2021 Dec 4

The power adapter and CF-to-IDE adapter arrived about a week ago. The good news
is that the adapter seems to work. It makes a slight whine when turned on and
gets fairly hot, but is otherwise fully functional. The cable was very sticky,
covered in some glue and the usual old rubber feel, but I was able to mostly
clean it with some rubbing alcohol. I also managed to remove the broken plastic
on the back of the ThinkPad without breaking it. I think it can be glued back
together in the future, but for now I just want it out of the way so it doesn't
get broken any further.

The bad news is that either the CF adapter or the CF card itself does not work.
Initially, on booting the machine, it beeped once and then halted on the boot
screen. I attempted to boot the computer from the CD drive, but it seems that
the BIOS is incapable of booting CDs. I wasn't sure of this at first, since I
had no indication that the machine was even working after the initial beep, but
I found a user guide on the web (which I will list at the bottom of this
document) that gave instructions for accessing the self-test functionality and
other BIOS options (power off the machine, then hold F1, then power it on while
still holding F1, and hold it until the options screen appears.)

It was in this options screen that I saw that there was no option for booting
from the CD drive in the boot order configuration, and more research confirmed
that it is not possible.

After that, I ran all the machine's self diagnostics to see if everything was
still functional. All the copmonents passed except the disk drive.

I still wasn't sure if it absolutely could not use the CF card, but I did know
that it definitely could not boot from the CD drive. I decided to try putting
the CF card into another machine, and using a VM to install NetBSD onto it
there. Using a CF-to-USB adapter, I created a virtual disk in VirtualBox which
pointed to the physical device.

Installation went smoothly, but after rebooting the VM, it was unable to boot
from the CF card. I initially thought this may be a problem with the partition
size (it is a 16GB card,) so I tried again, but with a 1GB partition. However,
NetBSD was still unable to boot from the CF card in the virtual machine. Just
to be thorough, I tried putting the CF card back into the ThinkPad, but it did
not boot either.

I still don't know if there is a problem with the CF card itself or if the
adapter is faulty. More research showed that some old computers cannot boot
from large partitions or large drives, so maybe its capacity is too high. CF
cards also have an internal flag marking them as removable media, which causes
some BIOSes to refuse to boot from them. Industrial CF cards apparently don't
usually have this flag, but neither do SD-to-IDE adapters. SD cards aren't
native ATAPI devices like CF cards, so the adapter actually has to convert the
ATA commands. Since they are made specifically for hard drive replacement, they
apparently don't set the removable flag either.

In light of all this, my plan now is to obtain the following things:

1. A 2GB SD card, and possibly also a 4GB SD card. The ThinkPad originally
  shipped with 2 and 3GB hard drive options, so I know it can handle 2GB, and
  I'm hoping it can also handle 4GB. It might be that only the partition size
  is a problem, and not total capacity, but I want to rule it out just in
  case. I have larger SD cards anyway if it turns out it is a partitioning
  problem.
2. An SD-to-IDE adapter. I actually already have one of these, but it is for
  the larger desktop IDE connectors, and I need one for the smaller laptop
  size. I do know that my current one works, since I was able to install
  NetBSD onto an SD card in it on a slightly newer desktop computer. I plan on
  using that computer and adapter to install NetBSD onto the smaller SD card
  if I can't figure out how to boot directly into the installer on the
  ThinkPad.
3. The original internal floppy drive for the ThinkPad 760 line. I'm not even
  sure if NetBSD can be installed from floppies, but having any bootable drive
  that isn't the hard drive will probably be helpful. At the very least I
  might be able to install FreeDOS. Luckily, I was able to find an eBay seller
  in Germany selling brand new internal floppy drives, complete with the
  plastic shield that makes it flush to the laptop's case.

I have some final notes about why the CF-to-IDE situation might not be working.

First, I noticed that the adapter does not fill all the pins on the connector
inside the laptop. There are four pins on the far right that are not populated
when I plug it in. I don't know yet what these pins are for, but maybe they are
necessary for bootable drives.

Second, inside the case, below the hard drive bay are four springy metal
contacts. It seems that they would have been in contact with the metal case of
the original drive, since there is a cutout in the plastic holder right above
them. I'm wondering if the ThinkPad uses them to somehow detect if a hard drive
is actually present or not based on whether they are shorted together. If that
is the case, I might need to insert a small piece of metal to connect them, but
I'm hestitant to try deliberately shorting anything until I find out exactly
what they are.

Anyway, as I said before, there would certainly be difficulties in getting the
old machine working again, but I am still confident that I can bring it back
into useful operation, even though I haven't actually been able to install an
OS on it yet. The BIOS diagnostics indicated that everything is working, and
now that I have a power adapter for it, I can test whenever necessary. Since it
apparently accepts such a wide range of voltages, I am confident that even if
the current adapter fails, I could easily make a new one using a different
charger soldered to the original plug. Hopefully I will have better luck once
the new parts come in. And besides, it wouldn't be real computer work if
everything just worked the first time.

Here is the user guide website with all the information about accessing the
BIOS menus, among a lot of other things:

https://conradshome.com/thinkpad/760_userguide/

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