3400c Display Conundrum

[Njb796]

Hi all… new here but spent some extensive time on this forum reading advice and tips from trusted folks like all of you as I rehab two 3400s. I searched far and wide to find a solve for this. Thoughts from experts? It’s not the backlight. Also, when I say “display” below I mean the built in LCD and case.

Two Powerbook 3400s. We’ll call them A and B.
A has a bright crisp display. B has a display, but much dimmer… think pre-sleep dim.

I switch the displays (unmount the whole top display and reattach to the other) and get the same result (meaning the issue stays with the computer, not the display) so I don’t think its the display because the issue doesnt follow the display. So after the switch, B is still dim even though it has A’s bright display.

What else I have done:
Reseated connections everywhere.
Replaced PRAM batt (no previous leak detected).
Swapped power boards.
Did a PMU reset with back button 30sec no power.
Reset parameter RAM 5 chimes/times

Any other thoughts? Could it be a capacitor recapping needed somewhere on the logic board? Could it be the RAM? Could it be haunted? (I know… grasping at anything here)

FWIW, machine A has 80mb of RAM and is 200mhz, and machine B has 144 RAM and is 240mhz and machine B takes 45 seconds longer to boot (identical system folders).

 

[Njb796]

Adding: Both always on A/C power. One Li-Ion batt was working perfect then while left for two weeks in sleep mode, completely drained the batt to nonexistence now and wont recharge. It happened in a blink… well… 2 week blink. Long story short, both are on AC power (but welcome any tricks for the batt… i cant even get a light up test on the built in tester on the side)

 

[Njb796]

PPS: I have to add: Yes I tried the brightness buttons. Both set to max.

 

[Durosity]

AThis isn’t a system I’ve had particularly large amounts of time spent on, but my immediate suspicion will be an under/over voltage issue to the inverter. Maybe you could use a multimeter to map out both sets of pins on the display connector and see if there’s any variation between the working logic board and the system containing what we suspect is the faulty one to confirm?

 

[Njb796]

I could certainly do that. Assuming its that, whats the solve then? Is there one?

 

[Durosity]

That's the question.. assuming it's that then we'd need to work out what components control that and attempt to test them. But there's no point doing anything like that until you've been able to confirm any differences on the output from those connectors.