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The creation of the 64 Tuning Board (Article)

When the Modular64 was not yet completely finished, but was already working, a new idea came around the corner in my head: 

The "64 Tuning Board"

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:

  1. Tuning HAT Placeholder 
  2. 3 x SID socket 
  3. 3 x SRAM socket 
  4. 3 x I2C ports 
  5. 2 x Keyboard ports 
  6. Kernel switch via restore button 
  7. Kernel switch via jumper 
  8. Char ROM switch via jumper 
  9. Userport Parallel Cable Connector 
  10. Video modulator slot 
  11. Soft and hard reset option 
  12. Stripe Fix 
  13. Pi1541 Zero Socket 
  14. SD2IEC Socket 
  15. SDCard Placeholder 
  16. Userport 9V/12V option 
  17. PAL/NTSC switching function 
  18. Direct LUMA bridge and jumper to modulator 
  19. Measuring points for almost all signals 
  20. Socket slots for relevant address lines 
  21. RGB LED as power LED replacement 
  22. TOD frequency can be set via potentiometer 
  23. Jumper for internal colour RAM option of the 352525 IC 
  24. Stereo audio amplifier circuit 
  25. Audio mono jumper option 
  26. 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. 

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