Using the Tandy Color Computer 3 with an RGB monitor

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Bill Loguidice's picture

The classic Tandy Color Computer (CoCo) series of computers featured only RF output right up until the release of the CoCo 3, which features not only RF, but also much needed color composite (mono audio) and RGB outputs. While composite is superior to RF and compatible with legacy software, for optimal use of supported CoCo 3-specific modes and software, you'll obviously want the superior RGB connection, which is incredibly sharp in comparison to the other two options. The catch with the RGB output is that the connector is non-standard and doesn't necessarily work with a wide range of monitors. (read more)

The RGB out on the CoCo 3 is found on its underside

Luckily, if you do have one of its supported monitors, you can still get these non-standard video cables directly from Cloud-9, listed under "Hardware" and "Modular Video Cable." Cables are sold that work with the standard Tandy RGB Color monitors, Magnavox 8CM515, NEC Multisync 3DS, and, likely the most widely available and versatile vintage monitor, the Commodore 1084, which typically supports four or more different video modes/inputs. The Magnavox, NEC, and Commodore cables mate to the "CoCo 3 Video Monitor Adapter Cable," which is the only cable you need to work with Tandy RGB Color Monitors like the CM-5. In other words, if you have anything other than a compatible Tandy RGB monitor, then you'll need to purchase two cables from Cloud-9 instead of just the one.

The "CoCo 3 Video Monitor Adapter Cable" mated to the "Commodore 1084S Monitor Cable DB-9 Mating Cable"

In any case, I'm lucky enough to own three Commodore 1084 monitors, as well as a few of the Tandy RGB monitors. What I always find interesting - and this is not news to those familiar with Commodore's monitors - is that there are actually a surprising number of variations in the Commodore 1084 monitor series. Some work with more stuff than others, and some have different connection options and features than others.

The CM-5 and its built-in male cable

I had no issue with using the "CoCo 3 Video Monitor Adapter Cable" with the Tandy RGB Color Monitor CM-5. The female connector on the cable mated perfectly to the male connector on the CM-5.

The Commodore 1084S-D1 has a flat RGB connector with a female input.

The 1084S-D1 has a flat RGB connector with a female input
Unfortunately, the supplied combination of "CoCo 3 Video Monitor Adapter Cable" and "Commodore 1084S Monitor Cable DB-9 Mating Cable" results in a similar female output. That's where a simple gender changer comes in, which I got on Amazon, and is called the Slimline Serial DB9 Gender Changer - M/M (GC9SM).

With the gender changer, I was able to get it to work, though you'll likely have to fiddle a bit with the screws on the gender changer and the posts on the input on the back of the monitor to make a solid connection.

I then tried the same thing on the Commodore 1084S-D2, which has a similar flat female input to the D1.

The 1084S-D2 also has a flat RGB connector with a female input
Unfortunately, the D2 could not seem to lock down the picture. Not even close. I can only assume that there's something about the D2 versus the D1 that means it's not compatible.

I then decided to grab my childhood Commodore Amiga monitor, the Commodore 1084S-P, which has a round connector as its TTL RGB input instead of a flat one. Fortunately, since I was the original owner, I still had the Commodore 128 monitor cable that it came with, which connects to that round connector and terminates in a male end. Therefore, I was able to use the "CoCo 3 Video Monitor Adapter Cable" and "Commodore 1084S Monitor Cable DB-9 Mating Cable" without needing to change the gender by simply plugging it into the Commodore 128 cable. Needless to say, it displayed the RGB output coming out of the CoCo 3 perfectly. As they say, two out of three ain't bad.

The front and back of the 1084S-P, and the Commodore 128 monitor cable. Note that this combination does not need the gender changer.

So, I'm sure an obvious question arises. Why go to all of the trouble with the Commodore 1084 monitors when the Tandy CM-5 works just fine (NOTE: I did not test my one other Tandy monitor, whose model slips my mind; it could also be a CM-5, but I don't want to check at the moment)? The CM-5 is actually a nice monitor, with a sharp picture, but it only has the one connection and no audio input. The 1084 series on the other hand, has multiple inputs and built-in sound, with some models supporting both stereo and headphone outputs. So this means that, for example, my 1084S-P can accept both composite output from the CoCo 3, as well as RGB, which I can switch between at the press of a button, while getting sound when in either input. This eliminates the need for two displays to support all software, as well as the need for any type of dedicated sound system. In fact, with the type of collector that I am, that same 1084S-P will work with dozens of the platforms in my collection. I even recently got a SCART to 1084 adapter, which I'll try shortly (I usually go SCART to HDMI, but this will be even better). In short, going the 1084S-P route is ideal.

Unfortunately, in my testing, I discovered that the sound in my 1084S-D1 is shot, and of course the D2 seems to have reduced compatibility. So, despite the countless hours I've put on my 1084S-P monitor from using it all those years, it looks like it will be pressed into service indefinitely now. Hopefully the picture tube holds up to several more years of use.

Finally, I'd be remiss not to mention the book I wrote with Boisy Pitre on the history of the Color Computer, titled, CoCo: The Colorful History of Tandy's Underdog Computer. If you appreciated this post, I'd appreciate you also checking out our critically acclaimed book in kind. Even better, kindly leave a review on Amazon or otherwise help spread the word. Every review and word-of-mouth mention helps.

Did the above work the same for you? Have you had a completely different experience? Let us know.


Bill Loguidice
Bill Loguidice's picture
Joined: 12/31/1969
The final result of the blog post

Here is a quick video of the rare real disk version of The Magic of Zanth (1987) running on a 512k CoCo 3 with the Speech & Sound Pak.

kelliemenendez (not verified)
I do not see this kind of

I do not see this kind of monitor. It is old but classy. But it works really well as it gives you RF output.

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