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Commodore 64K C-116 Mods


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  Commodore 64K C-116 Mods by Bill Degnan - 08/13/2013 14:43
Commodore C-116 Computer
The 1984 Commodore C-116 was the smallest and one of the rarest Commodore computers ever produced commercially.

Commodore C-116 view of original 4116 RAM chips.
NOTE: the original 318004-04 Kernal ROM has already been swapped out, pictured is a 3180005-05 NTSC ROM (from a Plus/4). Click for larger view.

Project - Switch PAL C-116 to NTSC and upgrade the RAM to 64K. These two changes will create a mini Plus/4. Together with a uIEC cart for storage and a mini-flatpanel screen from a portable CD player I will have a nice portable Commodore system that I can travel with on an airplane, etc.

From cbm-hackers:

- Replace the 2 RAMs with 41464 (64Kx4) DRAM
- Cut trace between pin 14 and Pin 16 of U8 (topside)
- Cut trace between pin 16 and Pin 2 of U7 (underside)
- Make a new connection between CPU Pin 22 and U7 Pin 2
- Make a new connection between CPU Pin 21 and U8 Pin 14

"..Now you should be greeted with 60671 Bytes free..."

U7 and U8 are the two 74LS257.

Probably I will also upgrade the 7805 V regulator as I expect more heat to be generated.

[41464 (64Kx4) DRAM ordered. $9.00 new on Ebay for 5.]

I have done this before, find an NTSC system that is not working and swap into the target system. I need:
14.31818 MHz Crystal
NTSC Plus/4 Kernal ROM (318005-05)

I can do this while I wait for the RAM to be shipped.

THe uIEC does not fit in the C116 cartridge port, but that's OK because I want to be able to use the C-116's cartridge port for an assembler/monitor cart I have. To power the uIEC I plan to hot-wire the +5V pin on the cassette DIN port.

Commodore C-116 Computer SN label
View of the underside label with serial number. Note "264 Series" on the label. This was dropped with the later Plus/4 model.


  C-116 PAL to NTSC Conversion by Bill Degnan - 08/27/2013 13:28
Commodore C-116 NTSC Motherboard
View of the oscillation crystal for NTSC display installed in the C-116 motherboard. Interestingly the motherboard has drill holes for both PAL and NTSC crystals, accommodating for a future NTSC version of the C-116 that never materialized. I borrowed a 14.31818 MHz crystal from spare C-64 parts that fits perfectly. Click image for a view of the entire "NTSC" motherboard including a Plus/4 NTSC Kernal ROM 318005-05

Commodore C-116 NTSC Boot Screen
Commodore C-116 boot screen after successful NTSC conversion. The dark horizontal scan line across the screen is an artifact of the camera, not actually present on the display. Note 12227 bytes free.

  C-116 RAM 64K RAM Upgrade by Bill Degnan - 08/28/2013 11:53
Commodore C-116 Motherboard
First I removed the old RAM and replaced with two 414S4C-10 RAM chips = 64K. Not pictured, I also cut the trace between pin 14 and Pin 16 of U8. Click image for larger and expanded view of motherboard.

Commodore C-116 64K mod motherboard underside
A closeup of jumpers added to the underside of the motherboard which are necessary for the 8501 CPU and the two 74LS257's (U7 and U8) to use all 64K RAM. If you leave off the black wire connecting U8 to pin 21 of the 8501, the system will still report the full RAM, but then bombs when more than 16K RAM is needed such as when loading a program from disk. After this pic was taken I cleaned up the solder. The arrow in the picture points to the cut trace between pin 14 and 16 of U8. Click image for full underside view of the C-116 motherboard with 64K Mod jumpers.

NTSC CBM C116 with 64K
And we're done. A 64K NTSC C-116.

With all this hacking looks like I blew out the TED chip's (8360) keyboard latch, causing the joystick to not respond correctly (i.e. game character does not go up in response to joystick movement). Need to replace from donor system. Thanks to CROCK of vintage-computer forums for diagnostic details how/to. Here is a link to his site:

  TED Chip Replacement by Bill Degnan - 08/29/2013 19:11
Replaced the TED chip which I apparently blew out, or was never good to begin with when I got the C-116...either way, project complete!

  Schematic by Bill Degnan - 09/06/2013 23:44
Bil Herd posted schematics that I can use to mess around with the board. I found that the TED chip was good after all, I guess it overheated, but not permanent damage. Worked later on.

I picked up a teeny fan that uses 3.6v, and I may add this fan to blow over the TED. I already added heatsink paste to the TED chip where it attaches to the metal heat shield.

  Screen Shots by Bill Degnan - 09/10/2013 14:02
Plus/4 Ted ACE screenshot
C-116 after mods, running Plus/4 game called ACE, a fighter simulation. Click image for larger view.

Plus/4 disk directory
Disk directory. Note file sizes are larger than what a normal C-116 or C-16 could handle. Click image for larger view.

Plus/4 Trailblazer game screenshot
Pretty sure this is Trailblazer game. Click image for larger view.

Plus/4 Escape screenshot
Escape maze game. Click image for larger view.

Plus/4 Frogger Screenshot
A Frogger clone. Click image for larger view.

Plus/4 Tutti Frutti game screenshot
Tutti Frutti game splash screen. Click image for larger view.

  JiffyDOS for 264 Installed by Bill Degnan - 10/03/2013 14:01
Commodore JiffyDOS for Plus/4 and other 264 /TED machines
Boot screen after the installation of the a TED/264 version of the JiffyDOS Kernal ROM, version 6.01. Click image for larger view.

What's Next? I'd love to find a RR-Net type device to connect the C-116 (or Plus/4) to an Ethernet port, for IRC chat or telnet.



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