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2 x Commodore Amiga 600 Full Recap and Repair

April 10th, 2016 No comments

2 x Commodore Amiga 600 Full Recap and Repair.

Commodore Amiga 600 #1:

  • Full SMD Capacitors Recap.
  • Replaced the joystick port with a missing two pins. The joystick port has been recovered from a pcb (not amiga) for spare parts.

Gallery:

Commodore Amiga 600 #2:

  • Full SMD Capacitors Recap.

Gallery:

TRS-80 Model 1 L2 – Video Snow Shovel Hardware Fix

April 10th, 2016 2 comments
TRS-80 Model 1 L2 - Video Snow Shovel Hardware Fix

TRS-80 Model 1 L2 – Video Snow Shovel Hardware Fix

Video snow, the black streaks against white characters, is most apparent with large, rapidly changing areas of white graphics. The root of the problem is that the TRS-80 display is memory mapped by the CPU.

The solution is to give the video circuitry higher priority than the cpu.

Note:

On my TRS-80 Model 1 where i use the Quinnterface & FreHD i had to use the version that also includes the 74LS125 which seemed optional but in this case it does not appear to be optional, we have to do it, otherwise doesn’t work.

Thanks to Ian Mavric for the support.

Gallery of the hardware mod:

Download: 80 Microcomputing Magazine 1982 (790)

TRS-80 Model 1 L2 – Lowercase characters Hardware mod

April 10th, 2016 1 comment
TRS-80 Model 1 L2  - Lowercase characters Hardware mod

One of the most famous limitations of the TRS-80 Model I was its inability to display lower case characters.

Although the lower case characters were present in the character set, the Model I lacked the extra memory chip needed to store the bit corresponding to lower case.

The significance of this limitation has been exaggerated over time (it is worth noting that at that same time the Apple II also lacked lower case), but it created a real problem for word processors. Many lower case upgrades for the Model I were created to address the omission, ranging from simple to more complex.

The TRS-80 video display uses a dedicated block of 1024 bytes of memory located in memory space at 3C00 Hex. When received from the factory, there are only 7 memory chips installed in this block of memory, providing 128 possible characters for screen display. The stock TRS-80 uses 64 of these combinations for graphics and a second 64 for the upper-case subset of the ASCII character set. Bits 0-5 control the character selection, and the highest bit (bit 7) is used to determine if the character is alpha-numeric or graphic. Bit 6 is missing!

To add lower-case display, bit 6 must be implemented. This may be accomplished by switching the memory chip for bit 7 to bit 6, thereby enabling lower-case letters and eliminating graphics, or by addition of an 8th memory chip. We prefer adding the extra chip. In either case, if you plan to use Level II BASIC, you must include a switch to disable bit 6, or BASIC will place a lot of funny characters on the screen!

Gallery of the hardware mod:

Download: Lowercase characters Hardware mod (999)

source: trs-80.org

TRS-80 Model 1 L2 – Assembling Quinnterface & FreHD Interface

April 10th, 2016 No comments
TRS-80 Model 1 L2 - Assembling Quinnterface & FreHD Interface

TRS-80 Interfaces in KIT from Ian Mavric and J. Andrew Quinn.

I begin to assemble the kit:

  • “Quinnterface” is a Mini Expansion Interface for TRS-80 Model I with 16K. Neat little device is perfect for Model I users who own a 16K Level II unit (which is most of you) but no EI or Disk Drives, and don’t want to modify your Model I with upgraded boot Rom or memory upgrade. The Quinnterface, developed by J. Andrew Quinn from New Zealand, adds 32K RAM and auto-boot functionality to your FreHD.
  • “FreHD” SD Card HARD DRIVE Emulator for TRS-80 Model I/III/4.

The complete kit consists:

  • Quinnterface.
  • FreHD.
  • Model 1 Hard Drive Adapter.
  • BoHx. A small neat enclosure for your FreHD!
  • CD ROM / Stickers and Cables.

Gallery:

source: ianmav.customer.netspace.net.au/trs80/