Dell 17" LCD monitor shuts down.

[David Farber]

This 17" Dell monitor, model number CN-0M1609-4633-3AG-2DTL, will power on
when AC is first applied. In the middle of the screen appears, "Dell Genesis
Display Perfection." Then it disappears after a second. When you press the
power button with no input signal, the Dell self test feature check
illuminates in the bottom left corner of the display. You can see the red,
green, blue, and white bars within the self test box. Then, it starts to
scroll diagonally up to the right for about a second and then the display
turns off. The power light remains on. If you hook it up to a PC, you do not
get any display. The boards are in good condition and I reflowed the solder
over many of the components with no improvement. Any ideas what might be
going on here?

Thanks for your reply.

 

[Simoc]

Bad caps?

 

[David Farber]

Bad caps?

The caps tested ok.

Thanks for your reply.

 

[DaveM]

This 17" Dell monitor, model number CN-0M1609-4633-3AG-2DTL, will power on
when AC is first applied. In the middle of the screen appears, "Dell Genesis
Display Perfection." Then it disappears after a second. When you press the
power button with no input signal, the Dell self test feature check
illuminates in the bottom left corner of the display. You can see the red,
green, blue, and white bars within the self test box. Then, it starts to
scroll diagonally up to the right for about a second and then the display
turns off. The power light remains on. If you hook it up to a PC, you do not
get any display. The boards are in good condition and I reflowed the solder
over many of the components with no improvement. Any ideas what might be
going on here?

Thanks for your reply.

Did you check the power supply voltage(s)? Low power supply voltage and high
ripple/noise can create a myriad of symptoms.

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Some days you're the dog, some days the hydrant.

 

[Jim Yanik]

Why did you reflow solder? Were there bad joints or intermittents?

The caps tested ok.

Thanks for your reply.

tested how? ESR meter? capacitance meter? ohmmeter?

 

[David Farber]

Why did you reflow solder? Were there bad joints or intermittents?


tested how? ESR meter? capacitance meter? ohmmeter?

--
Jim Yanik
jyanik
at
kua.net

ESR with my Bob Parker, ESR meter and an ohmeter for shorts.

Thanks for your reply.

 

[David Farber]

Why did you reflow solder? Were there bad joints or intermittents?


tested how? ESR meter? capacitance meter? ohmmeter?

--
Jim Yanik
jyanik
at
kua.net

ESR with my Bob Parker, ESR meter and an ohmeter for shorts.

Thanks for your reply.

 

[me]

Judging from the described defects in operation there seems to be a problem
in the electronic circuitry. I advise a basic troubleshooting routine be
performed on this device to localize the defective circuitry.

 

[Guest]

Hi David

I bought aDell E172fp off Ebay recently which was sold as faulty, the Power
Light would flash on/off with no display.

Basically, what i have found is that the output transistors go s/c, these
are the small 2sc5707 transistors that sit near the 4 yellow transformers. i
had 2 go s/c in one of the channels, the other channel was ok. I replaced
these and now the green light stays on , the display comes on for about 3
seconds like you's does and then goes off.

I put a scope on the o/p of the transformers and can see them switching ok
for 3 secs then the o/p goes off. What is happening is that the Pulse Width
Modulator chip that drives the lamps is shutting down after 3 seconds, this
is the 16 pin chip marked TL1451A. I have the datasheet on this chip and i
am currently trying to work out why it shuts down. I have found that whe
you first switch on the monitor, the supply to this chip is 18vdc, when the
display comes on for 3 seconds this drops to 14 volts (because this supply
is unregulated) and then goes back to 18vdc.

I would be interested to know if you can confirm the dc voltage you are
seeing on pin 9 the 16 pin TL1451A chip during this startup period and
see if it compares to my results.

Theres a common problem here with these monitors, it may be overcurrent due
to s/c transformers or another transistor s/c somewhere, i am sure we will
track it down shortly.

Graham

 

[David Farber]

Hi David

I bought aDell E172fp off Ebay recently which was sold as faulty, the Power
Light would flash on/off with no display.

Basically, what i have found is that the output transistors go s/c, these
are the small 2sc5707 transistors that sit near the 4 yellow transformers. i
had 2 go s/c in one of the channels, the other channel was ok. I replaced
these and now the green light stays on , the display comes on for about 3
seconds like you's does and then goes off.

I put a scope on the o/p of the transformers and can see them switching ok
for 3 secs then the o/p goes off. What is happening is that the Pulse Width
Modulator chip that drives the lamps is shutting down after 3 seconds, this
is the 16 pin chip marked TL1451A. I have the datasheet on this chip and i
am currently trying to work out why it shuts down. I have found that whe
you first switch on the monitor, the supply to this chip is 18vdc, when the
display comes on for 3 seconds this drops to 14 volts (because this supply
is unregulated) and then goes back to 18vdc.

I would be interested to know if you can confirm the dc voltage you are
seeing on pin 9 the 16 pin TL1451A chip during this startup period and
see if it compares to my results.

Theres a common problem here with these monitors, it may be overcurrent due
to s/c transformers or another transistor s/c somewhere, i am sure we will
track it down shortly.

Graham

Hi Graham,

I checked those 2SC5707 transistors again. This time I found two of them,
Q759 and Q760, were shorted b-e. I'll order those parts, replace them, and
let you know what happens.

Thanks for your reply.

 

[Guest]

David, ok, i havent been able to get any of them over here but i have used
BD911 as test devices.

If you get a minute would be interested to know what voltage you have on
pin9 of the PWM chip as i mentioned in my last post.

Graham

 

[David Farber]

David, ok, i havent been able to get any of them over here but i have used
BD911 as test devices.

