🐙
Doing something a little different today: starting on restoring my ThinkPad 701C. This is the model with the famous “butterfly” keyboard. I lucked out and bought it from someone who cleared out some rich person’s home up in Vail. First off is that there is no display backlight. Fortunately I have the port replicator so I can connect an external monitor.
Also there’s bad RAM. The BIOS helpfully detects it and reduces the available memory, but Windows 95 won’t start with that little RAM.
Welp, it’s time to open this up. Fortunately there are step by step guides on how to do so. I’d hate to damage the keyboard unfolding mechanism!
First big step is getting the top plate off which reveals a manufacture date of Feb 13 1995. A made a small mistake and cracked some of the brittle plastic around one of the tabs that old down the top plate. I’ll need to be more careful!
While I have this off and it’s still mostly assembled I’ll test the voltage going to the backlight. It’s 1.928VAC at 120Hz. That voltage seems low, but I know nothing of CCFL backlights. Maybe it’s fine?
@polpo You sure you aren't measuring the (pulsed) DC side? Because that's at least one or two orders of magnitude too low for CCFL
@baldengineer I'm not sure... the only two wires that go to the display that aren't on the delicate flex cable are these two. I'm kind of out of my depth here!
@polpo I am not super familiar with how the converters work. But I know CCFLs take 10s to 100s of volts to work.
So if you're only seeing ~1 volt AC, either the switching frequency is much higher than your DMM can read, it isn't the hot side, or I'm misunderstanding how the backlight works.
Good chance it's the last one.
I mean, I was basically telling him to recap it without telling him to recap it 😛
@48kRAM @baldengineer Hopefully all it takes is a recap!! The inverter boards for the 701C have all kinds of other stuff on them and are impossible to find.
@baldengineer @polpo I was gonna guess the HV PSU is effed and, therefore, getting current-starved and putting out way too few volts. But... just a hunch based on all the folks I've been watching rehab ThinkPads lately.