TRS-80 Model II
 | |
| TRS-80 Model II display console and keyboard (Piergiovanna Grossi, CC BY-SA 4.0) | |
| Specifications | |
|---|---|
| Manufacturer | Tandy Corporation, sold through Radio Shack |
| Type | Business computer |
| Released | 1979 |
| Discontinued | 1983 |
| Intro price | US$3,450 (32 KB); US$3,899 (64 KB) |
| CPU | Zilog Z80A at 4 MHz |
| Memory | 32 KB or 64 KB |
| Storage | One 8-inch floppy drive (Shugart SA800); up to three more in the Disk Expansion Unit |
| Display | Built-in 12-inch monochrome CRT; 80 or 40 characters by 24 lines |
| Sound | — |
| Ports / interface | Two RS-232-C serial, one parallel, disk expansion |
| Power | 150 W switching power supply (AA11080) |
| OS / Firmware | TRSDOS |
| Successor | TRS-80 Model 12 |
| Model no. | 26-4001 (32 KB), 26-4002 (64 KB) |
The TRS-80 Model II is a Z80-based business computer that Tandy Corporation sold through Radio Shack from 1979. It was introduced at the National Computer Conference in New York in June 1979, and Radio Shack shipped 1,000 by the end of that year.[1] The display console holds the screen, an 8-inch floppy drive, the power supply and a card cage of plug-in boards; the keyboard is a separate unit on a cable.[2] It is a different design from the TRS-80 Model I and, apart from simple BASIC programs, does not run Model I software.[1]
Guides: TRS-80 Model II General Maintenance, TRS-80 Model II Troubleshooting Guide and TRS-80 Model II Capacitor Replacement Guide.
History
[edit | edit source]The 32 KB Model II (catalogue number 26-4001) cost $3,450 and the 64 KB model (26-4002) $3,899; a 32 KB machine could be upgraded with the 32K Add-On (26-4102). Radio Shack began taking orders in June 1979 for delivery in October. Ira Goldklang's TRS-80 site gives May 1979 for the announcement.[1][3] Radio Shack sold it alongside the Model I as a separate line for larger jobs, and would not take Model I trade-ins.[1]
In January 1982 Radio Shack introduced the Model 16, which runs Model II software and adds a Motorola 68000; a Model II could be converted with the Model II to Model 16 Upgrade Kit (26-6010). The Model II was discontinued in 1983, after its replacement, the Model 12, was introduced.[1]
Specifications
[edit | edit source]| Item | Detail |
|---|---|
| CPU | Zilog Z80A at 4 MHz, on the CPU card with the bootstrap ROM, DMA controller and dual serial interface |
| Memory | 32 KB or 64 KB of 16K dynamic RAMs on the memory card |
| Display | 12-inch CRT monitor; 80- or 40-character lines, 24 lines; upper and lower case, forms-drawing characters and reverse video; MC6845 CRT controller on the video card |
| Storage | One 8-inch floppy drive, single and double density, 77 tracks |
| Keyboard | Separate 76-key capacitive keyboard with an 8021 microcontroller, sending serial data to the video/keyboard card |
| Interfaces | Two RS-232-C channels, a parallel printer port and a connector for the Disk Expansion Unit |
| Expansion | Motherboard with eight 80-pin card-edge slots, four used by the standard boards |
| Power supply | 150 W open-frame switching supply: +5 V at 8.6 A, +12 V at 4.5 A, +24 V at 1.7 A, −12 V at 0.2 A; jumper-selected for 95-135 V AC or 190-270 V AC, 50 or 60 Hz |
Source: Technical Reference Manual, pp. 3-4, 127 and 135.[2]
Hardware
[edit | edit source]Display console
[edit | edit source]The display console is built from ten subassemblies: case, chassis, power supply, card cage, CPU card, floppy disk controller (FDC) card, memory card, video card, video monitor and floppy drive.[2] The card cage's motherboard has eight 80-pin card-edge connectors. As shipped, the cards sit in this order, slot 1 being nearest the power supply:[2]
| Slot or position | Subassembly | Manufacturer's part no. | Radio Shack part no. |
|---|---|---|---|
| Slot 1 | CPU board | 8893405 | AXX0501 |
| Slot 2 | FDC board | 8893425 | AXX0505 |
| Slot 3 | Memory board, 32K or 64K | 8893410 (32K), 8893415 (64K) | AXX0502, AXX0503 |
| Slot 4 | Video generator board | 8893420 | AXX0504 |
| Card cage | Motherboard assembly | 8893430 | AXX0500 |
| Chassis | Power supply, AA11080 | 8790010 | AXX6003 |
| Chassis | CRT with video board | 8709043 | AXX8000 |
| Chassis | Disk drive, SA800 | 8709042 | AXX5002 |
| Keyboard | Keyboard module | 8790504 | AXX0204 |
A 32K add-on memory board, where fitted, goes in slot 5.[2]
Power supply
[edit | edit source]The AA11080 is a 150 W open-frame switching supply. It rectifies the mains, chops it at 20 kHz, and transforms and rectifies the result into four isolated outputs, with feedback loops for regulation and over-current protection. It must always have a load connected: run without one, it can break into damaging oscillation.[2] Radio Shack's own service text calls it the "Astec power supply".[4] Its schematic, test procedure and specifications are in section IX of the manual; see TRS-80 Model II Troubleshooting Guide.
