Screen (LCD panel) compatibility? D820

Yes, even a seemingly minor difference in the part number can mean the panel won't work.

What was wrong with the original panel?  It's possible the inverter is the problem -- in which case you won't see anything on the screen other than in very bright light.

Does this system have an nVidia-based mainboard?  If so, this line of chips is well known for faulty nVidia engineering -- and they can fail in such a way as that an external screen will work when the internal one doesn't (i.e., exactly as you'd expect when it's the screen that's bad, not the video chip/mainboard).

Yes, even a seemingly minor difference in the part number can mean the panel won't work.

Thank you.  Sadly that looks like the answer then.

What was wrong with the original panel?  It's possible the inverter is the problem -- in which case you won't see anything on the screen other than in very bright light.

Please see the photo that I posted at the beginning of this conversation.  This is a photo rather than a screenshot, because the BIOS was beginning to boot the PC -- and besides, if I waited for Windows to boot and then captured a screenshot, the screenshot would show the intended contents and would not know about the screen's defect.  An external monitor works correctly.  Also if the inverter were the problem, there wouldn't be a white band running down the middle of the screen.

Does this system have an nVidia-based mainboard?

Yes, but that doesn't explain why the minor difference in part number causes the other screen to display nothing at all when Dell's screen still displays most of the contents correctly.

If so, this line of chips is well known for faulty nVidia engineering -- and they can fail in such a way as that an external screen will work when the internal one doesn't (i.e., exactly as you'd expect when it's the screen that's bad, not the video chip/mainboard).

Thank you.  No one provided this information when I asked questions previously.  So there's still a chance that the primary problem is in nVidia instead of Dell's screen, independent of the secondary problem that HP's screen didn't display anything.

Now for a tangent on nVidia's defect, I gave an Inspiron 1720 to relatives.  The Inspiron 1720 is mysteriously missing from Dell's list of affected models.  The one that I gave to relatives developed the same problem that nVidia is famous for, completely garbling the contents of the screen.  I asked them to boot it once a week to keep the electronics in shape until I can try replacing the video board.  So they did.  And then suddenly a week ago that 1720 started working.  So nVidia's problem is intermittent, and the 1720 video board that I bought on eBay might remain unused.  My other 1720 has been working fine.

Did you let Windows load?  A display that cannot be ID'd (the BIOS reads the EDID of the panel) won't show an  image, but should once Windows loads.

Though it looks like a bad panel, the presence of a GeForce chip of this era makes that a prime suspect.

As for the Inspiron 1720, nVidia never came truly clean on exactly what it did to address the problem (other than recommending BIOS updates that ran the fan faster and longer to keep the temperatures down).  Most I've seen who analyzed the problems say that ALL the 8400GS and 8600GT mobile chips are bad, and that they were never re-engineered to solve the problem.  Yes, the problems are intermittent at first, but once the chips go bad, the slide to oblivion is inevitable - they eventually fail completely.  Doesn't matter if it's a Dell, HP, Apple, Lenovo -- they all eventually fail.

Did you let Windows load?  A display that cannot be ID'd (the BIOS reads the EDID of the panel) won't show an  image, but should once Windows loads.

Thank you!  I'll try it in a few days when I have time to experiment again.

Though it looks like a bad panel, the presence of a GeForce chip of this era makes that a prime suspect.

Right, if HP's screen displays mostly valid stuff with a vertical white stripe after Windows loads, we'll know it's the chip.

Most I've seen who analyzed the problems say that ALL the 8400GS and 8600GT mobile chips are bad

That's my understanding too.  That makes me think Dell hasn't come clean either, omitting the Inspiron 1720 from the list of affected models.  I was amazed to learn that my relatives' 1720 started working again.  But if it's going to fail again, I guess the replacement card from an eBay auction will be useful after all, for a few more years.

Did you let Windows load?  A display that cannot be ID'd (the BIOS reads the EDID of the panel) won't show an  image, but should once Windows loads.

After Windows loads, HP's screen is still black.

The power button put the PC in sleep mode, I switched the screen back to Dell's screen, and awakened the PC.  Then Dell's screen was black.  I held the power button to power off the PC, then rebooted, and this time Dell's screen came alive, displaying valid contents outside if its white vertical band.

So it looks like the BIOS detects that it dislikes HP's screen because of the different trailing (submodel)(numbers), and then Windows takes information from the BIOS.

I paid the equivalent of US$40 for HP's screen.  It was a learning experience.  It's not worth spending more money on either this Dell PC or HP screen.  I wonder if a junk dealer will appreciate a working DVD drive, 2GB DDR2 RAM board, battery, and keyboard, or should I keep the working parts.

If you get nothing on the screen once Windows loads, it's the video chip that's bad.  The EDID mismatch will prevent a BIOS screen from showing up but you should still see an image once Windows loads.

But when I switched back to Dell's screen, before a reboot Dell's screen was also black but after a reboot Dell's screen returned to its situation shown in the photo, mostly valid but with a white vertical band.  If the video chip were the cause of a 100% black screen, Dell's screen would suffer the same as HP's screen.

Well, too bad I wasted money on HP's screen.  I couldn't get a Dell WUXGA screen for a worthwhile price which is why I bought an HP WUXGA screen.

I bought a Dell WXGA screen for a reasonable price, though it's sad to lose half the resolution.  It's working.