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Old 05-08-2006, 09:33 AM   #21
willawake
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Default Re: Dell E172fpb

anybody know the reason for this common failure?
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Old 05-09-2006, 09:26 AM   #22
jumba
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Default Re: Dell E172fpb

Hi All
It is very strange that all faults are the same. Has anyone found the first tube tranistors gone?

I 've looked at the trannies with a multimeter. The one closest back light plug is shorted every which way about 0.01 ohm. The other one is not as drastically damaged but still stuffed. The base emitter resistance is approx 70 ohm with the base to collector still showing a diode characteristic. This type of failure happens when the base is overdriven fusing the base to emitter. The transistor that is shorted between all pins is probably the device has been cooked due voltage punch thru' or by simple thermal runnaway condition. I just find it very odd from the posts that its the second tube transistors that die like mine have. There should be a 50-50 chance of either pair blowing up! Locally, replacements are unavailable and had to resort to importing them. Of the the sucessfull repairs the units that switch off after 2 hrs, have the transistors been replaced with poor equivalent substitutes?

Last edited by jumba; 05-09-2006 at 09:28 AM..
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Old 05-10-2006, 04:49 AM   #23
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Default Re: Dell E172fpb

I have been following with interest this thread as I attempt to sucessfully repair my Dell E172FPb monitor. I found the transistor at Q739 was faulty... I ordered identical replacements from www.bluestar-online.com at $3.89 ea plus shipping to the UK ($24.25 total for 4). The screen ran for three days and then failed on the same transistor, (second replacement failed after a couple of hours). Further research found Norris Parts based in Texas USA at www.repairmylcd.com. They offer replacement boards at $59.95 with payment through paypal... not sure about shipping charges... I had an email exchange with them and they advised the following... "These transistors fail on a lot of these boards. We usually replace the set including Q740. If these fail after replacement then usually the transformers at t754 or t752 are bad. Since these transistors drive these units. We do also replace capacitors and find that the 470uf (c703, c712, c751) seem to fail more than any other."
Hope this info assists....
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Old 05-10-2006, 05:07 AM   #24
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Default Re: Dell E172fpb

Have checked the shipping charge for replacement boards and the cheapest adds another $66 bringing the total charge to some 70 gbp.
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Old 05-10-2006, 05:08 AM   #25
willawake
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Default Re: Dell E172fpb

many thanks. norris parts must be one of the good guys since they gave you so much repair info.
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Old 05-15-2006, 05:02 PM   #26
0zn3r0l
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Default Re: Dell E172fpb

Hi, I recently have replaced the transistors at Q759, Q760, Q740 and Q739 and still no luck.
I have decided to order the replacement DS-1107A Inverter and Power from
http://www.repairmylcd.com/e172-e173...ter-power.html but before I noticed that my board have only 2 connectors for the CCFL lamps, the picture they show on the replacement has 4 and the size of the connectors are smaller. I haven't ordered the board yet and it seems to be the only place to do so.

Has any of you had bought this DS-1107A Inverter and Power from them?
Any advice on this will be appreciated.
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Old 05-19-2006, 12:45 AM   #27
jumba
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Default Re: Dell E172fpb

Got the tranistors yesterday put them and hey presto the unit works again. Time will tell if it is just the tranistors. Purchased 2SD1804 as alternatives from B&D Enterprises.
Min Order $15 which translated to a qty of 32; however shipping more than doubled this figure using UPS global Express (air mail) for a very light item
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Old 05-21-2006, 12:54 AM   #28
enkay78
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Default Re: Dell E172fpb

Hi,
Does some one know what the Blue Cap values are if there is a need to replace some. C771 looks like it cooked and the meter showed that as a short. Moreover transistors Q750 and Q749 are cooked also.
Will changing the Interver board itself be the the best solution since work arounds dont seem to be that effective
regards
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Old 05-24-2006, 11:01 AM   #29
TheBigWhiteWolf
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Default Re: Dell E172fpb

Alright...could someone help a n00b out? How do I get into the case without a dremmel tool? >

I've tried a flat head screwdriver and I've managed to get the bottom edge loose, but the rest of the monitor now looks like a rat's tried gnawing at it...and it's not coming loose.

TIA
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Old 05-24-2006, 01:21 PM   #30
willawake
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Default Re: Dell E172fpb

i have not seen that model. do the usual : check for more screws, remove the stand. think about it, brute force : you will regret later.
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Old 05-31-2006, 06:34 AM   #31
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Default Re: Dell E172fpb

Quote:
Originally Posted by TheBigWhiteWolf
Alright...could someone help a n00b out? How do I get into the case without a dremmel tool? >

I've tried a flat head screwdriver and I've managed to get the bottom edge loose, but the rest of the monitor now looks like a rat's tried gnawing at it...and it's not coming loose.

