Mike Easter wrote:

VanguardLH wrote:
If it still has its original battery, that's too old for the battery.

I 'preserved' its battery.

Almost its entire life it was 'sessile'. I read somewhere that the best
way to prolong a battery's life was to 'adjust' its charge to about 35%,
then remove the battery and run on the mains. Occasionally, or if
traveling, I would charge it up to 100%, but then I would take it back
down to 35% and remove it again.

The battery seems to be healthy; and this situation doesn't act at all
like a battery problem. Before it got sick, it ran fine on the mains
alone. This dying business was discovered w/ the battery out. During
external troubleshooting, by 'fiddling' w/ the power situation and
leaving the power connected, I was able to charge the battery from amber
indicator to green indicator.

I also read a little article about how things on the D620 might act up
unpredictably w/ a dead CMOS battery, but I really don't think that is
the situation here, altho' I may look into how much trouble it is to
replace that. I have one around here.

So, the laptop used to work okay on A/C only (no main battery inside)
but now is flaky that way? You said you get a blackscreen. That could
be the lack of power, but it could also be the backlamp(s) burned out in
the monitor. Usually you can put a very bright flashlight against the
screen or pointed at it while nearby to see if you can see a very faint
image on the screen. That means the LCD panel is still working but the
backlamps are off. LCDs work by twisting to determine through which
pixels the light from the diffuser panel (spreads the light sideways
from the backlamps) get passed through the LCD panel. Although the
backlamps are usually replaceable, it requires dismantling the screen
panel, some soldering, and perhaps some butyl tape. Some suppliers sell
a kit with the backlamps, solder, and butyl.

However, as the backlamps go bad, more current is needed from the
inverter used to power them. That means the inverter might be bad, too.
Besides the backlamps, you may have to replace the inverter. With it
all apart, you don't want to do it all over because you replaced just
the backlamps but not the inverter. Yet those together can be pricey.
For a standalone (desktop) monitor, it would've cost me $80 to $120 to
replace the backlamps (2) and the inverter PCB depending if I got the
kit or not and if I got brighter backlamps. I decided to buy a new
monitor instead instead of trying to repair the old one and perhaps
failing in that attempt. Alas, your screen is integral to the laptop.
Sometimes you can find old units for sale but for parts. It doesn't
work but maybe the screen does. I've not tried dismantling the hinge
for the screen to the base of a laptop.

There are Youtube videos on how to replace backlamps in a laptop. There
look to be some for your model or similar. Just remember that the parts
you buy (backlamps, inverter board, butyl seals, etc) is a lost expense
if you fail in the repair. For that old a laptop, especially since you
already have a Chromebook, I wouldn't waste the money or time repairing
the screen.

The coin cell battery in laptops is usually a royal pain to replace.
Often the shell has to be dismantled: take the two halves apart, the
keyboard off, and the CMOS battery is on the top-side of the mobo
instead of on the bottom (which rarely has an access cover if on the
bottom of the mobo, anyway).

The CMOS battery keeps alive the /copy/ of the BIOS settings from the
EEPROMs into the RTC chip (where is the CMOS memory). Those are the
BIOS settings you use on power up. The EEPROM copy gets read only when
you reset the BIOS back to factory defaults. If the CMOS battery is
weak or dead, it can cause corruption in the CMOS copy of the setting or
they are lost (in which case the EEPROM copy should get copied back into
the CMOS copy). Make sure to put in a fresh CR2032 (likely type) whose
shelf life is a few years away.

https://www.youtube.com/watch?v=KH4UyR27ocA

The author says just the keyboard needs to be removed to get at the CMOS
battery. That's easier than having to disassemble the shell to get at
the mobo. Alas, the coin cell battery doesn't just slide into a holder.
That would be easy. You have to get a coin cell battery that has the
leads and connector attached. That'll raise the price and lower the
availability. You could unsolder the wires from the old battery to
solder onto the new battery; however, you need to use silver solder and
silver solder flux with the stainless steel case for the battery. That
requires more heat, so you'll likely damage the battery. You don't have
the equipment to do a quick electric or tack weld. If you're lucky,
maybe they designed the holder with the attached leads to let you pop
out an in the coin cell battery.