All I wanted to do was replace the battery.
I have a Toshiba PORTABLE computer from 1989. These cost about $10,000 when they first came out. Mine is pretty suped-up. It has 14MB RAM (6 RAM cards) and runs Windows 95. Big Hard Drive, too, for that era: 200MB. And a floppy drive, of course.
The built-in display is an orange plasma screen, but there is a color VGA output with its own dedicated 256KB of video RAM. It uses a serial mouse.
It is missing a few key things, though. First the 30 year old battery for CMOS is dead. There is no sound card, just a speaker. It has a modem card but no networking/LAN card. And there is an empty socket for a 80387 Co-processor for floating point arithmetic, aka, an FPU.
BIOS
There are two memory chips in sockets. I believe I am looking at the BIOS. You could upgrade by pulling one out and putting in a new one. This was also common on synthesizers in the 80’s. Firmware on an EPROM in a socket on the main board.
One is an AM27C1024-200DC. These are made by AMD and available today. This specific one is a ceramic IC in a 40-pin DIP configuration, The memory access speed is 200 microseconds, and it stores 1 megabit. It has a sticker covering the window for programming (it is an ultraviolet EPROM). This is the BIOS chip, since the system diagram says the BIOS ROM is 128KB, which is 1 megabit (and the motherboard label says so!).
The other 40-pin DIP in a socket is an Intel 8-bit microcontroller, the D8749H from 1980. Old reliable! It is labeled SCC but I don’t know what that is. It also has memory and is an EPROM. Just discovered it is the Keyboard Scan Controller.
Expansion Slots
There are three expansions slots. A Toshiba slot, which has a modem card in it and an AT and an XT slot. The AT slot is the original name for the ISA slot (and it is 16-bit). It is on top. The XT slot (about half as many connectors) is now called an 8-bit ISA slot, and it is in the middle. Only the Toshiba slot (a T3100 expansion slot on the bottom) OR the 8-bit slot can be used at the same time due to space constraints.
The Intel 80386 CPU
Type Central processing unit / CPU
Family Intel 80386
CPU part number A80386DX-20 IV
Introduction 02/16/1987
Manufacturing Date 30th week of 1989
Package 132-pin CPGA
Dimensions 36,8 mm x 36,8
Manufacturing process 1000 nm
Transistors 275000
Frequency 20 MHz
Data width 32 Bit
Floating Point Unit (FPU) None / 80387 capable
Power consumption 1 Watt
Vcore 5 Volt
This model CPU had a notorious bug that prevented them from working properly using 32-bit software. The system would freeze up. Intel tested the chips and marked the good ones with two sigma characters. The bad ones were stamped “16 bit s/w only,” since they worked fine with 16-bit operations. My chip has the double sigma markings.
Notice there is no FPU. These were integrated in the 486. The 80387 is easy to find on ebay, so I ordered one. Just make sure you match the MHz of the CPU, which is 20 in my case. Watch the orientation of the FPU when installing. One corner is cut at an angle by Pin 1. On the motherboard Pin 1 is marked with a yellow circle as shown below.
I wonder how I will be able to test if it works? I can’t find anything in the manual about installation (though physical installation is simple), but some sources online suggest a jumper or BIOS setting maybe required. Others on Facebook say no, it should just work. After powering on the system, it recognized the 80387. I will do some more testing, though, for fun and learning.
This document has great information on FPU’s:
https://mikro.naprvyraz.sk/docs/Coding/Hardware/COPRO16A.TXT
Some more info on an FPU upgrade: https://kb.iu.edu/d/aanp
This Old Floppy
I tried to run some benchmarks from a floppy but could not boot into MS DOS. I tried another disk just in case the first was bad, but none worked in the floppy disk drive. This is a bit of a problem, since it is a very old floppy and does not have a standard floppy pin header, nor does the motherboard. The solution is to either find a very rare (and old) floppy or make a new cable, as others have done, that adapts floppy drives with a 34 pin header into the 26 pin header on the motherboard.
Other possibility- maybe I have to format the disk on the Toshiba? Seems odd, though, but easy to check. I can also try to clean the heads. There used to be floppies that were head cleaners (the disk was replaced with a cleaning disk); in fact, Amazon sells them.
So I cleaned the heads and also tried formatting a disk. Nothing works. The floppy disk window opens when a disk is inserted, the platter motor works, and the stepper motor works. I confirmed this by moving the head assembly then starting the computer. It sent a signal to the stepper to move the read/write heads back to the boot sector location (which is on the outermost disk, track 0).
I have decided to do a little more digging into the old drive. I have disassembled it more and found an oscillator and two electrolytic caps. Everything else is surface mounted and I won’t mess with them. I will power the floppy up through a breadboard and check the oscillator. This is really just for fun since I have no schematics and really no chance of fixing this old floppy.
The breadboard is fed from a standard wall ac/dc adapter at 9v. I run the power into a 7805 (5v voltage regulator) to get the proper power. I inserted header pin strips into the breadboard so the floppy could simply plug in to it and get power.
