TRS-80 Model I Hardware Parts and Repairs

Using a Composite Monitor In Lieu of a Model I Monitor

Model I Composite Cable

The TRS-80 was originally sold with a 13" RCA Black and White Television with most of the guts ripped out. However, there can be times that a monitor is not available, you can build this cable to connect your Model I to a composite monitor. For instructions, visit here.

From time to time, Tuc's Workbench has them for Sale as well.

Cases

Model I Case

Dusty's Vintage Workship makes replacement Model I Keyboard cases for original hardware. They are 3-D printed using PLA+ construction.

You can find those at https://dustysvintageworkshop.com/products/model-1-case.html.

Model I Bezel

Dusty's Vintage Workship makes replacement Model I Keyboard bezels for original hardware. They are 3-D printed using PLA+ construction and come with a raised resin badge.

Expansion Interface

Expansion Interface Case

If you have an Expansion Interface but no case, Andrew Quinn has created this perspex "case", which he advises is strong enough to support the monitor.

Drilling instructions can be found here.

ROM

Dusty's Vintage Workshop

Dusty's Vintage Workshop sells a single modern ROM containing the last known stable version of Level II BASIC 1.3. They write

Many Model I computers have accumulated factory daughter boards, ROM modifications, and repair work over the years. This upgrade simplifies the ROM configuration.
  1. Contains Level II BASIC version 1.3
  2. Removes factory daughter boards and ROM hacks
  3. Helps improve Model I stability
  4. Returns the system to a cleaner, easier-to-service configuration

You can find more information at https://dustysvintageworkshop.com/products/level-ii-rom.html.

Tuc's Workbench

Tuc's Workbench is now selling a USB programmable ROM replacement. They write

The most flexible ROM replacement for your retro computer. It is highly configurable and low-cost. Get them fabbed at JLC for under $5 each in a quantity of 10 or more.

Based on a Raspberry Pi RP2350 (One ROM Fire 🔥) or STM32F4 (One ROM Ice ❄️).

One ROM is available as 24 pin and 28 pin versions, emulating nearly all systems' 24 and 28 pin ROMs, including any possible chip select configurations, and can serve different images to multiple ROM sockets simultaneously.

Replaces failed ROMs in Tandy, Commodore 64s, VIC-20s, PETs, Ataris, BBC, TIs, disk drives and many other types of systems.

ROM types replaced:

24 pin: 2704, 2708, 2716, 2732, 2316, 2332, 2364

28 pin: 2764, 27128, 27256, 27512, 23128, 23256, 23512

One ROM was formerly known as Software Defined Retro ROM (SDRR).

Key Features:
  • Based on sub-$2 microcontrollers. Choose from Raspberry Pi (Fire) or STM (Ice)
  • Fast enough for Tandy, PETs, VIC-20s, C64s, 1541s, IEEE drives, etc. Support faster systems with higher end microcontroller.
  • Same footprint as original ROMs - doesn't overhang the socket like other solutions.
  • USB version - no programmer required, program from your browser.
  • Quick Programming- build and flash in <10 seconds.
  • eflash in situ- no need to remove the ROM from the host when reprogramming.
  • Software configurable chip select lines - no hardware jumpers required.
  • Stores up to 16 rom images of different sizes and chip select configurations. Image selectable via jumpers.
  • Replace multiple roms with one a single One ROM can replace up to 3 original ROMs e.g. all of C64 kernel, BASIC, character set.
  • Dynamic Bank Switching - switch between ROM images on the fly, e.g. different char ROMs.
  • Hackable at runtime - change the ROM images being served and access telemetry from the ROM at runtime using AirFrog or other SWD probes.
  • Images combined automatically - no need to manually build up your own larger PROM image containing multiple retro ROMs.
  • Two layer PBC - component on single-side, limited BOM for low manufacturing cost/complexity
  • Open Source software and hardware

You can find the page at https://shop.tucs-workbench.com/products/one-rom-one-rom-to-rule-them-all.

Building a Replacement Model I Power Supply

It is very common today for people to have Model I power supply issues. While common wisdom says to cut open non-working supplies and check/replace the fuse, sometimes that is not possible, that is not the problem, or the individual is missing a supply altogether.

Buy One

Dusty's Vintage Workshop sells two different versions of compact, lightweight, modern replacement Model I Power Supplies.

  1. Single - Single power supply can be found at at https://dustysvintageworkshop.com/products/compact-power-supply.html.
  2. Dual - A power supply that supply both the Model I CPU and Expansion Interface can be found at https://dustysvintageworkshop.com/products/dual-power-supply.html

Make One

Three individuals have prepared schematics and instructions on building a replacement power supply using current-day easy-to-find parts.

  1. Charles - For instructions, download this PDF. Note: This design has parts which are easier to procure within the USA.
  2. Marcel Erz - For instructions, visit here.
  3. Dusty's Vintage Workshop - For a video constructing one, visit here.