And now, with pleasure, I present the hero of our next quest - the JUKO ST-12 TURBOXT motherboard with 640KB RAM, featuring a NEC V20 12MHz processor and an Intel 8087-2 coprocessor!

By the way, what expansion cards do I have for further start of the motherboard? Interesting cards, but does anyone see a graphics card or a bootable disk controller? I don't see one either(((

First graphics card and first modification

Modification of the Trident 9000I graphics card to work in an ISA8 slot. Cut the trace from contact B28 and add a wire to B29.

Hooray! We now have an image on the screen)))

Hi,

I'm actually reading this thread with interest, I just don't felt the need to comment on it yet as I'm not experienced with NEC V20 CPUs, so I didn't had anything useful to add yet.

However in your last post the modification of the graphics card is a really nice solution to make it work in a ISA8 slot, but from personal experience those pin modifications will become hard to notice when later visually inspecting the card, so to avoid the confusion that I suffered from forgetting one of my similar modifications I would recommend putting a sticker on the card writing down that the pins are modified somewhere for future reference, it is sometimes hard to remember those modifications after some years pass, and it is a good reminder that the card is modified in some way if it will be used in another system.

Otherwise very interesting and nice project 😀

MagefromAntares wrote on 2026-06-03, 06:32:

Hi, […]
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Hi,

I'm actually reading this thread with interest, I just don't felt the need to comment on it yet as I'm not experienced with NEC V20 CPUs, so I didn't had anything useful to add yet.

However in your last post the modification of the graphics card is a really nice solution to make it work in a ISA8 slot, but from personal experience those pin modifications will become hard to notice when later visually inspecting the card, so to avoid the confusion that I suffered from forgetting one of my similar modifications I would recommend putting a sticker on the card writing down that the pins are modified somewhere for future reference, it is sometimes hard to remember those modifications after some years pass, and it is a good reminder that the card is modified in some way if it will be used in another system.

Otherwise very interesting and nice project 😀

Hi!
Tnx for info and interest to my topic.
Trident modification is temporal just to get something on screen as fast as possible
My target is ISA8-only configuration with ISA8 videocard 😀

Let’s take a closer look at the motherboard and examine the memory sockets, ROM chips, crystal oscillators, and jumpers!

1) The motherboard natively supports from 256 KB to 1 MB of RAM.
The exact RAM configuration is specified as a DRAM chip installation diagram in the user manual, and requires proper jumper settings on the SW-A configuration block.

2) There are two sockets on the board for installing ROM chips.
The first socket is labeled 2764 inside the socket footprint and is intended for the primary BIOS 8KB ROM chip.
The second socket is labeled 27256 inside the footprint and is designed for a supplementary 32 KB ROM chip.
(We will return to this one later and try to use it as a BIOS ROM EXTENSION to expand the primary ROM capability and ensure seamless operation with optional expansion cards).

3) The motherboard features two crystal oscillators that determine the CPU clock speed.
In my case, the first crystal operates at 14.31818 MHz, providing a 4.77 MHz clock speed for the CPU in DE-TURBO mode.
The second crystal operates at 24 MHz and gives a 12 MHz clock speed in TURBO mode.
(If your second crystal is rated at 20, 24, or 30 MHz, your TURBO mode speed will be 10, 12, or 15 MHz respectively).

4) The board features jumper J6, which configures the wait state mode: WS0 (0 wait states — a faster operation mode) or WS1 (1 wait state — a more compatible but slower mode for memory and expansion cards).
If parity chips are populated in the memory parity sockets (4 sockets labeled as 21256), the parity check feature can be enabled via the PAR switch on the SW-A block.

Solving the issue with boot devices.

I bought a beautiful multi-card (1xLPT, 2xCOM, 1xGAME, FLOPPY, RTC) in ISA8 format.

In addition to this (since my ISA8 SCSI controller is not bootable), I decided to use the ROM socket on the motherboard (labeled as 27256) as a ROM BIOS EXTENSION and flashed the FUTURE DOMAIN TMC-850/950 SCSI BIOS ver. 8.5 into it.

I am very interested in this project, and I will keep an eye on the progress of this thread.
I have several JUKO motherboards, and I've been struggling with how to utilize them. I use a Realtek 3105 graphics card for display output, which can be used directly without modification.

Meanwhile, I flashed the 8KB Super PC/Turbo XT BIOS 3.1 into a W27E257 EEPROM, and it successfully booted in the 2764 ROM socket!
Furthermore, I inserted another W27E257 (configured as OTP) containing the FUTURE DOMAIN TMC-850/950 SCSI BIOS ver. 8.5 into the second 27256 socket, and it worked as well!

The motherboard is indeed (for now) compatible with 8KB BIOS images in the ROM socket labeled "2764". The following configurations have been tested and verified to work (albeit with some quirks specific to my hardware setup):

1) Native Juko TurboXT BIOS 2.32: It works, but the system fails to POST/boot if any version of the FUTURE DOMAIN SCSI BIOS is inserted into the second 27256 socket.

2) The sleek and modern GlaBIOS (latest version): It works. Upon powering on, the video card BIOS initializes first, followed by the motherboard BIOS. At a certain point, the SCSI controller BIOS initializes and detects the hard drive, but the system fails to boot from the HDD.

3) The equally sleek Super PC/Turbo XT BIOS 3.1: This is currently the optimal choice. It functions exactly as shown on screenshot: on power-up, the video card BIOS executes, followed immediately by the successful initialization of the SCSI controller BIOS, and only then do the motherboard BIOS messages appear. Booting from the HDD works flawlessly.

Expanding RAM to 1024KB

The 44256 dynamic memory chips have arrived (I ordered 10 pcs. as a spare, since many currently sold are refurbished and relabeled). I got lucky and all the chips turned out to be working. Soon we will find out how to use the additional 384KB of memory on this motherboard.

Videocard change and final configuration for today

1) 1MB RAM installed on the motherboard

2) MSDOS boots with 1GB SCSI HDD and Future Domain TMC-850 SCSI controller

3) Soundcard is late Adlib clone

4) Multi-card ISA8 with 2COM, 1LPT, 1GAME, 360/720KB floppy drive interface and RTC

5) Video card Oak OTI-037 ISA8