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 Numerous chips surrounding the VIC-II (MOS6569) graphics chip have been replaced by a single clock generator IC (MOS 8701).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 (link).
The MPU is a MOS 8500 and not the MOS6510 that is usually found on longboards. The MPU is produced in week 51 1985 which is the same as most of the other chips and it does not seem to have been replaced. So this may just be another example of Commodore using whatever parts they had in stock.
Capacitor C38 (51 pF) has been replaced by a 4.7 nF one to make the RESTORE key work like all the other keys as described in the C64 RESTORE Key Mod (link).
The outside of the machine:
© breadbox64.com 2017
I have one of these versions of PCB, but it’s in a C64C style case. I also have this PCB in a bread-bin case, so I thought this was just somebody swapping the case at some point. Last week I purchased a Commodore job lot off Facebook Marketplace and to my surprise there is another one (Assy 250425 in a C64C style case).
There are a few differences in the case between these versions and my genuine C64C (250469);
1. The serial label underneath is very basic and just says C64 Ser-No xxxxxxx.
2. The case does not have any screws, it clips together.
3. The keyboard clips into the top of the case rather than resting on 2 metal mounts on the base. Does anybody know if this was an official Commodore version?
Or was this some local computer shop performing case upgrades??
Hi Gary, I have never heard of the case that you describe. Sounds like a third party version of some kind… Finding Assy 250425s in a slim C64C case is not uncommon and is most likely related to Commodore just using whatever parts they had on the shelf 🙂