Construction just beginning...Construction just beginning...
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).
Please note that improper upgrade attempts have been known to destroy the majority of the chips in a CoCo! 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.
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.
Like the original Color Computer, the CoCo 2 has provisions for two ROMs: Color BASIC and Extended BASIC. Each consists (in most cases) of 8 kilobytes of data in a 24-pin ROM chip. 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. 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. 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. Note that most CoCo 2s use version 1.2 of the Color BASIC ROM, and all Extended CoCo 2s use version 1.1 of Extended BASIC (the two ROM versions are independent). A Color BASIC machine displays its Color BASIC version at powerup; an Extended Color BASIC machine displays its Extended BASIC version. The BASIC command 'EXEC 41175' will display the Color BASIC ROM version in an Extended Color BASIC machine.
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. Before long, 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.
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.
As implied previously, many versions exist of the 'Color Computer 2'. The following summary attempts to reveal the specific traits inherent in each such variant, organized by Radio Shack catalog number. Note that this list is likely not yet complete, and has not been totally verified.
26-3026
This is the first model of CoCo 2. Built in the USA, it came equipped with 16 kilobytes of RAM, Color BASIC only, and the 'melted' keyboard. 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.
(Note that this same model number has reportedly been found on larger, Korean-made CoCo models in Australia.)
26-3027
This machine is identical to the 26-3026, with the exception that it already has the Extended BASIC ROM factory-installed.
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 labeled W1. W1 is located between U6 and U7.
26-3127
This is the first '64K Color Computer 2'. It contains the Extended BASIC ROM, the 'enhanced' keyboard, and 64 kilobytes of RAM (naturally). Otherwise, it is identical to the 26-3026/26-3027. 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 of the author.
26-3134
This 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.
26-3136
This machine is identical to the 26-3134, but with the Extended BASIC ROM factory-installed.
To upgrade the 26-3134 or 26-3136 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 labeled J1. J1 is located next to IC7.
26-3134A
This is the next Korean 16K Color BASIC CoCo 2. It utilizes a #20261044 circuit board, which differs considerably from the previous versions. This board's RAM is in the form of two socketed 4416 chips. The preferred 64K upgrade for this board involves replacing them with two 4464 chips. However, the option exists (by means of several special connectors on the board) of a factory upgrade consisting of eight 4164 chips on a daughterboard. 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.
26-3136A
This machine is the 16K Extended BASIC version of the 26-3134A. It uses a single 28-pin, 16-kilobyte ROM containing both Color BASIC and Extended BASIC.
26-3134B
This 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 daughterboard 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).
26-3136B
This machine is the Extended BASIC version of the 26-3134B.
To upgrade a 26-3134A, 26-3136A, 26-3134B, or 26-3136B to 64 KB of RAM, it is necessary to replace the two 4416 chips with 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.
26-3127B
The last model number associated with the 64K Extended BASIC CoCo 2, this is an odd one indeed. The author has no less than three distinctly different machines, each bearing this exact model number. One is a USA-made TRS-80 with a #20261044 board and a 6847, one is a USA-made Tandy with a #20261058 board and a 6847T1, and one is a Korean-made Tandy with a #20261058 board and a 6847T1. 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.
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......
Last updated: 22 March Y1.999K
to
return to my home page.
