• Type: Home computer
  • Released: 1984
  • Introductory price: ~$299
  • Discontinued : 1985
  • OS: Commodore BASIC 3.5
  • CPU: MOS 8501 @ ~1.77 MHz
  • Memory: 64 KB RAM
  • ROM: 64 KB (Commodore BASIC 3.5 with machine code monitor, and TRI-Micro's "3 Plus 1" (word processor, spreadsheet, database, graphing))
  • Graphics modes: 160x200 (multicolor) / 320×200 (hires)
  • Sound: TED chip (2-channels)
  • Text mode: 40×25 characters (PETSCII)
  • Palette: 121 colors
  • I/O: Tape connector (incompatible with C64), cartridge slot (incompatible with C64), IEC port (compatible with C64), User port (for modems and nonstandard devices, incompatible with C64), Composite video connector including S-Video and mono audio signal, RF modulator

Released 1984: The “Plus/4” name refers to the four-application ROM resident office suite (word processor, spreadsheet, database, and graphing); it was billed as “the productivity computer with software built-in”. Internally, the Plus/4 shares the same basic architecture as the lower-end Commodore 16 and 116 models, and is able to use software and peripherals designed for them. It is not compatible with the well-established Commodore 64. The Plus/4 was the flagship computer of the 264-series. The Plus/4 had 64 KB of memory while the C16 and 116 had 16 KB. The Plus/4 had built-in software, whereas the others did not. Worldwide, about 827.000 units was shipped, about 286.500 alone in Germany.

According to what I’ve understood from Bil Herd, ex. Commodore hardware engineer. New management in 1984 first misunderstood the 264-series and the Commodore 116, that was supposed to be a competitor for the marked segment of very cheap home computers, in the price range 50-75 USD. They ordered the Plus/4 and it stepped on the C64 toes in price range and confused the marked a bit. And it all landed on the C16.

My Commodore Plus/4 and repair
There was no display when I first got it. It’s a very common failure that either CPU or TED chip fails. The case is very small, and this results in heat that affects the reliability over the years. Those two chips was only used in the 264-series (C16, C116 and Plus/4), so they can be both difficult and a little expensive to come bye. I first replaced the TED chip, and it didn’t help. Then I replaced the CPU chip, and this time it worked. (CPU is probably the most common chip to fail and cause black screen, so I should have replaced that one first.) I also put heat-sinks on the chips before putting the machine back together.

SD2IEC floppy drive emulator works with this computer as well, only had to solder in a correct connector to take current from the cassette port. It got a different cassette port connector than the C64 and other Commodore 8-bit computers.

Commodore Plus/4

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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