Video monitor
[edit | edit source]The 12-inch monitor takes video, horizontal drive and vertical drive from the video card and +12 V from the power supply. Radio Shack documented two versions, the Motorola M3970-series board and an RCA board (VDC-1), and the manual has a separate parts list and schematic for each.[2] The CRT and its video board are a matched set and are replaced together.[2] Owners have used the manual to identify RCA boards in surviving machines.[5]
Floppy drive
[edit | edit source]The internal drive is an 8-inch Shugart SA800 with two motors, one turning the disk and one positioning the head over 77 tracks. Machines built for export could have an AC drive motor for the local mains voltage and a different pulley for 50 Hz. Without a Disk Expansion Unit attached, the manual requires a terminator board on the disk expansion connector at the back of the console.[2]
Keyboard
[edit | edit source]The keyboard is a 76-key low-profile capacitive design. An 8021 microcontroller scans the matrix and sends each key code serially to the keyboard interface on the video card.[2]
Start-up and diagnostics
[edit | edit source]At switch-on the bootstrap ROM sets up the CRT controller (giving a white screen), checks its own checksum, tests the Z80 and tests the RAM from 1000H to 7FFFH, then shows INSERT DISKETTE. A failure stops it with a two-letter error such as CK, Z8 or MF; disk faults give DC, D0, SC, TK, LD or RS. The full list is on TRS-80 Model II Troubleshooting Guide.[2] Radio Shack sold a diagnostic diskette, part number AXX2012, for deeper testing.[2]
Known faults
[edit | edit source]- Owners report low or missing rails from old AA11080 supplies: no +5 V and +24 V reading 27.8 V on one machine, +5 V at 4.6 V on another.[6][7] Some have replaced the AA11080 with a modern four-output supply, reusing the original output connector.[8]
- The 80-finger card edges and the chip sockets oxidise; owners clean the card edges with a soft pencil eraser[7] and treat the sockets with contact cleaner.[6] On one memory board the RAM chips' silver-coloured legs had turned black and some had broken off.[6]
- Keyboards stop registering keys as their pads age, and the keyboard cable frays at its connector.[6]
See TRS-80 Model II Troubleshooting Guide for diagnosis.
Documentation
[edit | edit source]- Radio Shack TRS-80 Model II Technical Reference Manual: catalogue number 26-4921 (1980). Theory of operation, troubleshooting to board level, disassembly, the AA11080 power supply procedures and a parts list and schematic for every board, both monitors and the keyboard.
- The Model II community archive at github.com/pski/model2archive holds board schematics, Radio Shack customer service bulletins and the Tandy diagnostic disks.[9]
Related pages
[edit | edit source]- TRS-80 Model II General Maintenance
- TRS-80 Model II Troubleshooting Guide
- TRS-80 Model II Capacitor Replacement Guide
- Tandy TRS 80 (Model I)
- TRS-80 Model III
- CRT Discharge Procedure
- Floppy Drive Repair
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 Matthew Reed, "The TRS-80 Model II", TRS-80.org (retrieved 2026-10-21). Introduction at the June 1979 National Computer Conference, first deliveries in October 1979, catalogue numbers and prices, specifications, the Model 16 upgrade kit and the Model 12.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 Radio Shack, TRS-80 Model II Technical Reference Manual, catalogue number 26-4921, 1980. Hosted here as File:Radio Shack TRS-80 Model II Technical Reference Manual (26-4921, 1980).pdf (see Radio Shack TRS-80 Model II Technical Reference Manual). Page numbers on this page are the manual's printed page numbers.
- ↑ Ira Goldklang, "TRS-80 Model II: Specs, Pricing and Options", TRS-80 Revived (retrieved 2026-10-21). Specifications and Radio Shack catalogue entries for options and peripherals. Community source.
- ↑ Technical Reference Manual, p. 91, "Service Notes": precautions before working on the video monitor, including discharging the two large high-voltage capacitors on the Astec power supply.
- ↑ VCF Forums, "TRS-80 Model 2 - first startup after recapping but CRT shows only disappearing horizontal line", September 2024 (retrieved 2026-10-21). The owner identifies the RCA monitor board from the Technical Reference Manual. Community source.
- ↑ 6.0 6.1 6.2 6.3 VCF Forums, "TRS-80 Model II repair log", May-September 2024 (retrieved 2026-10-21). Missing +5 V, cleaning, corroded RAM legs, monitor recap, keyboard pads and cable, diagnostic ROM. Community source.
- ↑ 7.0 7.1 VCF Forums, "Model II boot error RS next steps", July 2020 (retrieved 2026-10-21). Low +5 V, cleaning the card edges with a soft pencil eraser, reseating cards, the reset switch, the meaning of BOOT ERROR RS. Community source.
- ↑ VCF Forums, "Model II power supply advice", May-June 2015 (retrieved 2026-10-21). Replacing the AA11080 with a four-output supply and reusing the original output connector. Community source.
- ↑ pski and contributors, "model2archive", GitHub repository (retrieved 2026-10-21): Documents (customer service bulletins), Hardware (Model II, 12, 16 and 16B schematics and service manuals), Software/Diagnostics. Community archive.