitor or LCD/plamsa TV, I would suggest replacing the caps now.
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Most here would recommend replacing them now. I have no strong opinion either way. If this were a bigger monitor or LCD/plamsa TV, I would suggest replacing the caps now.
THanks alot for your help, bro. This forum and its people rock.
I've a Dell E173FPc (dunno why all of the diffrnt variants), with the dreaded "power on" for 2 sec. then screen goes blank, but the power button stays lit at a steady green. Scouring the 'net for possible solutions, I found many. I did buy the four trannies and replaced them (2C5707 originals). All kinds of excited, I put this monitor back together soooo fast there was, I say, there was smoke a comin' off my fingers! Thinking to myself, "Wow, that was so easy can't wait to see this baby fire up!" Then, just as I was preparing to snap the back cover onto the front bezel, a voice from above echoed down (only I could hear), "Whoa fella, don't you think you ought to plug this bad chicken back in and test it before you go through the trouble of the plastic clip BS?". To which I replied (to myself), "Maybe I ought to plug in....". Well don't you know...same shiite as before. Hmmm, what the blue blazes could the problem be?
Sitting there bewildered, no joy, I went back to the 'net. Start searching. Finally found this forum (Interesting star of a discussion forum, the humble capacitor), and finally this thread. I read through the first few posts, all very informative. "Bad Caps!", they shouted. "No try the four transistors prone to failure!". Still yet, "What about the transformer, mine's was busted!". More over "Heat! Heat is the real culprit!". That got me thinking.
So I break out my jeweler's loupe, shift down into inspection gear, and really start scrutinizing the area between the two backlight transformers where the four transistors live. First observation, the board does have some discoloration in the immediate area. Flip board over (because I know full well where the problem is), and begin to look at EACH and every solder joint in the vicinity. Second observation, a few solder joints at both backlight transformers seem to have the telltale cold solder joint, looking closely you can see a minute "ring" around the posts. Could this be the result of extreme heat cycling? I'll leave that for discussion, although my theory at this point is a combination of bad soldering and heat cycling (which isn't a flame on two wheels).
What worked for me was to reflow the solder at any point that looked suspect (especially the pins for the transformers, two on the one side, and about 6 or 7 on the opposite side). After I was satisfied that everything was kosher, I began to reassemble the monitor (up to the point of reattaching the rear cover) and test. Joy at last! My hopes are that BenQ was having a bad week of soldering and not the heat stress. Only time will tell.
Hope this helps
If you voted for Obama in 2008 to prove you weren't a racist, you'd better vote for someone else in 2012 to prove you're not an idiot!
(up to the point of reattaching the rear cover) and test. Joy at last! My hopes are that BenQ was having a bad week of soldering and not the heat stress. Only time will tell.
Hope this helps
Congrats on the successful fix. Fun isn't it?
If you've read the many threads, the bad solder joints are the the root of many of the problems with this model.
My attack plan for this model and variants is, recap, re-solder the transformers and any questionable joints test the 5707 transistors the FETs and pico fuse.
If I find a shorted transistor, I replace 'em in pairs, then power up and test.
I don't shotgun parts in ('cept caps, I ALWAYS recap) just replace failed parts, and their partners.
There's a good technical description in one of the threads somewhere about how the bad joints cause the 5707s to fail, which sometimes blows the pico fuse.
36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....
I have two different model BenQ monitors. Both have blown 3Amp fuses and both were full of cold solder joints so the manufacturer was having much more that one bad day. Both are now working again. What I want to know is why there is an inverter circuit in the monitors in the first place. These monitors are designed to plug into the mains. They have a ready supply of AC voltage just waiting to be transformed into whatever voltage the backlights require. Why rectify the AC to DC and then invert the DC back to AC? Maybe there is a reason but I can't think what it would be. Any suggestions?
I have two different model BenQ monitors. Both have blown 3Amp fuses and both were full of cold solder joints so the manufacturer was having much more that one bad day. Both are now working again. What I want to know is why there is an inverter circuit in the monitors in the first place. These monitors are designed to plug into the mains. They have a ready supply of AC voltage just waiting to be transformed into whatever voltage the backlights require. Why rectify the AC to DC and then invert the DC back to AC? Maybe there is a reason but I can't think what it would be. Any suggestions?
