Color Computer 2

Color computer 2

Models

The CoCo2 was first released in September of 1983.

• CB = Color Basic
• ECB = Extended Color Basic

26-3026, 26-3026A, 26-3026B model (16K CB ) - September 1983

The first CoCo 2 model released included 16K RAM with standard Color BASIC and was listed in Radio Shack catalogs at U$239.95. The case was a bit smaller than the original CoCo, very similar to the TDP-100. The keyboard was much better than the original CoCo "chicklet" keyboard. They were lower profile than typical modern PC keyboards and the keys were recessed in the center, giving them a "melted" look - a term now used to describe this model.

The circuit boards were revised to be a bit smaller than previous models and were equipped to run a full 64K. Most of its chips are socketed. This machine is based on the #8709416 PC board, and has a large, upright RF modulator with integrated TV channel 3/4 switch.

Also characteristic of this machine is the use of a large power supply pass transistor (in a TO-3 package). The two 24-pin ROM sockets are located near the cartridge/system bus connector, and the eight RAM chips are located in a single row under the keyboard.

This same model number has reportedly been found on larger, Korean-made CoCo models in Australia.

There are two possible versions (and 'A' and 'B') for this catalog number.

26-3027 (16K ECB), 26-3003 (64K ECB)

This 16K ECB model was listed for $319.95, $399.95 for 64K. A 64K RAM upgrade (26-3017/26-3017B) was "only" $149, and the Extended BASIC ROM upgrade (26-3018) was $79.95, making the $399.95 26-3003 a relative bargain (add the ROM and RAM upgrade to a 16K basic model the total price was $468.90).

The 26-3027 model is identical to the 26-3026, with the exception that it already has the Extended BASIC ROM factory-installed.

There are two possible versions (and 'A' and 'B') for the 26-3027 catalog number.

RAM upgrade

To upgrade the 26-3026 or 26-3027 to 64 KB of RAM, it is necessary to replace the eight 8040517 chips with 4164 chips of 200 ns or better access time, and to solder a wire between the two pads labelled W1. W1 is located between U6 and U7.

Example documented upgrades :

• 26-3026 model 16K to 64K upgrade

26-3126 (64K, ECB) CoCo 2 kit

This particular model was sold as the "Color Computer 2 Kit" in the educational market as a kit of parts to be assembled. It included a booklet with full instructions to assemble the kit into a full CoCo 2 system, including the board and all electronics parts but also power supply, keyboard and complete white plastic case.

• https://www.facebook.com/groups/2359462640/posts/10153646511017641/
• https://www.facebook.com/groups/2359462640/posts/10159470040357641/

26-3127 (64K, ECB), 26-3127B

This is the first '64K Color Computer 2'. It also featured the 'enhanced' keyboard, otherwise, it is identical to the 26-3026/26-3027.

RAM replacement

Note that the RAM is soldered in place in those machines which were factory-equipped with 64K, making replacement thereof a bit more difficult if necessary. For this reason, the 26-3026 and 26-3027 variants are favorites among CoCo 2 enthusiasts.

The Korean-made CoCo 2s

26-3134 (16K CB), 26-3136 (16K ECB)

The 26-3134 model is the first Korean-made 16K Color BASIC CoCo 2. It uses the #20261043 circuit board, which differs considerably from that used in the earlier USA-made models. Virtually every component on the board has been relocated. The RF modulator is now a smaller unit, lying flat on the board rather than standing upright, and the channel 3/4 switch has been moved to the main board from the modulator. The positions of the various switches and connectors on the PC board (and therefore on the rear panel) differ from those of the previous machines as well. The RAM chips are located in two rows (one of five and one of three chips).

This machine has a metal 'cage' surrounding the power transformer, which was not present in previous models. The power supply utilizes a cooler-running pass transistor (in a TO-220 package). The RF modulator, power transformer, pass transistor, and switch/jack location characteristics of this machine persist on all subsequent models. Most chips are soldered in place on this and all subsequent boards as well.

The 26-3136 model is identical to the 26-3134, but with the Extended BASIC ROM factory-installed.

26-3134A (16K CB 1.3), 26-3136A (16K ECB)

The 26-3134A model is the next Korean 16K Color BASIC CoCo 2. It utilizes a #20261044 circuit board, which differs considerably from the previous versions.

The 26-3136A model is the 16K Extended BASIC version of the 26-3134A.

ROM upgrade

The 26-3134A and 26-3136A models use boards with 28-pin, 16-kilobyte ROMs containing both Color BASIC and Extended BASIC.

28 pin EPROMs are commonly available. When flashing them, the ECB ROM file should be concatenated to the Color BASIC ROM resulting in one single file to be flashed. See EPROM Programming for an example.