If you get a minute would be interested to know what voltage you have on
pin9 of the PWM chip as i mentioned in my last post.

Graham

Graham,

Is it ok that the bad transistors are removed when I check the voltages? I
haven't received the replacements yet.

 

[Guest]

Hi David, i believe it should be ok with the trannies out, it just means
that one channel will not be driven.

Would be interested to know if you still have the same symptom (on for 2-3
secs and then off) with the trannies out.

I think what is happening is that the PWM chip is detecting overcurrent and
shutting down. I found that with BD911 transistors in in place of the
2sc5707 i am still getting the same problem but i cant find any more s/c
devices. As i understand it , with these monitors this is a real common
problem, even if you manage to get the thing working its likely to break
down again, with the same devices s/c a day/week/or even months later. It
seems its always the same channel (the top lamp) that goes but no-one really
knows why. I also understand that the transformers are suspect and go s/c or
arc internally. Dry solder joints are also a major problem as are poor
quality electrolytic caps.

I am coming to the conclusion that this monitor suffers from a major design
fault from new, they seem to just make it out of warranty and then fail

Apparently many service shops now refuse to handle them, they are a warranty
claim waiting to happen.

I am going to continue working on it though as i hate to give up on things
like this, its my own monitor so cost isnt an issue but for repair shops it
well cold be.

Anyway, let me know what you find with the voltages, should be interesting.

Regards

Graham

 

[David Farber]

Hi David, i believe it should be ok with the trannies out, it just means
that one channel will not be driven.

Would be interested to know if you still have the same symptom (on for 2-3
secs and then off) with the trannies out.

I think what is happening is that the PWM chip is detecting overcurrent and
shutting down. I found that with BD911 transistors in in place of the
2sc5707 i am still getting the same problem but i cant find any more s/c
devices. As i understand it , with these monitors this is a real common
problem, even if you manage to get the thing working its likely to break
down again, with the same devices s/c a day/week/or even months later. It
seems its always the same channel (the top lamp) that goes but no-one really
knows why. I also understand that the transformers are suspect and go s/c or
arc internally. Dry solder joints are also a major problem as are poor
quality electrolytic caps.

I am coming to the conclusion that this monitor suffers from a major design
fault from new, they seem to just make it out of warranty and then fail

Apparently many service shops now refuse to handle them, they are a warranty
claim waiting to happen.

I am going to continue working on it though as i hate to give up on things
like this, its my own monitor so cost isnt an issue but for repair shops it
well cold be.

Anyway, let me know what you find with the voltages, should be interesting.

Regards

Graham

Hi Graham,

I checked the voltage at pin 9 of the TL1451A chip and have come up with the
same results that you found in your monitor. The voltage swings from 14 to
18 volts after shutdown.

 

[Guest]

Thanks David, will be interesting to see what happens after you get the
replacement transistors in. Perhaps my continuing problems are due to having
tried BD911 transistors in place of the 2sc5707.

Let me know how you get on please.

Graham

 

[Guest]

Just made another interesting observation on this board.

When the board has 2 BD911's fitted in place of the 2sc5707 in 1of the
channels and has 2sc5707's in the other channel then plugging in a pair of
ccfl tubes gives the same symtoms (works for 3 seconds or so then goes off).
The 2sc5707 transistors have been removed and metered and appear to be ok.

If i put BD911's in both channels then the unit works (stays on). If i
unplug one of the CCFL tubes then i get the original fault and the unit goes
off after 3 secs or so.

I am wondering if the Pulse Width Drive chip that drives the ccfl tubes is
detecting an im-bablance in the 2 channels and is shutting down.either that
or the 2 2sc5707 transistors are still defective despite reading ok on cold
test.

Tricky one this !!

Graham

 

[David Farber]

So are you saying that it works fine if you replace all four of the
transistors with the BD911's?

 

[Guest]

Hi David, sorry if the last post was a but confusing. What i was trying to
say was that the circuitry seems to be very sensitve to an im-balance in any
1 channel.

When i was doing some comparitive resistance checks on the 2 channels the
other day i noticed about 700k difference in resistance around the area of
the 2 transistors, this was traced to having different transistor types in 1
channel. I think the PWM detects this difference in current flow in 1
channel and shuts down.

All i would say is replace all 4 2sc5707 transistors (2 per channel) plug in
the ccfl's and see what happens. If it works , then, as a test unplug 1 of
the ccfl tubes and you will see it shuts down again.

Also, if you replace the trannies and you get the same symptoms try plugging
in a different pair of ccfl's , you might have a duff tube which is causing
the imbalance.

Let me know how you get on

Graham

 

[David Farber]

Graham,

I substituted the four 2SC5707's with the BD911's and now the monitor works
fine.

Thanks for all your help.

 

[McRight2k]

Graham,

I substituted the four 2SC5707's with the BD911's and now the monito
works
fine.

Thanks for all your help.

Hi David & Graham,

i'm spanish, and my english is regular sorry

so...
i have find solutions for my problem at my Dell e172FP in google and
find this post that you recently reppairs it.
My monitor bought at eBay too like Graham but i both new more than
years ago. It was new in his original box and it works fine eve
today.
It turn on and the display show anything during 1 second (or less) an
then display off and the led green flash on/off quickly. I think it
like Graham occours.

Well, i don't undestand well yours and i think the solution is chang
the C5707's transistors (Q759, Q739, Q760, Q740) with 4 BD911??
i see that David works fine, but i don't undestand if Graham too work
already with do it???

I try repair in the shops here, at Spain, and they not want repair it
and Dell say that they sold me any repaired for me less expensive tha
new, but a bit. i don't interest this option, if i can repair it bette
than better.

Thank for your reply.
McRight2