Tandy TRS-80 Model 100 Teardown

In 1983, Tandy released the TRS-80 Model 100 at $999 (US). Adjusted for inflation, the machine would cost $2,187 (US) in 2010.

The Model 100 came with an 2.4MHz 8-bit Intel 80C85 CPU (a CMOS verions of the Intel 8085) and 8Kb of base RAM (expandable to 32KB). The machine aslo came with an onboard ROM, which stored pre-installed software, such Basic, Text, Telcom, and Schedule, and Address.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The Tandy TRS-80 Model 100 measured 11.8 inches wide by 8.5 inches tall by 2 inches thick. It weighed just over 3 lbs. (with four AA batteries).

Photo by: Bill Detwiler
Caption by: Bill Detwiler

When we originally purchased this unit, it still had the batter compartment cover. But, it's gone missing in the last two years.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

This TRS-80 Model 100 was manufactured in Japan by Kyocera for Tandy/Radio Shack.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The TRS-80 Model 100 used four AA batteries.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The Model 100 has a Memory Power switch. If the 4 AA batteries ever go dead or are removed, the switch let's you use the CMOS battery to power the memory and store data.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Along the Model 100's right side are the power switch, display contrast wheel, and DC power connector.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Along the Model 100's left side are the port for an external bar code reader and two switched for the internal 300-bps modem.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Along the top edge of the Model 100 are a reset button, 25-pin RS-232C serial port, Centronics printer port, internal modem port (labed Phone), and port for an external cassette tape drive.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

This photo shows the Tandy TRS-80 Model 100 next to a 2010 MacBook Pro. It's interesting to see how much thinner today's machines are.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

You could add programs to the TRS-80 Model 100 through preprogrammed ROMs, which could be installed here.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Unlike many of today's portable computers which use special tamper-resistant screws, the TRS-80 Model 100 uses standard Phillips screws. There are four external screws that need to be removed.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

With the four external screws removed, you can lifting the top half of the case away from the bottom. There are several cables that connect the two halves, so lift up from the machine's left side (where the bar code reader port is).

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Luckily, the internal cables on the TRS-80 Model 100 are long enough to lay both halves next to each other.

The motherboard and ports remain in the lower half of the case, while the display, keyboard, and internal speaker are attached to the top.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

You'll need to disconnect the cables for the display, speaker, and keyboard before separating the two halves of the TRS-80 Model 100.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The display, keyboard, and speaker are attached to the top half of the the TRS-80 Model 100's case.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The motherboard and ports are attached to the lower half of the TRS-80 Model 100's case. We'll take a more detailed look at the motherboard and its attached components in a minute, but for now, let's turn our attention back to the upper half of the case.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Five Phillips screws hold the TRS-80 Model 100's keyboard in place.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The TRS-80 Model 100's keyboard had 56 keys, eight programmable function keys, four dedicated command keys, and four arrow keys.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The TRS-80 Model 100's internal speaker is connected to the display's PCB with a thin wire. You'll need to disconnect this wire before removing the display assembly.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Four Phillips screws hold the TRS-80 Model 100's LCD display assembly to the upper half of the case.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

With the screws removed, you can lift the Model 100's display screen and PCB away from the case.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The TRS-80 Model 100's monochrome LCD display provides a resolution of 240 x 64 pixels and can show eight lines of text. The screen was not backlit.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

There are several large Hitachi HD44102 Dot Matrix Liquid Crystal Graphic Display Column Driver chips mounted to the back of the display's PCB.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Along with the HD44102 chips, there are two Hitachi HD44103 Dot Matrix Liquid Crystal Graphic Display Common Driver chips mounted to the display's PCB.

According to documentation on Alldatasheet.com, the smaller HD44103 chips generate the timing signals required for display with their internal oscillator and supply them to the HD44102 column driver to control the display.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

A single Hitachi HA17902 Quad Operational Amplifier is also mounted on the display's PCB.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The TRS-80 Model 100's internal speaker is held to the frame with clear, plastic screws. I used a #00 Phillips screw driver bit to remove them.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Photo by: Bill Detwiler
Caption by: Bill Detwiler

With the upper case completely disassembled, let's turn out attention back to the lower half of the TRS-80 Model 100.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The first step in removing the TRS-80 Model 100's motherboard from the lower half of the case is to disconnect the green ground wire.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

After disconneting the ground wire, you can lift the power connecter away from its slot in the case. You do not need to disconnect its wires from the motherboard.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Although it's not necessary to remove the plastic bar that covers the serial and printer ports, I went ahead and did so.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The motherboard is held to the lower half of the case with seven Phillips screws.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

With the screws removed, you can lift the TRS-80 Model 100's motherboard away from the lower half of the case.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

There's nothing left in the case but a thin metal shield and attached ground wire.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

There's lots to see on the top of the TRS-80 Model 100's motherboard.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The main points of interest in this corner of the motherboard are the OKI MSM80C85ARS processor (upper left), D3-6402-9 UART chip (upper right), and Toshiba TC5518BF-25 RAM (lower right).

Photo by: Bill Detwiler
Caption by: Bill Detwiler

This Model 100's Intel 2.4MHz 80C85 CPU was manufactured by OKI and has markings MSM80C85ARS.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Toshiba TC5518BF-25 RAM

This unit has 8Kb of RAM.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

This D3-6402-9 UART chip drives the TRS-80 Model 100's RS232 serial port.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

This MC81C85RS I/O controller chip drives the keyboard, parallel printer, speaker, clock, and LCD.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Below the serial connector and I/O controller chips and to the right of the RAM chip, there are solder points for the option ROM sockets, which are mounted on the underside of the motherboard.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

This Sharp LH535618 ROM chip contains the TRS-80 Model 100's built-in software, such as BASIC.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

There are many different Toshiba TC40H chips mounted around the motherboard, which are used for the keyboard.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

As noted eariier, this 3.6V rechargeable battery would power the information stored in memory if the four AA batteries were removed or went dead.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The motherboard on this TRS-80 Model 100 has the marking PLX100CH1X.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

The underside of the TRS-80 Model 100's motherboard doesn't have any real points of interest except the Memory Power switch and sockets for the option ROMs.

Photo by: Bill Detwiler
Caption by: Bill Detwiler

Thanks to TRS-80 Model 100's standard Phillips screws and sturdy construction, cracking it open was an simple and enjoyable process. It's also interesting to see how the internal components of notebook computers have change in 28 years.

You can find out more about the Tandy TRS-80 Model 100 with the following links:

• Model 100 Technical Reference Manual
• Tandy Model 100 Service Manual

Photo by: Bill Detwiler
Caption by: Bill Detwiler