Yeah, the engineers who build LCDs are brighter than you.
The inverter does much more than boost the voltage. It is a constant current AC source with current limiting and over voltage protection.
The efficiency of a transformer depends on it's frequency. A transformer to step 120 VAC, 60 Hz up to 1200 Volts would weigh several pounds. Also, the AC input voltage can vary from as low as 90 volts to about 250 volts. That complicates the design significantly.
PlainBill
For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.
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I have a Dell 173fpb and a Dell 153fpb that both have the same problem, I have replaced the 6 transistors and the fuse on both, and now when I power them up, the secondary pin on one of the inverter transformers short to the ground pin, on both monitors. I have tried disconnecting the leads to the lamps of the display and they still smoke. Is this indicative of shorted transformers? Here is a picture to help explain the issue, but it isn't the best quality...
I have a Dell 173fpb and a Dell 153fpb that both have the same problem, I have replaced the 6 transistors and the fuse on both, and now when I power them up, the secondary pin on one of the inverter transformers short to the ground pin, on both monitors. I have tried disconnecting the leads to the lamps of the display and they still smoke. Is this indicative of shorted transformers? Here is a picture to help explain the issue, but it isn't the best quality...
What do you mean ' the secondary pin on one of the inverter transformers short to the ground pin'? Are you saying an arc forms between the secondary pin and the ground pin?
You DO realize that the inverter is a constant current AC source. If the CCFL is disconnected (or a wire to the CCFL is broken, or the CCFL is broken), the inverter will ramp the voltage up for a few seconds until the OVP (Over Voltage Protection) shuts the inverter down. Once an arc forms, the epoxy resin in the PC board breaks down and is carbonized. The carbonized material is conductive, and you have a self-repairing flaming resistor formed. It's not a great accomplishment, it's been done by many people, some of them brighter than you.
Considering the demand for 15" LCDs, it's barely worth repairing them. HOWEVER, if you want to give it a try, scrape away ALL of the charred material between the two pins. If you have a Dremel rotary tool (or equivalent), I would cut a slot in the PC board between the two pins. Do this CAREFULLY. On slip and you may destroy the transformer.
PlainBill
For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.
I have the same symptoms with the E173FPb, did the transistor swapouts, and it worked a little while, but then it went to the white flashing screen with the green blinking power light, however I noticed it did this when the monitor was cold. I remember when growing up in Idaho, when it was 30 degrees, the shop lights in the garage (which were flourescent) struggled to light up when it was that cold. I think that's what's going on with this monitor. It doesn't ionize and light up and that throws the inverter board into a tailspin.
I tore down the LCD and found the top CCFL Tube had a very black end, reminiscent of a worn out flourescent lighting tube.
I had an extra LCD from a Mag 17" that had the same symptoms, and it had the same Optronics LCD and CCFL leads. One of those CCFL tubes was cracked at the end and useless, however the other was "ok", I installed this one and so far so good. However in the end, I believe CCFL's are wearing out because these monitors are very old. When I visit my used electronics parts store I see numerous 2003-2005 circa Flat Screens in the "as is" $10 pile, I know now to pass on them, I don't know if you can buy raw CCFL tubes - installing used ones from an equally old monitor is a crap shoot. The whole reason they're there in the junk pile is probably because they've led a long hard life. Time to upgrade to a LED Flat Screen.
This is one modification that backlightnya LCD monitor died and I replaced it with the LED on the bottom of the LCD as many as 12 pieces of LED and relay install + Bc109 as LED driver.
Google is your friend.
PlainBill
For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.
When I visit my used electronics parts store I see numerous 2003-2005 circa Flat Screens in the "as is" $10 pile, I know now to pass on them,
It depends. Monitors can die from a number of things including bad caps, dodgy soldering, overheated transistors, bad fuse, etc. If the monitor dies "early", then the ccfls could be in very good condition.
I don't know if you can buy raw CCFL tubes - installing used ones from an equally old monitor is a crap shoot.
ccflwarehouse.com, ccfldirect.com, and ebay have sell bare ccfl tubes.
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