26-3134B (16K CB 1.3), 26-3136B (16K ECB)

The 26-3134B model is the last Korean 16K Color BASIC model. It uses the #20261058 circuit board, which is similar to the #20261044 board. It uses two 4416 RAM chips and a 24-pin Color BASIC 1.3 ROM in a 28-pin socket as well. However, in addition to the 4416/4464 sockets and special daughter board connectors, there are pads on the board allowing direct factory installation of eight 4164 chips. This is also the board which contains the newer 6847T1 VDG chip (which is not pin-compatible with the earlier 6847).

The 26-3136B model is the Extended BASIC version of the 26-3134B.

26-3127B (64K ECB ) (some with lowercase support)

The last Korean-made model number associated with the 64K ECB CoCo 2, this is an odd one indeed.

Some of the 26-3127B CoCo 2 models are known to have been produced with different Video Display Generator (VDG) chips, either the Motorola MC6847 or the enhanced MC6847T1 (marked XC80652P, spec sheet). In comparison, the CoCo3 does not have a real 6847; it has a custom chip (the ACVC) with an internal character generator ROM.

Among these models we find :

• A USA-made TRS-80 with a #20261044 board and a 6847
• A USA-made Tandy with a #20261058 board and a 6847T1
• A Korean-made Tandy with a #20261058 board and a 6847T1.

They were three distinctly different machines, each bearing this same exact 26-3127B model number. This VDG chip is also known as the 6847 or 6847T1, the T1 version would include a lowercase character set.

Contrary to some rumors, the presence of the 'B' in the model number does NOT necessarily indicate the presence of a 6847T1. As noted previously, the Tandy label appears to be the best external indication thereof.

One absolutely accurate method of determining if one is present is to type a '0' (zero) on an operating machine. If the resulting character on the screen is displayed with a slash through it, the machine in question has a 6847T1.

• Tandy Coco 2B true lowercase fonts
• 6847t1 Font Mystery
• Typography in bits: For a few pixels more
• Korean-Made CoCo 2 Identification (either 6847 or 6847T1)

RAM upgrades for Korean models

These 64K RAM upgrade notes apply to 26-3134A, 26-3136A, 26-3134B, or 26-3136B models ONLY.

The board's RAM is in the form of two socketed 4416 chips. The preferred 64K upgrade these models involves replacing them with two 4464 chips of 200 ns or better access time and to solder a jumper across the two pads labeled RAM SIZE 64K. The RAM SIZE 64K jumper is located next to IC4.

For the 26-3134A model the option also exists (by means of several special connectors on the board) of a factory upgrade consisting of eight 4164 chips on a daughter board. Legend has it that the option of using either 4164s or 4464s was incorporated for economic reasons (the pricing and availability of RAM were quite unstable when these machines were manufactured). Additionally, this board introduces the use of a single 28-pin ROM socket. A 24-pin ROM containing only Color BASIC 1.3 shipped in that socket in this model. With appropriate jumpering, this socket is able to accept a 27128 EPROM.

Pricing

Prices dropped quickly. In mid 1984 RS cut the price for the 16K standard model to $159.95 and the 16K Extended BASIC model to $199.95. Production then shifted from Tandy's US plant to a Korean subcontractor. Those models appeared in mid 1984 at the same prices as the previous models, with new model numbers and revised circuit boards. For Christmas 1984 prices were reduced -- $99.95 for a standard Color BASIC 16K model (31-3134), $139.95 for 16K and Extended Color BASIC (31-3136), and $199.95 with 64K and Extended Color BASIC (31-3127). Prices continued to drop as the home computer market got very competitive and IBM PC clones started coming down in price.

To put these prices in perspective, the new for 1985 Tandy 1000, which was an IBM PC clone (actually an enhanced IBM PC Jr. clone that could be upgraded to standard IBM PC specs) was listed at $1,199 with 128K RAM and a single 360K floppy drive. An RF modulator could be purchased ($24.95) to use a standard TV as a display (limited to 40 columns) or a digital $159.95 monochrome/$549.95 color monitor could be used. The CoCo 2 was a relative bargain, although there were a few IBM clones that could be purchased a bit cheaper than the Tandy 1000. In 1987 the Tandy 1000SX was priced at $849 with 384K of RAM and one 360K floppy drive.

The final CoCo2 was listed in the 1987 Tandy catalog for only $99.95 with 64K and Extended Color BASIC.

Differences

Extracted from The CoCo 2, introduced in 1983, is basically a refinement of Radio Shack's original TRS-80 Color Computer. It utilizes a more efficient power supply, higher integration (lower parts count), and a smaller case. The primary goal of these modifications was most likely to lower its manufacturing cost. The only significant functional difference between the two is the absence in the CoCo 2 of a regulated +12VDC power supply. One of the few devices which actually requires this power source is the first-generation floppy disk controller sold for the original CoCo. All subsequent controllers operate exclusively from the +5VDC line. The CoCo 2 was initially offered with 16 kilobytes of RAM, with the option of upgrading it to 64 kilobytes. Doing so requires considerably less effort than in previous models (typically replacing the RAM chips and soldering one jumper).

