Three precision sockets were soldered in to easily swap the Basic, Kernal and Characters ROM ICs. The middle IC (the Kernal ROM) have been replaced by a small PCB (switchless kernal) with both the original Kernal and JiffyDOS included. Pressing the RESTORE button during power up will boot the system into JiffyDOS. If nothing is pressed during power up, the machine boots into the standard CBM Kernal. Again nothing can be seen from the outside of the machine.
To get the switchless Kernal PCB to work, one cable must be soldered to the RESTORE signal on the motherboard while the other wire goes to the reset signal (pin 40) of the MPU (MOS 6510). The specific solder points can be seen in the pictures.
All capacitors have been replaced as described here. This should make them work for another 30 years without drying out. To be consistent with the idea of replacing all standard electronics which may fail over time, the voltage regulators were also replaced.
To keep everything as cool as possible I’ve also added heatsinks to all large ICs (SID, MPU, VIC-II). Heatsinks and thermal tape have been bought from the Retroleum.co.uk spares shop.
The board had a black screen at start up when I first got it. It was easily fixed with a new PLA chip (MOS 906114) at U17. The PLA is a new design that I got on Ebay. Contrary to the original PLA, this one runs cool.
On the old long boards of the Commodore 64, the RESTORE key needs to be hit really hard to function due to a misdimensioned capacitor at C38 also known as the ‘NMI Capacitor’. On the new short boards, the problem was fixed. If the original capacitor of 51 pF is exchanged by a 4.7 nF one, the RESTORE key functions as well as all the other keys of the keyboard. The capacitor at C38 was replaced as described here.
An orange LED was added to the case as described here. The orange color actually looks a lot cooler in real life…
And that’s it! Hope to see you back in 2016!
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