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Tandy Coco unboxed!

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bettablue

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Joined
Feb 21, 2011
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Eugene, OR
Well, it arrived today! My best friend bought me a very nice looking Tandy Coco through E-Bay last week. It was delivered today! This was the very first computer I ever owned, so I was quite excited to see the old beauty. Needless to say, I was somewhat underwhelmed. Not at the PC, or lack of some miscelaneoud bits and pieces, but at the sellers lack of proper shipping! I'm really surprised that it arrived in one piece! There was almost nothing in the way of padding between the computer and the outer box. and other than the computer cover, there were only a couple of pieces of cardboard to keep it from being toally destroyed. There was absolutely nothing keeping it from moving side to side though.

However, it looks like I got lucky. The computer is in one piece afterall! Now I need to get a couple thing for it. Currently I have no way to connect it to a TV, or monitor. And, there are no game controllers, or game cartridges. So, I guess a bit of shopping on E-Bay, and Amazon are in order.

I do have a question though. I understand that by taking pin 1 an 4, and connecting them directly to an RCA plug at the other end of the cable, I can bypass an RF converter. Can I do something similar to connect the Coco to a standard VGA computer monitor? Or is there a cable I can either use or make that will allow me to connect to an input on my TV?

One more question: Can I use the same cable and converter from my Commodore VIC-20/C-64? And can I do the same with it to connect to the TV/monitor?

I realize I'm asking for a lot, but right now, I can't connect the Coco, nor my Commodores to a TV because of line noise. I suspect a bad RF converter.

Thanks much everyone. I'll hve pics to post both here and on my web site as well in a couple days. I want to get some before and after shots. The computer is pretty dirty, so it will need to be cleaned.

Thomas
 
bettablue said:
I do have a question though. I understand that by taking pin 1 an 4, and connecting them directly to an RCA plug at the other end of the cable, I can bypass an RF converter.
Click to expand...

Pin 1 and 4 where?

I'd have to find a schematic to figure out exactly where in the CoCo a composite signal is available, as yes, there is one that can be tapped upstream of the RF converter circuitry. But in every "Composite conversion" I've seen for the original CoCos the conversion includes adding a small parasite circuit board with an amplifier on it, because otherwise the resulting signal would be unacceptably weak. There are no external connectors on the CoCo where you can just tap out a composite signal.

(I'm thinking perhaps you may be confusing the CoCo for the Tandy Model I? The Model I uses a 5 pin DIN plug similar to that on the back of Commodore 64s for its video output, and can indeed be simply tapped to use a generic composite monitor in place of the modified B&W TV Tandy sold with it.)

What are you using for a TV switchbox? If it's an ancient 300 ohm (screw terminal) one connected up via a 300/75 ohm converter then it will indeed produce an incredibly lousy signal. (I'd also recommend using, if at all possible, an old CRT TV. Anything with RF looks terrible on a digital TV.)
 
... wait. Something said in the other thread is bothering me, the thing about the "coco" having a "real keyboard ". Are you positive you bought a CoCo and not a Model I?
 
Yeah, it's a real Coco. Model 1, silver. From what I've seen the Coco not only came in two colors, but also had 2 different key types. One was that goofy sensor type, and the other almost like a chicklet. I think I mislabeled the keyboard in the other post, so thanks for catching that. The keys on my Coco are definitely raised above the main body of the computer. I've also seen a mod where someone exchenged all of the keys on one of these with Cherry Browns. But I think he did a lot more than just a keyboard modification to make that work. It's long gone too. It hit the trash after a fire in his home some 15 years ago. So sorry, no pictures.



Eudimorphodon said:
... wait. Something said in the other thread is bothering me, the thing about the "coco" having a "real keyboard ". Are you positive you bought a CoCo and not a Model I?
Click to expand...
 
Aaaaah. Okay.

I don't think tandy ever made a full-up matrix keyboard Ala the Atari 400... people did gripe about the chicklet, but personally I never thought it was that bad. The keys may have lacked sculpting but at least they were spaced correctly.

I regularly lampoon Apple for ripping off the design of the original coco for their current lineup. Silver case? Check. Black trim? Check. Chicklet keys? Double-check....
 
Thanks for the recomendation. However, the use of an older TV is out of the question. My wife just bought me a pretty nice LCD TV for my vintage computer room. I do think you're correct in your thinking about the Tandy 1 though. Looking at the Coco, it has what appears to be an RCA output. Now my Commodores also use some kind transformer between the computer and the RF converter. I was thinking of somehow taking the cable that connects to the TV via the RF adapter, and eliminating the switchbox by replacing the switchbox with an RCA connector, then using and adapter plug to connect directly to the TV's cable unput. That would eliminate a lot of the noise associated with the open antenna circuittry.

