At that time I had several 469 boards that had already suffered because of soldering work. In addition, I thought it would be nice to have a C64 board that already had certain features implemented without rebuilding. This would save "flying conversions" (at that time there were no C64 1:1 replica boards, these only appeared a year later).
In the course of thinking about it, I came to the conclusion that if I'm going to change so much, I might as well include everything that's possible:
Measuring points, preparation for ZIF socket, I2C ports, 3 x SID, a "tuning" placeholder for a developer board (Arduino or similar) etc.
Until then, I didn't have a suitable name for the board, but when the "Tuning" placeholder for developer boards was added, it quickly became clear what the board should be called: "64 Tuning Board".
This "tuning" slot opened up unimagined possibilities, as the 16 address lines, 8 data lines, the expansion port signals and several other signals are centrally available here. In the course of this, I later created numerous tuning HATs for it: Midi Interface, Code Injection, Memory Analyser.
The main problem, as with most C64 boards I have built, is the space problem.
This got even worse with the Tuning Board because I took the "short" version as the measure of all things. That limited the space a lot. I also have to admit that it never occurred to me to use a long board as a basis, because my constructions are all based on the 250469 board, which is "short".
This made things difficult. To fit so many chips into such a small space, and then to be constantly confronted with the question of whether it is even possible to connect the tracks, proved to be an insurmountable hurdle. If you take a close look at the finished "64 Tuning Board", you will see that there is not a centimetre of space left. There are tracks everywhere, either on the top or on the bottom.
The feature list shows the lack of Space - Dilemma:
- Tuning HAT Placeholder
- 3 x SID socket
- 3 x SRAM socket
- 3 x I2C ports
- 2 x Keyboard ports
- Kernel switch via restore button
- Kernel switch via jumper
- Char ROM switch via jumper
- Userport Parallel Cable Connector
- Video modulator slot
- Soft and hard reset option
- Stripe Fix
- Pi1541 Zero Socket
- SD2IEC Socket
- SDCard Placeholder
- Userport 9V/12V option
- PAL/NTSC switching function
- Direct LUMA bridge and jumper to modulator
- Measuring points for almost all signals
- Socket slots for relevant address lines
- RGB LED as power LED replacement
- TOD frequency can be set via potentiometer
- Jumper for internal colour RAM option of the 352525 IC
- Stereo audio amplifier circuit
- Audio mono jumper option
- Jumper for video jacks pin 5/7 routing option
This is a good indication of the challenge that was waiting for me.
In the end, however, it worked. But it took months of hard work. One of my most time-consuming jobs ever.
But it was more than worth it. The 64 Tuning Board accompanies me every day, especially for new developments and for testing, because it is the only board with all the necessary measuring points and optional options.