Dell E177FPc - no brightness adjustment

[tmcw]

I have 2 of these monitors with exactly the same problem in that the brightness doesn't change when attempting to change the brightness.

Contrast does work, and everything else seems to be ok. Not sure at what level the brightness is actually at, but it's at a fairly good level for normal working, just want to try and get it to change brightness when change is attempted.

I opened up the monitor, and the caps look ok, in fact, most of them are either Rubicon YXG or Nichicon KY.

I've included a link to the service manual. I'm not an electronics tech, but hoping someone might be able to point me in the right direction where to start. The manual is fairly detailed with drawings, schematics, etc.

linfotech.co.uk/schematics/dell/Dell_e177fpc.pdf

[selldoor]

Re: Dell E177FPc - no brightness adjustment

Could be a problem on the main board - does the voltage on the Dim line change when
you try to adjust.

[tmcw]

Re: Dell E177FPc - no brightness adjustment

Thanks for the reply.

With a bit of contortion, I managed to test the DIM line, and as far as I can tell, it's ok.

Pin 2 on the connector from the main-board to the power-board was showing the following:

@ 100 brightness, 5.05V
@ 50 brightness, 2.001V
@ 0 brightness, 30mV

Not exactly linear, but I'm guessing this would be fairly typical?

So I should now be looking somewhere on the power-board?

[stj]

Re: Dell E177FPc - no brightness adjustment

R210
R213
R214
c210
those are the only parts related to dimming other than the chip. ic201
all on page34

[selldoor]

Re: Dell E177FPc - no brightness adjustment

Seems odd that 2 monitors are doing the same?

Are you testing separately - not on a dual monitor system?

Are they recognised fully by the PC

Check the brightness is not software controlled Win 7 and 8 had some
weird self setting thing.

try a full settings reset?

When you change the setting does the bar move on the osd?

http://stuartconnections.com/product...etup.htm#Using the Front Panel Buttons

[stj]

Re: Dell E177FPc - no brightness adjustment

i would hope the testing is taking place WITHOUT a pc connected.
using just the on-screen menu's and preferably starting with a factory-reset.

[tmcw]

Re: Dell E177FPc - no brightness adjustment

I didn't check both monitors for the voltage on the DIM line, just one of them, but through the brightness/contrast menu, they seem to behave similarly, and I was testing them separately (not on dual monitor setup).

Both fully recognised by the PC, I've one currently connected to the VGA out of a media player, but it's the same issue with that connected.

I don't think these monitors had any control from the PC software, not that I'm aware of anyway. There is nothing in the OSD menus to suggest it's possible.

Have just tried a factory reset, but the issue remains.

Yes, the bar does move as expected back and forth between 0 and 100 when the front panel buttons are pressed.

R210, R213, R214, and C210 are all those small components on the solder-side of the power-board.

And while I think of it, I have a bunch (4 or 5) older Dell monitors (E173FP variants) that all also have the same brightness issues. They all had 2 seconds to black issues which were restored by changing the usual suspect caps on the power-board, but the no brightness control then appeared on them.

I haven't changed any capacitors or other components on these 2 E177FPc monitors yet.

Have there been reports of the older monitors with brightness control issues?

[tmcw]

Re: Dell E177FPc - no brightness adjustment

i would hope the testing is taking place WITHOUT a pc connected.
using just the on-screen menu's and preferably starting with a factory-reset.

If there is nothing connected to the VGA, and the monitor is powered up, it goes straight to a "self test feature check" box with coloured strips that move about the screen like a screen-saver.

Is there another way to get into the OSD menus? I couldn't see anything from the service manual.

Also, just to say that the brightness adjustment does give a very slight change when going from 0 to 100, but it's really only noticeable on the black colours, and I only noticed it because it's getting dark outside here. The change is barely perceptible on brighter and white portions of the screen.

[budm]

Re: Dell E177FPc - no brightness adjustment

Look at the screen in the darkened room with the power switch is OFF, do you see the screen glowing at all?

[tmcw]

Re: Dell E177FPc - no brightness adjustment

Do you mean with no power applied whatsoever, or with the monitor plugged in, but switched off via the panel button at the front of the monitor?

I thought maybe I was going a bit mad, so I pulled out a newer Acer and a Samsung monitor, and adjusting the brightness on those two does give a very noticeable change in the brightness from full to zero.

But on the Dells, brightness change, if any, is barely noticeable. Maybe they've always been like that, I haven't had them from new. There are a number of Dells at work, I'll have a look at a few tomorrow and see if they're similar, or have a good degree of difference between fully up and fully down.

[stj]

Re: Dell E177FPc - no brightness adjustment

you wont have such a wide range if the tubes are old - but it's still going to be noticeable.

[tmcw]

Re: Dell E177FPc - no brightness adjustment

To confuse me further, I found this document that seems to imply that "brightness" is contrast, and "contrast" is brightness. However, the explanation there is for CRTs, so it seems that I'm seeing something on these LCDs that is similar to what would be observed on a CRT.

http://www.poynton.com/notes/brightness_and_contrast/

I've had a look at a few LCD monitors since, and what I would expect from brightness range, isn't quite what I'd expect.

When I adjust contrast, the screen goes from bright to very dark. (I would have expected the lamps to go from their brightest to darkest when adjusting the "brightness" function).

Maybe different branded LCD monitors have very different ranges in the "brightness" or BLACK LEVEL that they can achieve, and the Dells that I've looked at have a particularly narrow range.