Any ideas on how to make such a beast? To me it sounds simple enough. With my fair amount of soldering experience, and once I have all the pieces, I should be able to work one up in about 10 minutes or so.

Are there any directions anywhere for this cable's construction?

Thanks again.

Eudimorphodon said:
Pin 1 and 4 where?

I'm thinking perhaps you may be confusing the CoCo for the Tandy Model I? The Model I uses a 5 pin DIN plug similar to that on the back of Commodore 64s for its video output, and can indeed be simply tapped to use a generic composite monitor in place of the modified B&W TV Tandy sold with it.

What are you using for a TV switchbox? If it's an ancient 300 ohm (screw terminal) one connected up via a 300/75 ohm converter then it will indeed produce an incredibly lousy signal. (I'd also recommend using, if at all possible, an old CRT TV. Anything with RF looks terrible on a digital TV.)
Click to expand...
 
By antenna input I meant cable input.
You should just need a hunk of coax, a F-type connector on the TV end, and a RCA plug on the CoCo end. All should be available at RatShack.
patscc
 
In your other thread I linked to a picture of a pre-made RCA-jack-to-Coax plug adapter. It's a *slightly* strange item but there's a reasonable chance you could get one off the wall at Radio Shack. (Or other local electronics/hardware store.) I'd probably go with that and a plain video-quality RCA patch cable myself. But rolling your own cable should work too. I'd probably start with a pre-made cable TV patch cable, cut one end off it, and solder the RCA plug in its place, just to save a step.
 
I have gotten superior results when using an old-fashioned RF switchbox, instead of the RCA-to-RF plug adapters that everyone is recommending these days. The reason is because an RF switchbox has impedance matching transformers (baluns) inside it while the plug adapter does not. I did back-to-back comparisons with my Atari 2600 and the switchbox resulted in noticeably less on-screen interference than the plug adapter.

What gives RF switchboxes a bad reputation is that when the TV/Game switch on them gets to be 25-30 years old, it will develop dirty contacts, which will give you a weak or intermittent signal. But a shot of contact cleaner spray, or sometimes just rapidly moving the switch back and forth, will clean up the contacts and give you a strong, clear signal on the TV again.
 
I saw that, and am looking for one right now. I'm stuck at home in a wheelchair, so I have to do most of my shopping online. But the idea of taking a pre-existing cable and modifying it to make the final connection seems a lot easier than "rolling, your own" as you put it. ;-)

Also, I'm thinking of a way to connect both my Commodore C-64 and Coco to the same LCD TV. I could use a switch box. But since I really only have room to show off one or the other right now, I want something that I can sort of mount on the side or front of the TV/Microwave cart so that I can connect either my Commodore or the Coco to the TV's tuner. Also, switch boxes are great for leaking signals, or even picking up stray signals which will destroy the computers output. Personally, I would love something to connect everything to an RCA composite on the back of the TV! But then again, that will definitely require a signal amp. I'm not that good at electronics to make my own signal amplifier.


Eudimorphodon said:
In your other thread I linked to a picture of a pre-made RCA-jack-to-Coax plug adapter. It's a *slightly* strange item but there's a reasonable chance you could get one off the wall at Radio Shack. (Or other local electronics/hardware store.) I'd probably go with that and a plain video-quality RCA patch cable myself. But rolling your own cable should work too. I'd probably start with a pre-made cable TV patch cable, cut one end off it, and solder the RCA plug in its place, just to save a step.
Click to expand...
 
Nice thought. I was attempting to use my Commodore with it's switch, and the signal was horrible. It seems to be picking up some errant signal and intrducing noise, which is why I thought eliminating the switch would be the way to go. Again, I wish all of the all-in-one computers had composite output jacks for both audio and video. That would have made things so much simpler.


bettablue said:
I saw that, and am looking for one right now. I'm stuck at home in a wheelchair, so I have to do most of my shopping online. But the idea of taking a pre-existing cable and modifying it to make the final connection seems a lot easier than "rolling, your own" as you put it. ;-)

Also, I'm thinking of a way to connect both my Commodore C-64 and Coco to the same LCD TV. I could use a switch box. But since I really only have room to show off one or the other right now, I want something that I can sort of mount on the side or front of the TV/Microwave cart so that I can connect either my Commodore or the Coco to the TV's tuner. Also, switch boxes are great for leaking signals, or even picking up stray signals which will destroy the computers output. Personally, I would love something to connect everything to an RCA composite on the back of the TV! But then again, that will definitely require a signal amp. I'm not that good at electronics to make my own signal amplifier.
Click to expand...
 
