Several years ago, I got hold of a Commodore SX64. Having it for so long, but now I finally came around to restore it and make it the ultimate one (for me at least). I didn’t want to do much on the outside and make all the mods reversable. The stock SX64 (or C64) was very complete and it had all the original stuff (most notable the blue caps and keyboard cable), but I added several additions and ‘upgrades’ to it:

• Replaced the builtin CRT with a TFT module
• Multiple Kernals
• Multiple DOS and (external/internal) parallel cable
• Internal SD2IEC
• Internal MagicDesk cartridge
• switchless switcher with status display

The replacement of the internal CRT with the TFT is pretty straightforward. As there are several tutorials around on the internet, I won’t go in much detail here. I used a 5.6″ TFT (type JD567M03/AT056TN52 V3) from AliExpress and a 3d printed mount for it on eBay . Note that I’m not affiliated with any of these sellers, but they were a perfectly fit. The composite video signal is found on pin 4 (signal) and Pin 2 (GND) on connector P16.

As the internal monitor assembly also housed the speaker and its amplifier I needed a replacement. I used a 3W 8002 mono amplifier chip I had lying around and designed a small breakout around it. The audio signal is found on pin3 (signal) and pin 4 or 5 (GND) on connector P18. The TFT replacement provides plenty of extra room for a extra mods.

To control all the new features it features a control board that houses the KERNAL and DOS switcher. It is loosely based on the Bwack switchless kernal switcher but uses a more powerful ATMega328PB chip. This one has more pins and can control all the mods inside. The original kernal is replace by a 27C040 which can hold all known (to me) kernals.

A custom designed SD2IEC (Larsp variant) fitted there to give a more reliable storage to the old computer and ahs the same footprint as the controlboard.,. A micro-SD extender cable is carefully routed into the glove compartment to provide a more easy access to the micro-SD card. The cable wasn’t working properly at first but a quick google revealed that the removal of a small resistor will solve this issue. The control board switches the device IDs of SD2IEC to 8 or 9 and the internal 1541 to 9 and 8.

The internal 1541 drive is fitted with a board that has a CPLD that couples a large EPROM (27C040) and an extra RAM (621024) into its CPU. The design is based somewhat on 6502 RAMROM and its predecessor PETRAM (seems to be offline now). It is capable of running Stock, (S-)Jiffy, Speeddos, DolphinDos and 64’er. Due to it simple nature it does not support ProffesionalDos and Flash! as those speeders need extra hardware and/or different connections to the C64/SX64. Not a big deal as (S-)Jiffy and DolphinDos are IMHO the best speeders. the control board selects the right memory configuration over a SPI interface.

As some of the diskspeeders need a parallel connection between the computer and drive, I designed a combined PCB with an internal and external parallel and 6522 breakout as well. I decided not to use the internal one as I have also a WiFi ‘modem’, EPROM programmer(s) and an IC tester that can use the user port. Also it can be unplugged with a incompatible kernal/DOS to prevent damage to the CIA and PIA chips.

The SX64 has a small but hidden CRT control behind a door on the front panel. The original board was removed and replaced by a custom PCB. This PCB has a 4x a 7 segment displays to show which Kernal is active, the driveID of the internal disk drive and whether the sound is muted. It also has a button for quickly revert to stock SX64 Kernal and another to quick reset the machine. Two other buttons let you cycle through the D64 images on the SD2IEC and the remaining two LEDs shows the status and activity of the SD2IEC module. To make it simple I used a TM1651 chip, salvaged from a Gotek drive) handles both the display and switches.

To add ultrafast load of your goto programs an internal MagicDesk cartridge is added which provides upto 512K of readonly space. This one is featured long time ago here.

As much as I like the current setup, I made sure to keep the original parts I replaced in order to revert all the changes (except for the original PLA as that one broke down and not having the original SX kernal). I also have spare PCBs of the several parts of this built, please drop a comment if you are interested.

In the next blogposts I’ll highlight some of the mods.