I have come to notice that the different models of “normal” C64s can cause some confusion. Special models and different casings aside there are two main versions of Commodore 64 – the original hardware design and the new, cost reduced hardware design. There are some differences between these two designs and the greatest difference is the SID chip. Original motherboard design has the 6581 SID chip and the new model has 8580. These motherboard designs comes in the various casings all mixed up.
C64 C models can have either motherboard version. A C64 G will most likely have the new “short” motherboard – it’s not 100 % sure however. The brown “breadbin” C64 is always assembled with the old “long” motherboard.
Not only the SID chip but almost the complete chipset has been replaced with new ones in the new motherboard design. The new chips run cooler and thus are less likely to fail. For most part they are not interchangeable with the old chips. Some of the new chips run with lower voltage, so the new motherboard can draw more current on the +5V line. It’s not adviceable to use the old C64 Power Supply unit with a new model motherboard because of the difference in rating (1,7 A vs. 1,5 A in the +5 DC line).
The model C64 C is likely to cause most of the confusion as these are very common and can have either the new or the old motherboard inside. A 100 % sure way to know what’s inside is to have a look.
C64 C with old “long” motherboard. Fuse and keyboard connector highlighted (read below why).
If you can’t or don’t want to open up the machine you can have an educated guess by looking at the keyboard.
According to my experiences C64 C models with the old style key prints have the old motherboard. This is not a sure proof however, because Commodore has been manufacturing the machines in “what do we have in the storage today” style. Also, it’s very easy to swap motherboard or keyboard between the different models.
To check the motherboard (and SID) version look into the Expansion Port. Spot the fuse and check its orientation (see the above motherboard pictures). If you can see the fuse from its side, it is the old motherboard design with 6581 SID. If the fuse is pointing at you, then it is the new motherboard version with 8580 SID chip.
This is the User port of a C64 C with old motherboard. The keyboard connector is located at the far opposite end of the motherboard.