While the original CoCo used a keyboard with small, flat, square keys (usually referred to as the 'chicklet' keyboard) and a gray-colored case, the CoCo 2 brought with it a more 'modern' off-white case and a keyboard with 'sculptured' keys. Some describe these early CoCo 2 keyboards as having keys which appear to be 'melted'. The travel distance of said keys is fairly low, as with the chicklet keyboard.

Upgrading your CoCo 2

CAUTION! DO NOT ATTEMPT TO UPGRADE ANY CoCo RAM OR ROM WITHOUT FIRST SECURING SPECIFIC UPGRADE INSTRUCTIONS FOR YOUR MACHINE!

Please note that improper upgrade attempts have been known to destroy the majority of the chips in a CoCo!

RAM

Note also that the RAM chips used in the 16K CoCo 2 are not the 4116s which one might have expected. The 4116 requires additional power supply voltages not supplied by the CoCo 2. Therefore, a special 16K by 1 bit RAM chip requiring only +5VDC is used. This chip has the Tandy house number 8040517.

The RAM used in most 64K CoCo 2s consists of standard 4164 chips.

CoCo 2 RAM upgrade information may be found below in the sections specific to each 16K CoCo 2 version.

ROMs

Like the original Color Computer, the CoCo 2 has provisions for two ROMs. Each consists (in most cases) of 8 kilobytes of data in a 24-pin ROM chip :

• Color BASIC

The Color BASIC ROM is present in every CoCo. It contains the minimal BASIC interpreter and necessary routines to drive the machine's keyboard, video circuitry, and I/O ports. Most CoCo 2s use version 1.2 of the Color BASIC ROM (the two ROM versions are independent). A Color BASIC machine displays its Color BASIC version at powerup.

• Extended Color BASIC

The optional Extended BASIC ROM adds extra graphics commands and other assorted functionality enhancements. Extended Color BASIC (the composite of both ROMs) is also required in order to utilize a floppy disk controller on a CoCo. Extended CoCo 2s use version 1.1 of Extended BASIC (the two ROM versions are independent). An Extended Color BASIC machine displays its Extended BASIC version.

Those machines which shipped without the Extended BASIC ROM could be upgraded (in most cases) simply by plugging the expansion ROM into the appropriate empty socket. The remaining machines shipped with the ROM already in place.

The BASIC command 'EXEC 41175' will display the Color BASIC ROM version in an Extended Color BASIC machine.

Keyboards

Before long, Radio Shack began to offer an additional model of the CoCo 2: one with Extended Color BASIC and 64 kilobytes of RAM already installed. This machine also shipped with a newly-designed keyboard, with greater key travel than either of the previous styles. Every new CoCo 2 began to ship with this new, 'enhanced' keyboard. Note that late-model CoCo 1 chicklet keyboards, all CoCo 2 keyboards, and even CoCo 3 keyboards use the same type of mylar ribbon cables and are interchangeable.

The CoCo 3 keyboard (and some third-party designs) utilize previously-unused positions in the CoCo's keyboard matrix, adding several new keys. Appropriate software can make use of the extra keys on any CoCo model. Note that the style (appearance, key travel, etc.) of the CoCo 3 keyboard is identical to that of the later CoCo 2 keyboard, with the exception of its extra keys.

Labels as an indication of model differences

Radio Shack switched, during the production of the CoCo 2, from the use of the 'TRS-80' label to the 'Tandy' label on its computer products. For this reason, the CoCo 2 can be found with either label. The vast majority of samples seen and possessed by the author display the TRS-80 label. The Tandy label appears to coincide accurately with yet another variation among CoCo 2 models: the presence of the enhanced MC6847T1 VDG (Video Display Generator) chip therein. Every original CoCo and the majority of CoCo 2s (those displaying the TRS-80 label) use the earlier MC6847. As its name implies, the VDG generates the CoCo's video output. The plain 6847 version contains only uppercase characters in its internal character set, whereas the 6847T1 also contains lowercase characters. Note that software and hardware solutions have been created to overcome this limitation of the 6847, without which lowercase characters are displayed as reverse-video uppercase characters. Conversely, while the 6847T1 is capable of generating true hardware-based lowercase, that capability is seldom exploited.

NOTE: Information is still being compiled and confirmed about the various models, particularly those in the A- and B-series. Updates will likely be forthcoming......

References

• http://users.digitalindigo.net/techno/coco2.html
• https://web.archive.org/web/20150325023609/www.tandycoco.com/coco2.shtml