TIA
Remove the stand by unscrewing 4 crosshead screws loosen the two case halves at the bottom first with a flat head screwdriver twisted in the small gaps and work around the gap unclipping from bottom to top preferably with a soft tool, a wooden ice cream stick works quite well

My nephew has this model with exactly same symtoms shuts down immediately after power up. The board shows discolouration underneath this area : Transistors Q759 Q760 are shorted i am ordering 4 2SD1804 and 4 * 470uf electrolytics to try To replace Q739 Q740 Q759 Q760 C701 C702 C707 C709
will post results
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Old 06-09-2006, 08:06 AM   #32
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Default Re: Dell E172fpb

Hi Folks

Yes, just another fellow with a dead power board. I too have spent a few hours going over and yes mine suffered a blow out at Q759 which damage its mate at 760, I've pulled all the caps off, blue and cans to find all the blue on spec but those 703 and 712 are sus also, as for the rest the board seems fine so its worth a look on the large cans as well. Hope this helps.

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Old 06-10-2006, 02:04 AM   #33
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Default Re: Dell E172fpb

Just to update, I just put in a set of 4 tip41C's as a test of a recommendation, they just fit in and after looking at the specs, if a member on the other site at page 1 can use 2sd1438's (which are very light duty) then a 41C shoud survive.

Well the backlights again fire up but the heat!!!! Phew, ouch, dropped some temporary sinks on and ran for about 15min, but the sinks were only little and thermal runaway is very noticeable.

Give these are cheap and easy trannies to just test with I could care if I destroyed a set. With a multi, I meter the diodes at 751 and 761. I found that 10.9V was present but add .1V for the northern 761. After 15min, therman run away begins and you will see the volts that I let go up to 11.9. with the southern partner following all the way.

A quick makeshift fan and you quickly see the drop back to 10.7 and steady.

Okay, now it might be me but the .1 volt could be a sign of damage to the norther transformers and if you look at the pics re heat affected areas, these transformers cop all the heat when in use.

At 14.7V the unit shuts down but I didn't want to go this high to find out and this was with the buggered transistors in.

Okay as for heat, I could be criticised for using an elcheapo replacement but remember, the heat that can do damage to this board from the original components tells me that it is certainly a poor design.

Since this if for my son, yep, the trannies come out and mounted extenally on a decent sink. That way I will not reck the rest. If this fails, the bin is the next option. I hope this helps.

Mousie
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Old 06-11-2006, 12:15 AM   #34
mousie
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Default Re: Dell E172fpb

Just suffered the same symptoms again like the rest of us, however, now fixed. I just resoldered the board!

It is not the design so much as manufacture as all the component legs appear to have not been cleaned and a quick test with an iron will tell you this with the original solder wanting to part with the legs and I found this accross the whole board. Copper tracks on PCB are not a problem but about 80% of the component legs are dirty and even with high silver content solder pouring in I had some difficulty getting a wet joint and this is the major problem that needs dealing with first. Anyway for any others having this problem, its in the dirty joints and Benq needs a kick for allowing this to happen.

Voltage on the 761 diode is spot on 10v whereas before was at 10.9 or so.

as for the 4 trannies, well they are externally mounted on the rear now so I can keep the heat out of the board.

Hope this solves a lot of heartache.

Mouse
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Old 06-11-2006, 04:18 AM   #35
willawake
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Default Re: Dell E172fpb

good news
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Old 06-24-2006, 02:46 AM   #36
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Default Re: Dell E172fpb

Hi, Just another person that has experienced a failing Dell screen. Like every body else the the screen would show a picture for about 1 sec and then go off and the green light would flash with a clicking sound.

After replacing the trannies ( with 4 tip41C's like mousie) the screen now goes on for about 2 sec and then goes off but the power light stays on and the transitors get really hot (I know they are cheap alternatives).

I am not an electronic guru but know a bit.
Any body got ideas on what may now be the problem?
Have not replaced or tested the capicators yet. Suspect this may now be the cause.
Which capicators should i check and how do I check them using a simple multimeter (got digital and analog)?
Can you check them while they are mounted on the board?

Any help would be great.
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Old 06-24-2006, 05:45 AM   #37
andrew101
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Default Re: Dell E172fpb

whack the monitor on the sides just before the monitor's led turns green
always works for me
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Old 06-25-2006, 10:09 AM   #38
ProtoTech
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Default Re: Dell E172fpb

My E172FPB (by Benq) comes on fine for 2 seconds, then the display goes off, but the green power light stays on.

I found T752 (output transformer on inverter) burned.

So where could I get one?

I assume Dell will be no use, but maybe Benq?

Can anyone post specific contact info to get parts?

Norris Parts in TX is getting them somewhere, since they are rebuilding these inverters and selling the boards on eBay.
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Old 06-26-2006, 04:37 AM   #39
jumba
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Default Re: Dell E172fpb

Repaired display a few weeks a go transistors blew again but noticed that back light was nolonger pure white before tranistors turned up thier toes! I plan to draw cct to figure out the problem. The clue is that the pcb is discloured suggesting the cct is running Too Hot! Two possibilities come to mind either the series cap to the backlight is faulty or the tranny has a shorted turn. This will cause the transistors to run hotter and in the end fail again!
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Old 07-01-2006, 11:53 AM   #40
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Default Re: Dell E172fpb

Hey Prototech,

If you find out the Transformer info let me know. I'm looking to order the same ones. I'm going to go ahead and order all the transistors and capacitors that commonly fail, but don't want to install them until I get the Transformers.

Thanks!!
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