Upgrading the V86P HDD Controller
Back in a previous post I set about reverse engineering the HDD controller, and one of the things I was able to work out was the pinout of the connections to the mainboard. In fact, I commented that this looked like a stripped-down ISA bus with only the necessary signals being routed through - a fact confirmed by the system interface IC on the controller. I think I mused at the time at the possibility of fabricating a board that fits where the existing controller goes, but contains an XT-IDE (for those unfamiliar, this is an open-source IDE controller for 8-bit ISA systems that allows the use of regular IDE/PATA drives). In my last post, I documented my work with the expansion bus and testing with a regular 8-bit ISA XT-IDE card - which worked perfectly, with the exception that the top 384k of RAM (normally available via EMS) has to be disabled because there were conflicts with the default ROM location of the XT-IDE's BIOS. Pulling the internal controller and relocating the ROM location should address this.
Recreating the V86P Floppy Drive Riser
One of the things I remember from my original V86P back in the 90s is the way the floppy drives connected to the motherboard. The two drives were mounted back to back, with a riser card between them that connected to a socket on the bottom of the motsherboard. One of the things that would happen after a while is that one of the drives would rattle slightly loose and become disconnected - and thus stop working. The quick fix was to put a disk in both left and right drives and push inward on both disks at the same time - thus reseating the drives back on the riser card. Looking back, and comparing to my current system, I suspect my original system might have been missing one or two of the studs screwed onto the side of the floppy drive, securing it from lateral movement by engaging in holes in the metal battery enclosure.
Working on the V86P expansion bus
If you remember from this post, I'd previously reverse engineered the expansion interface pinout on the back of my V86P laptop and determined that it looked just like an ISA bus, but with the voltage rails removed (and replaced by grounds), with one exception that was connected to the 5V rail via a pull-up resistor. I'd mused at the possibility of building a board to let you hook up a regular ISA card - and that's exactly what I decided to do. Part of the motivation was to try connecting up an XT-IDE to hook up a more modern hard disk, thus allowing me to make a backup of the existing drive, and also to make it easier transferring data onto the laptop. What's more, once I'd confirmed the XT-IDE worked without issues, I could set about potentially replacing the internal hard disk controller.