Graham,

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

Thanks for all your help.

--
David Farber
David Farber's Service Center
L.A., CA
wrote in message
...
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" wrote in message
...
So are you saying that it works fine if you replace all four of the
transistors with the BD911's?

--
David Farber
David Farber's Service Center
L.A., CA

wrote in message
...
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


wrote in message
...
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


"David Farber" wrote in message
...
"David Farber" wrote in message
...
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.
--
David Farber
David Farber's Service Center
L.A., CA





wrote in message
...
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.
--
David Farber
David Farber's Service Center
L.A., CA