Rabbit hole alert!! All about floppies: http://www.philipstorr.id.au/pcbook/book4/floppyd.htm
Wiring Up a New Floppy
The Toshiba manual is awesome and has the pinout information for all sockets on the motherboard. Here is the floppy disk drive information that will let me make a new cable or use jumper wires to install a 34-pin floppy if needed.
Now to map these terms to those in a 34 pin floppy pinout, shown below. This drive only uses 5v- I tested each pin labeled Vcc and they all had a good 5 volts as expected. The names for what each pin do is a little different, but luckily a really smart guy on Vogons published a mapping and I just had to do the work right.
Notice that none of the odd pins are shown below- that is because they are all (most*) connected to ground so no need to list them.
On my model floppy I found that pins 1, 3, 5 are not connected to anything so don’t try to use these for ground.
I found the complete mapping from 26-34 pin drive on the Vogons website, made by someone who did some great mods on this same model computer.
Motherboard pins to new floppy
- 2 -> 8
- 4 -> 12
- 6 -> 34
- 10 -> 16
- 11 -> 2
- 12-26 (even) map in order to 18 – 32
- 8, 9, 13-25 (odd) go to ground (any of odd pins 7 – 33)
Pin 9 is a special case. Grounding it means the system will work with 1.44MB floppies, which is all I need. Pins 1, 3, 5, 7 from the motherboard can be ignored (they provide 5 volts), since I am getting power off the hard drive power cable.
Power to the Floppy
Now, is 12v and 5v used in a floppy? It depends. In mine, I need 12v and 5v so am splitting power off the hard drive cable and running it to a floppy 4 pin connector (these carry 5v and 12v, with two ground pins in the middle). The color coding for hard drives and floppy drive 4 pin connections is as follows:
- red – 5v
- black – ground
- yellow – 12v
Worth noting that securing the Dupont cables to the pins required using E600 craft glue. It dries hard but can be peeled off.
The “New” Floppy Works
I fired up the system and the new floppy works great. I can now boot the system from a floppy into MS-DOS 6.0 and use the floppy drive. to load other software, like drivers for an ISA SoundBlaster card!!
Benchmarking- Finally
Phil’s Computer lab has a nice suite of benchmarks for retro gaming machines, but I have no way to put the larger ones on the Toshiba, since the only way I can copy files to it is via floppy and I am really not interested in splitting a larger file across 10 floppies. Luckily, most of the benchmarks will fit on a floppy (just the Doom and Quake benchmarks are too big), so I will be able to give it a shot and provide results. Maybe one will indicate the FPU is present!
I also got to run some benchmarks on the system and found one that compares the CPU and FPU to a 80286/287 reference standard (The IBM AT Computer). The test provides a score in equivalent Mhz to the AT., which is a little odd. Mine now comes in as a 34Mhz 286 and a 51 Mhz 287. It you look up the clock speeds for an AT, you will see 6-8 Mhz for the CPU and 8-12 for the FPU. The 386 is much faster- about 6 times for CPU and FPU. I also ran a video test and got a whopping 7.6 FPS compared to 212 on a 1GHz Pentium 3. Memory speed came in at 8 MB/s for reading and 15 MB/s for writing. The memory tests also correctly discovered that the CPU has no cache.
Video Benchmark 
Toshiba Diagnostics
These programs (for use from a floppy, I think) would be handy to find and includes tests for all the major IO systems.
Networking
I don’t know about this one. I need an 8-bit ISA card. So far I am only seeing ones with a BNC socket and a 15 pin socket, like for a gameport. Some of the cards are Token Ring, which won’t help. I am probably asking for too much. Yet I found someone far crazier than me who is building MODERN versions. https://github.com/skiselev/isa8_eth
Battery Replacement
I had to take the entire computer apart to get to the battery. Really. Incredible pain, but that is also why I am writing all of this up. The new battery wires were too short and they were connected to a two pin plug. The motherboard has a three pin plug, so a little cutting and a little soldering to swap plugs and I had a new battery cable and everything installed.
ISA Sound Card
I had a Sound Blaster 16 ISA card lying around for another build, but decided to pop it in this computer instead. It worked perfectly in DOS upon initial install of drivers but not in Windows. There were a few problems. One, there was no autoexec.bat file so no place for the driver install/configure process to write sound blaster environment variables.
The other problem was that the installer for the driver bundle did not copy all the required files to the C:\Win95\System directory. I discovered this when looking at the Driver tab for the sound card in Device Manager. The tab shows a bunch of driver-related files and information on each file as you highlight them. However, I noticed several did NOT have any information being shown and when I looked in the directory I saw they were missing. I re-ran the driver exe (it is a self-extracting installer than has driver files in it) I downloaded from Phil’s Computer Lab (https://www.philscomputerlab.com/creative-labs-drivers.html) and copied the missing files to C:\Win95\System. These steps solved my problems and I was thrilled to hear the Windows95 startup sound, created by none other than Brian Eno.
I still have to test MIDI files in Windows, but audio (wav) files work fine.
More Legacy of the 386
This was the first 32-bit in the Intel x86 family.
https://en.wikipedia.org/wiki/Real_mode
Very Cool Resource
https://discover.hubpages.com/technology/How-to-build-an-awesome-386-computer-Part-1-The-Hardware
Erich Izdepski 