Anyone seen this behavior after replacing lcd panel?

[merkin]

I have replaced many cracked lcd panels in laptops, and had 100% success until now.

The culprit is a dell inspiron 1420.

Bought a cheap, but compatible lcd panel from ebay.

Everything works fine, except the panel seems less bright than the original.

MORE IMPORTANTLY when I adjust the screen brightness with the function key on the keyboard(fn+arrow up/down) the highest setting is less bright than the second and third highest settings, which doesn't make any sense.

The original inverter is still being used, which leads me to believe the ccfl in the replacement panel may be the issue.

Any comments, suggestions, questions?

Thanks in advance.

[thesloc]

Re: Anyone seen this behavior after replacing lcd panel?

It's the CCFL lamp on the LCD, since you bought an used one you most likely bought an old one.

[merkin]

Re: Anyone seen this behavior after replacing lcd panel?

Hi,
But that does not explain why the highest(brightest) setting is dimmer than the second and third to the highest setting.

ALSO I just noticed that every time I shutdown or restart the laptop, it does not retain the brightest setting which was set prior to restart/shutdown.

Does this issue make sense as I explained it? If not I will try to explain it better and be more detailed.

Thanks again.

[b700029]

Re: Anyone seen this behavior after replacing lcd panel?

Here's a schematic:
http://lqv77.com/download/294/
(That's right, it's an Asus )

LCD connector top left of page 28... brightness and contrast is controlled via SMbus. No schematic available for the inverter side of things but I'm guessing there's an IC there which is addressable via SMbus and controls the inverter. That's the part from the new panel that's behaving oddly, it might be a factory reject or just defective. Brightness settings not persisting also can be explained by that, it's either an IC with integrated nonvolatile flash or an external EEPROM. Post some pictures of the panel connections and any PCBs it has if you want to figure this out.

[merkin]

Re: Anyone seen this behavior after replacing lcd panel?

Thanks for the schematic.

I found someone with identical issue
http://en.community.dell.com/support.../19313203.aspx (read his brightness steps)

Looks like issue is that the panel is not an EXACT replacement. Funny that only happens with a DELL. Oh well, thanks again guys.

[b700029]

Re: Anyone seen this behavior after replacing lcd panel?

That description of what happened to the different brightness levels is really reminiscent of data bits being shuffled around. E.g. with 8 levels there should be 3 bits of brightness, like this:

000 0
001 1
010 2
011 3
100 4
101 5
110 6
111 7

Switch around the bits, e.g. the first and the last, and you end up with a weird counting order that can explain why the brightness goes both up and down:

000 0
100 4
010 2
110 6
001 1
101 5
011 3
111 7

That description of "half as bright" also suggests maybe his replacement LCD wants 4 bits instead of 3, so he can only use 8 out of the 16 levels.

[artois7]

Re: Anyone seen this behavior after replacing lcd panel?

Yeah I've had this problem on both a Dell and a Toshiba, I figured they were just slightly incompatible panels, but as cheap laptops they were fine.

[merkin]

Re: Anyone seen this behavior after replacing lcd panel?

@b700029,
Thanks again for the great explanation.

What is your guess regarding why the brightness level gets "reset" every time the laptop gets restarted or shutdown?

[b700029]

Re: Anyone seen this behavior after replacing lcd panel?

Brightness settings not persisting also can be explained by that, it's either an IC with integrated nonvolatile flash or an external EEPROM.

.

[merkin]

Re: Anyone seen this behavior after replacing lcd panel?

Replaced with exact OEM replacement and problem is resolved. Thanks again to everyone who responded