RetroTechCollection

SixtyClone Bare-Board Project

The SixtyClone bare-board project is an open-hardware effort to recreate every major revision of the Commodore 64 logic board as brand-new, professionally-fabricated PCBs. Designed so that hobbyists can transplant the original MOS/CSG chips from a corroded or broken donor machine into a fresh board, SixtyClone provides a legal, royalty-free alternative to scavenging vintage hardware. The gerbers (and KiCad sources for recent revisions) are released under a permissive licence; commercial runs are sold via Bob’s Bits on Tindie and by several regional group-buys.

SixtyClone “Bare-Board” Project
Caption Green-solder-mask SixtyClone 250407 replica PCB (rev b)
Type Drop-in replica Commodore 64 mainboard (bare PCB only)
Designer “Bob’s Bits” community project (lead: Rob Taylor)
contributors incl. Jim Drew, Leif Bloomquist & C64 enthusiasts world-wide
Manufacturer Unknown
First released late 2016 (initial 250407 gerbers uploaded)
Latest revision rev E gerber set (2022) – 250407, 250466 & 250469 variants
Operating voltage —
Layers / PCB 4-layer FR-4, ENIG finish, gold fingers
Compatibility 100 % electrical* with original C64 ICs & shields
(*one bodge wire on early rev A to route VIC /Φ0)
Features • modern 4-layer impedance control
• enlarged silkscreen legends & test-pads
• optional dual-kernal footprints + JiffyDOS jumper
• consolidated decoupling network & “silk-BOM” printing
Model No. SixtyClone-250407 / -250466 / -250469

Project goals

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  • One-to-one electrical compatibility – keep every trace, pad and via placement true to Commodore’s own artwork so that RF shields, heatsinks and cartridges still fit.
  • Manufacturability upgrades – convert the 1980s 2-layer stack-up into a modern 4-layer with internal ground/power planes which greatly reduce crosstalk and audible VIC “jail-bars”.
  • Usability improvements – large white silkscreen labels (including capacitor values) double as a printed Bill-of-Materials; mounting hole diameters match today’s metric M3 hardware.
  • Educational licence – gerbers are free for personal use, encouraging new builders to learn through-hole soldering while preserving classic computers.

Supported C64 revisions

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SixtyClone variant Original Commodore PCB Key differences / notes
SC-250407 “long-board” breadbin (1983-85) Most common donor; retains separate 6581 SID & 12 V rail
SC-250466 late breadbin (1986) Two 4464 DRAMs, 8562/8565 VIC, color RAM integrated in PLA
SC-250469 short-board / 64C (1987-92) HMOS chips, 9 V SID supply; optional pads for dual-kernal switch

Early SixtyClone rev A boards required a bodge wire between VIC pin 38 and the CPU ϕ0 trace; this was fixed in rev B and later.

Bill-of-materials overview

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Because SixtyClone is just the PCB, builders must source every through-hole component:

  • 21× logic ICs (74LSxx), 16× passives, crystal & can oscillator
  • PLA, CPU 6510/8500, VIC-II, SID, two CIAs – taken from a donor or aftermarket replacements
  • three linear regulators & heat-sinks (250407 only)
  • 4700 µF + 1000 µF axial electrolytics (footprints accept radial if leads are bent)
  • DIN keyboard, cassette & power connectors – modern CUI / Cliff equivalents fit the footprint

A colour-coded silk-screen value is printed beside every capacitor and resistor to speed hand assembly. Detailed spreadsheets, Digikey/Mouser links and pick-lists are maintained in the project GitHub wiki.

Assembly tips

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  1. Wash & dry the PCB to remove fabrication flux; ENIG finish is already tinned.
  2. Install low-profile parts first (res-networks, jumpers, resistors) followed by sockets and electrolytics.
  3. Tin the stitched-via grounds under each TO-220 regulator (250407) before mounting the heatsink to guarantee low-impedance bonding.
  4. Perform continuity checks on the 5 V and ground planes *before* inserting irreplaceable MOS chips.
  5. Recommended to pair the build with a modern “C64 Saver” PSU protector when first power-up.

Known issues

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  • SID audio hum – greatly reduced versus original boards but still audible on high-gain amplifiers; adding a ground-lift plane under the audio path (rev E experimental) lowers the noise a further 3 dB.
  • Keyboard bracket height – certain aftermarket metal keyboard braces foul the cassette port shield; trimming 1 mm from the bracket front edge resolves the clash.
  • Case LEDs – early silkscreen marked +/- backwards; always verify polarity before soldering.

Licensing

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Gerber and schematic files are released under Creative Commons BY-SA 4.0. Commercial resale of finished boards is permitted provided attribution remains on the silk-screen and in accompanying documentation.

Availability

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  • Tindie storefront “Bob’s Bits – Commodore 64 replica PCBs” – sells 250407 & 250469 boards in green, blue and black solder-mask, typically US $29 – $35 each.
  • Group-buys on r/c64 and Amibay several times per year, often bundled with complete BOM kits.
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