Assy 250425 Rev. A

This is a Version B motherboard produced from 1984. Numerous chips surrounding the VIC-II (MOS6569) graphics chip have been replaced by a single clock generator IC (MOS 8701). The locations of the SID (MOS 6581) and the PLA (MOS 906114) have been swapped with respect to Version A-CR.

The inside of the machine:

All electrolytic capacitors and voltage regulators have been exchanged for new ones as described in the C64 Capacitor Mod.

The CPU, the VIC-II, the PLA and the SID chips all have heatsinks attached to keep them running cool. Heatsinks and thermal tape have been bought from the spares shop.

Capacitor C38 (51 pF) has been replaced by a 4.7 nF one to make the RESTORE key work like all the other keys as described in the C64 RESTORE Key Mod.

The outside of the machine:


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10 thoughts on “Assy 250425 Rev. A”

  1. I have one of these, made in England…. unfortunately … black screen. Occasionally I can get a garbled image…

  2. It sounds like you may have issues related to the PLA and/or Character ROM’s. I’ve had a similar problem with a long board motherboard (link)

  3. What does the switch on the RF modulator do? I only have the RF cable to connect to my TV and I’m wondering how this switch effects video/functionality. Also can anyone recommend anything to improve picture quality, that doesn’t need the Commodore video cable or a modification to the board?

  4. A year later… The switch changes from channel 3 to 4 normally in the NTSC version. You can build your own S-Video cable is not hard some soldering skills needed. That will make the video a LOT better. You can also find the cables pre built on e-bay

  5. Hi Jeffrey, well there is not really much difference between the two board revisions. AT least not to my knowledge 🙂 If you know of any, please let me know, OK?

  6. I have a 250425 board with broken leak stuff on the board. Is it possible to buy a SixtyClone board and move things over ?? and what board would I use as it only comes in three variants…250407/250466/250469 ??

  7. Hi CloneBoi, The closest SixtyClone board would be the one of the long boards: Assy 250407 or the 250466. However, if you choose to go with the 250466 board you would obviously need to buy different RAM modules. Regardless of what board you choose, you could consider buying some of the cheaper parts (resistors, capacitors, transistors, diodes etc.). This will reduce the risk of adding dead parts to the new motherboard due to the desoldering process 🙂

  8. Only difference that I can spot between rev’s is that rev B have additional disc capacitor, without silk screen designation on left side of MOS 6569R3, next to C15

  9. I’m currently working on a 250-425 board, and it’s dad but displaying some characters on the screen in the proper colors.
    Been playing around with the board the 6581 chip cause the sound to make an odd click noise when you press on it. I pulled it cleaned up the tabs with deoxit along with the socket and I also noticed one pin on it was bent over. I straightened it out carefully got it back into the socket but it still displays virtually the same image.

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