Re: Dell E172fpb
It would be fantastic if someone could find a copy of the workshop manual for these little buggers - what we could achieve with a decent circuit diagram would be beyond belief.
dockarl
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Last Activity: 08-17-2006, 07:21 PM
Joined: 07-03-2006
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Re: Dell E172fpb
Hmm..
You are all suceeding in scaring me that my repairs may be temporary, which would be a great shame as one of the fantastic things about this monitor is you can whip out the stand screws, turn it 90 degrees, rip of the metal tap on the display stand and (albeit using only the top two screws to mount it) use it in portrait format instead of landscape (if you have a graphics card that allows that). At the moment I have one widescreen running on my vid card digital output (for viewing webpages etc) and the 'repaired' one running in portrait mode...Leave a comment:
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Re: Dell E172fpb
Hi STJB!
Before you go buying another transformer it might be worthwhile making ABSOLUTELY CERTAIN that you installed the new transistors the same way as the old ones - and check the data sheets to DOUBLE CHECK that the E C and B for your transistor are aligned with those printed on the board.
Also, could be worth checking for continuity between the legs on the new transistors and their relative tracks, just in case you have a solder joint problem.
Mine still going strong ladies and gentlemen (at this stage)..
...Last edited by dockarl; 07-21-2006, 03:21 AM.Leave a comment:
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Re: Dell E172fpb
I must add - the transistors in question get BLOODY HOT - hotter than I would have thought would be usual, even given the large number of watts they are designed to handle. I've thought about adding a small fan etc - but that really begs the question - WHY ON EARTH should you need to go to these lengths to keep it cool? I reckon Benq has simply done a pretty shoddy job when it comes to design and reliability testing on this model, and I hope they've ironed the problems out now for their newer models.
DocLeave a comment:
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Re: Dell E172fpb
longempty, it's interesting that yours failed at just over one year old too - mine also - just out of warranty - now call me a cynic, but perhaps there is a 'bastard warranty expiry detector chip' somewhere in these things, along the same lines as the 'need to use urgently' detector chip built into consumer equipment such as photocopiers, the 'driver in a hurry' detector chip in traffic lights on the route to work, and the 'user has forgotten his battery charger' chip built into mobile phones to ensure the battery discharges at twice the normal rate when away from...Leave a comment:
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Re: Dell E172fpb
Yep - still working ok. One of the other (old) trannies I didn't replace went out in sympathy, causing the same old 'on for two seconds then off' (interestingly usually corrected for about 20 mins or so by unplugging the monitor, leaving off for 10 secs or so then plugging in and turning on again) so i ended up replacing the other two trans as well about a week ago - so far so good. Will update if anything else happens.
Could be worth considering whether or not to do away with the transistor control alltogether and just run the backlights at full...Leave a comment:
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Re: Dell E172fpb
Enkay78 -
I would firstly check the voltage at emitter and collector on all the transistors to check for any differences. If they look ok, I'd start to check the output of the four transformers (look back at about page 1 of this thread for the pictures to see the transformer Drexal is talking about) and check the output on all four.
Be VERY VERY careful when working with the live board.. there is mains potential on the board and I don't want to see you getting fried.
All the best,
DocLeave a comment:
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Re: Dell E172fpb
Drexal,
How is your fix with the transformer going? For the benefit of the other members having the same problem as you, what was the part number on the transformer and from your supplier?
Cheers,
DocLeave a comment:
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Re: Dell E172fpb
Hi Drexal!
Yep - over a week now and mine still working fine with MJE3055 NPN transistors - I will let you people know if any further problems - interested to hear your comments re: transformer - there always had to be a reason they were blowing.
Enkay - I have no idea what your issues would be - obvious one to check would be that polarity is right - the transistors should be replaced with the flat metal back facing the same way as the original if using the MJE3055 - pin for pin drop in replacement. Also check for solder bridges before...Leave a comment:
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Re: Dell E172fpb
I guess a positive of this finding is that (if this is replicated in other cases, which I assume it will be) removing and re-testing the 'dud' transistor pair out of circuit will allow people to replace the outer transistor (nearest to edge of board) with the 'false dud', and the inner transistor with the new (larger) replacement transistor.
Given the lower height of the original transistors, this will negate the necessity for hacksaw surgery to the casing to allow the transistor to fit as the outer one (where the case curves in) is the only one...Leave a comment:
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Re: Dell E172fpb
Hmm, I must humbly apologise - after these criticisms I have gone back and retested the two 'broken' transistors, as I only tested one yesterday. Out of circuit, one tests broken, the other tests ok - guessing that when testing in circuit, as these two transistors are tracked together, both appear broken.
Long and the short - I could have replaced only 1 - so a great new monitor for $1 - could be money for
(perhaps I should stop having so much of that before I hastily reply)
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Re: Dell E172fpb
I agree with rainbow, to an extent, but if you remove the 'shorted' transistors, you will find they test fine (unless it is another problem - rare from what I hear) transistors can easily test as 'shorted' if they are blown, simply because they then no longer act as valves - they simply let current through regardless of their settings. If you disagree with this rainbow, go right ahead. Rainbow contends this is not the case - reading back through rainbow's posts, I only see criticism - honestly, I am an instrumentation engineer and lecturer, trying to provide good...Leave a comment:
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Re: Dell E172fpb
short answer is, we are testing 'in circuit'..Leave a comment:
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Re: Dell E172fpb
if you have a matrix of diodes, essentially two transistors in parallel, as per this circuit, it is extremely easy for a bad solder joint to result in a short. Every time you start your computer, the board heats up, every time you shut it down, the board cools down... let's call it a 'cycle'. Different metals expand at different rates, hence, over time, the leads of the transistors will seperate from the solder that holds them. Before poo-poo ing my recommendations, try it. I am not saying I am correct 100% of the time, but I am certain the people that read my post...Leave a comment:
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Re: Dell E172fpb
Hi Everyone - I too had this problem with my monitor and (thanks for all your help) it was the old 'bad transistor' issue... I'm actually an electronics engineer, so what follows might make a good read for those of you learning.
Hopefully, the insights I had during the repair process should save you all some $$$... Make sure you read right to the end of this post before you take action.
Firstly [U]you don't need to use the exact same transistor[/U] to replace the faulty ones - Here in Australia, I went through the specs of the original...Leave a comment:
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