Commodore PC-40 III

Facts

  • Type: Home computer
  • Manufacturer: Commodore
  • Released: 1989
  • OS: Commodore MS-DOS
  • CPU: 80286 @ 12 MHz
  • Memory: 1 MB RAM (640 KB + 384 KB)
  • Video: VGA (256 KB RAM)
  • Graphics: VGA 320×200 (256 colors) to 640×480 (16 colors)
  • Audio: PC speaker (1 bit)
  • Internal storage: 40 MB 3.5″ PATA/IDE hard drive
  • Removable storage: 5.25″ (1.2 MB) or 3.5″ (1.44 MB) floppy drive
  • FPU: Optional 80287
  • Expansion slots: 3 x ISA-16, 1 x ISA-8
  • Predecessor: Commodore PC40
  • Successor: Commodore PC50

Released 1989: The Commodore PC40-III is a home/business desktop computer in the range of Commodore International’s IBM PC compatible line. It’s an IBM PC AT 286 clone running at 12 MHz, it came with an 40 MB hard drive, and usually an 5.25″ or optionally an 3.5″ HD floppy drive and 1 MB RAM (640 KB base/384 KB hi-mem) and a socket for optional FPU. It also got VGA graphic integrated on the motherboard.

Background history: In 1984 Commodore signed a deal with Intel to second source manufacture the Intel 8088 CPU used in the IBM PC. In 1987, the first model in the IBM PC compatible line was released, the PC-10.

Incompatible with their Commodore 64/128 and Amiga architectures, they were generally regarded as good, serviceable workhorse with nothing special, but the established Commodore name was seen as a competitive asset. I remember Commodore PC clones being used in offices in the company where I worked during school summer vocations  etc.

Design features shared with Amiga computers:

  • PC40-III got a separate mouse port for using an Amiga compatible mouse “A1352”, which can’t normally be used on a PC, this works with the normal Microsoft mouse driver.
  • The 3.5″ floppy drive can be set by a jumper to “DFO” and then be used in an Amiga computer.
  • I noticed a similarity with the Amiga 2000/2500 computers in how the drive cluster and power supply unit sits on a rack above the mother board.
  • The power connector to the main board looks like the very same type used in the later Amiga 4000 (1992).
  • The BIOS setup looks exactly like the one used in the Commodore PC emulator cards for the Amiga, like the A2088XT emulator card or the A2286AT emulator card.

PC-speaker output: The PC40-III got a RCC plug for PC-speaker output on the rear, I think they added this just to fill in a hole in the chassis. The hole is there because some earlier models in the line used the same chassis, and they had an integrated CGA graphic with RCC plug for RGB output.


Repair

PC40-III got the CMOS/RTC battery integrated in a chip “Dallas chip”. The Dallas chip was common back then, and when the non-rechargeable battery within the chip wears out, the settings are lost, and there is no way for the computer to recognize and boot from an hard drive any more.

Different to the Compaq Portable III computer I’ve worked on before, the chip is soldered onto the main board, no socket. I decided to save time and “modify” this chip without removing the chip first.

I used a carpet knife to carefully scrape holes exactly where the ground and plus for the battery are located (above pin 16 and 20 I think). I cut the ground feed leading to the integrated battery and soldered on a coin cell holder for a new 3 volt coin cell battery.

Dallas chip, fix battery
Dallas chip with dead CMOS/RTC battery, fixed with a new coin cell battery.

Success, the computer now works,  CMOS/BIOS settings and time are saved, importantly it’s possible to set the correct hard disk type in the the BIOS settings. Luckily the original 40 MB hard drive still worked. I used MSDOS FDISK to setup an partition and then formatted the disk with “format /s” command.


Commodore PC40-III

Remi Jakobsen


I'm collecting classic computers and video games, stretching from the 70's into the 90's. Restoration, history, usage ...


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