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MOS CPU Replacer (6510/8501) MOS CPU Replacer (6510/8501) MOS CPU Replacer (6510/8501)

MOS CPU Replacer (6510/8501)

$15.00 inc. tax
Please read the entire description before ordering.
All stock is the latest Rev2 boards.

Replace rare/expensive/unreliable MOS CPUs

  • 6510 (C64) (8500 is same as 6510)
  • 6510T (1551 floppy drive)
  • 8501 (C16, C116, Plus/4) (7501 is same as 8501)
  • 8502 (C128)
The above "CPUs" are just standard 6502s with some extra logic tacked on inside.

This device uses a standard 6502 CPU, and implements the extra functions using discrete logic - no programmable parts.
Standard 6502 CPUs are abundant and cheap, and produced by many manufacturers (Rockwell, UMC, Synertek, MOS, etc).
The 6502 CPUs that I offer with these, are pre-tested.

You can use a 65C02 or W65C02, but this is untested, and will cause compatibility issues with some software at the least, or not work at the worst.
If using a WDC W65C02, you must cut jumper W.

It may struggle to fit inside a C116 or Plus/4 due to height, so for these machines you should solder the 6502 directly to the module's PCB, or solder the module directly to the C116 or Plus/4 motherboard.
For C16, height is not a problem.

It is tested to fit next to a PLA20V8 replacement in a 250407 board. Other oversized replacement boards may interfere and require installing the module in an extra socket to raise it up.

If you order it in kit form, build instructions are on the back of the PCB, and clarified via the Source link below.

Status as of Rev1:
  • 6510 config: Tested working in a C64 and C64C with a wide range of software. In one scenario, it was discovered that it causes graphical glitches when used in a C64 with a C0pperdragon video conversion device (which watches the VIC-II pins). This may now be solved with Rev2, but I don't have the C0pperdragon board to test this.
  • 6510T config: Not tested - I don't have a 1551.
  • 8501 config: Tested working in a C16 and a Plus/4, but it has been found that at least one program crashes on a 64K-modded C16, that doesn't crash with a real 8501.
  • 8502 config: Works but has graphical glitches, likely due to a timing issue, so should only be built if you plan to help me diagnose this. For 8502, you must install a 2MHz-rated CPU (such as 6502A).

Known issues:

  • A local enthusiast has discovered that using this adapter in 8501 config in their 64K-modded C16, results in Slipstream ( hanging, and causing resets to stop working (need a power cycle). One other person has confirmed this, and confirmed it doesn't happen with a real 8501, so the issue is with the MOS CPU Replacer. I will look into possible causes and update this page if a solution is found. Testing the C64 version of Slipstream in a C64 works fine with either a real 6510 or the MOS CPU Replacer in 6510 config.
  • One user reported that it causes graphical glitches when used in a C64 (6510 config) with a C0pperdragon video conversion device (which watches the VIC-II pins), but works well otherwise.
  • I am working on improving the device, and hopefully reaching 100% compatibility. Expect a new version later.

Source files and build instructions

DIY kits have all SMD parts pre-soldered.
Second photo shows a DIY kit with included 6502.
Third photo shows an assembled module with included 6502, installed into a C64.
If you choose to order a 6502 too, they are used items that may come scratched or scuffed - let me know if you specifically need one that isn't.
Product Code: MOS_CPU_Replacer
Product Condition: New
weight: 50.0g
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MOS CPU Replacer
Steve Mason
Sunday, October 8, 2023
Very good mos replacement have tested in c64 and c16, works without fault on any game or Cart I have tried. The build quality is superb and runs very cool on a Mos 6502.
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