Red tint on Dell 19" M992 Monitor

C

Jan 1, 1970
0
I bought this monitor recetly at a boxing day sale at a great price ($10). I fired it up and noticed a slight red tint immediatley. Blue and green seem to work fine. The on screen controls won't let me get into the rgb adjustements (cant find any info on service mode either), and the computer's video card is too crummy to allow me to adjust the RGB levels there. The previous monitor that was connected to it, a 15" daewoo, had no color balance problems. I opened up the monitor and removed all the shielding. The only pots present are labeled YH YV YV-s and YH-c (or something like that) and they appear to be related to the deflection circuits so i left them as is. The VGA cable goes directly to the board at the back of the yoke, I searched for bad solder joints, resolderd anything that looked suspicious and it made no difference. This monitor is 3 years old, it seems a little early for it to be worn out. This problem doesnt change as the monitor warms up. I can live with it but does anyone have an idea of what i should do?? D Dave D Jan 1, 1970 0 Captain Napalm said: I bought this monitor recetly at a boxing day sale at a great price ($10).
I fired it up and noticed a slight red tint immediatley. Blue and green
seem to work fine. The on screen controls won't let me get into the rgb
adjustements (cant find any info on service mode either), and the
computer's video card is too crummy to allow me to adjust the RGB levels
there. The previous monitor that was connected to it, a 15" daewoo, had no
color balance problems.

I opened up the monitor and removed all the shielding. The only pots
present are labeled YH YV YV-s and YH-c (or something like that) and they
appear to be related to the deflection circuits so i left them as is.

A very wise decision!
The VGA cable goes directly to the board at the back of the yoke, I
searched for bad solder joints, resolderd anything that looked suspicious
and it made no difference. This monitor is 3 years old, it seems a little
early for it to be worn out.

This problem doesnt change as the monitor warms up. I can live with it but
does anyone have an idea of what i should do??

Modern monitors tend to use digital alignment software to adjust settings,
internal 'pots' have been superceded where possible. There's only two ways I
know of that you can adjust engineering settings these days on this type of
monitor.

The first one is obvious, obtain the correct software and interface and use
your PC to align the monitor. This is extremely expensive and not practical
for a one-off!

The second one is a bit of a hack. In very basic terms, to control
engineering settings, your monitor uses a micro and a digital to analogue
converter. The output from the d-a converter is an analogue voltage level
between 0V and 5V. This is used to control the circuit in question. In your
case we are interested in the red level. Somewhere on the crt base PCB there
will be a way of controlling the red background/drive level and this control
voltage will be present.

What you need to do ideally is to find this d-a output which controls the
red level and cut the pcb track. This will mean the D-A converter now has no
control over the circuit in question. Fit a small pot with the wiper going
to the the track which leads to video circuits, left leg going to ground and
the right to the regulated 5V line. Adjusting this pot will theoretically
give you full manual control over the circuit in question.

The problem is that without a schematic and a bit of experience you will
have to be very determined to find the correct control line- there are many!
It might be as simple as looking up the datasheet of the video IC on the crt
base and seeing if it has control inputs for RGB levels.

If you don't have any experience with monitor or TV repair then I strongly
advise you not to attempt this yourself. It's easy to make a mistake when
making modifications of this nature, and it's possible to destroy the
monitor or yourself in the process!

The red tint could be down to an ageing crt or a failed\out of tolerance
component. Making adjustments for an ageing crt is fine and perfectly
acceptable, but doing so for faults is not. The root cause of the problem
must be diagnosed before making adjustments.

Dave

C

Captain Napalm

Jan 1, 1970
0
Dave D said:
That hack sounds interesting. I am wondering though, can I not put the put
inline with the red output that comes in through the SVGA cable? With
componsite, a lower voltage will present will a darker picture, and since
the red output is labeled on the board and easy to get to, perhaps I can
just desolder the SVGA red before it gets to the board and place a pot
there?

The second one is a bit of a hack. In very basic terms, to control
engineering settings, your monitor uses a micro and a digital to analogue
converter. The output from the d-a converter is an analogue voltage level
between 0V and 5V. This is used to control the circuit in question. In
your case we are interested in the red level. Somewhere on the crt base
PCB there will be a way of controlling the red background/drive level and
this control voltage will be present.

What you need to do ideally is to find this d-a output which controls the
red level and cut the pcb track. This will mean the D-A converter now has
no control over the circuit in question. Fit a small pot with the wiper
going to the the track which leads to video circuits, left leg going to
ground and the right to the regulated 5V line. Adjusting this pot will
theoretically give you full manual control over the circuit in question.

The problem is that without a schematic and a bit of experience you will
have to be very determined to find the correct control line- there are
many! It might be as simple as looking up the datasheet of the video IC on
the crt base and seeing if it has control inputs for RGB levels.

If you don't have any experience with monitor or TV repair then I strongly
advise you not to attempt this yourself. It's easy to make a mistake when
making modifications of this nature, and it's possible to destroy the
monitor or yourself in the process!
Not a big problem for me, I have a lot of training in electronics including
TV repair as it may be required by my employer.

The red tint could be down to an ageing crt or a failed\out of tolerance
component. Making adjustments for an ageing crt is fine and perfectly
acceptable, but doing so for faults is not. The root cause of the problem
must be diagnosed before making adjustments.

True, I will test various resisters and diodes next time I am in there. I
read this one message posted by a tech that picture tint in dell monitors is
notoriously caused by a particular IC (i cant remember which one, or if this
monitor has it), but I'm not going to go through the trouble of aquiring a
replacement if i can hack it to work. Its only on a second computer anyways.

D

Dave D

Jan 1, 1970
0
Captain Napalm said:
That hack sounds interesting. I am wondering though, can I not put the put
inline with the red output that comes in through the SVGA cable? With
componsite, a lower voltage will present will a darker picture, and since
the red output is labeled on the board and easy to get to, perhaps I can
just desolder the SVGA red before it gets to the board and place a pot
there?

It might help, but if the picture has an overall red tint then that
indicates the black level has too much red, which won't be helped by
reducing the red input level.

Also, adding a resistor will upset the 75Ohm impedance match between the
video card and the monitor, which may give undesirable results.

Dave

C

Captain Napalm

Jan 1, 1970
0
Your right I never thought of it like that. Upon closer examination, it
looks like even parts of the screen that are illuminated but not actually
drawn by the video card are still tinted red, so my version of the hack wont
be effective. I think I might just have to start at the red gun and trace
back every component that I'm able to test back to the cable. It shouldn't
take long as the board is small and there arent very many components on it.
Failing to find anything wrong, its ICMaster.com to start looking up
pinouts.

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