Luckily your Commodore 64 has either a five or eight pin DIN plug on the back that you *can* tap a better signal from. If it has the 5 pin plug you can get composite video and audio from it; if you have the 8 pin DIN S-Video is an option. Either will jack straight into your LCD TV and provide a much better looking picture.

Here's a couple links showing the wiring needed for S-Video.

And here's a page showing the pinout of the older 5 pin connector, in case you have a more elderly C-64.

Regarding impedance matching on the RF cable, I was actually wondering if that might be an issue with the straight-through plugs. (I haven't tried one myself, but I've seen them recommended.) If that's the case then I'd probably suggest for best results finding a switchbox that offers direct 75 ohm output and, as noted, cleaning up the contacts. (Or possibly you could crack it open carefully and just bypass the switch, if you don't care about being able to switch it.)
 
The Coco I just got is the silver "Mid" release. It has a fairly low serial number too, 576XXX. Looking at the connector, I see what looks like a FEMALE RCA plug. I guess I could make a simple straight cable with an RCA connector on one end, and a type F connector on the other. Would the center line from the RCA be the center of the type F as well? I could try trial and error, but I don't like the error part.

I was also thinking of trying to locate an original cable to connect the Coco to a TV too. Then I'll think about making a new cable set after I've had time to analyze the circuitry for putting one of them together with the single adapter that patscc recommends.

For my next trick, I want to get the final piece on my wish list. The original TRS-80 Micro Computer-Series 1. It would be nice to find one with the original RCA monitor and tape recorder intact, but I won't hold my breath. I'll settle for the keyboard/computer portion, and hope the original cables for connecting to a B&W TV is still there. Manuals would be a serious plus.

I have a pretty good histoery with the TRS-80, some good stories, and some not so good. But it was the TRS-80 that I wrote my first programs on. I even got paid to write code on the computer for several of my customers while working for Radio Shack during 1976 to 1979. This is the one that really got me started.

So, if anyone has an original cable set for sale; please send me a PM.

Thanks much.

Eudimorphodon said:
Luckily your Commodore 64 has either a five or eight pin DIN plug on the back that you *can* tap a better signal from. If it has the 5 pin plug you can get composite video and audio from it; if you have the 8 pin DIN S-Video is an option. Either will jack straight into your LCD TV and provide a much better looking picture.

Here's a couple links showing the wiring needed for S-Video.

And here's a page showing the pinout of the older 5 pin connector, in case you have a more elderly C-64.

Regarding impedance matching on the RF cable, I was actually wondering if that might be an issue with the straight-through plugs. (I haven't tried one myself, but I've seen them recommended.) If that's the case then I'd probably suggest for best results finding a switchbox that offers direct 75 ohm output and, as noted, cleaning up the contacts. (Or possibly you could crack it open carefully and just bypass the switch, if you don't care about being able to switch it.)
Click to expand...
 
Last edited:
This will be my final question for this thread.

Is there a way to add more RAM to the Coco 1? I thought there was originally. And to be honest, I'm not even sure what my Coco has as far as rexources just yet. I have yet to locate the correct operators manuals, users guides, and technical references.

Thanks again.
 
The original CoCo came in 4k, 16k, and "32k" (actually 64k but BASIC can only see half of it) versions. You can determine the amount you have by typing "print mem" at the Basic prompt. The exact answer will depend on whether you have "plain" or Extended Color Basic but will be in the ballpark of 2.5k, 14k, and 30k for non-Extended and around 6k less for Extended. (Extended sets aside 6k for high-res graphics memory when it powers up, on top of the 512 bytes of text memory and roughly 1k of housekeeping space that Color Basic uses.)

The power-on message above the "OK" prompt will tell you whether you have extended BASIC or not. Memory expansion involves removing the existing chips, replacing them with higher-capacity versions, and adjusting some jumper/solder points on the circuit board. Really early CoCos don't support the 32/64k option without some hacking. (Once upon a time people upgraded those by piggybacking a second set of 16k chips on top of the first 16k, instead of the canonical way of replacing the 16k DIPs with 64k.)
 
Quoted from Eudimorphodon: "Memory expansion involves removing the existing chips..."

That makes sense, and also explains why when a customer wanted a memory upgrade, the had no real choice in the beginning, other than to take the computer to the nearest Radio Shack store, to have it shipped back to Tempe for upgrades. While working at Radio Shack I had to send a lot of systems back to Tempe for upgrading even before the customer could take his computer home. :chainsaw:

Getting back on track... :ashamed:

My particular Coco is one of the mid release 1st generation units (Based on the centered location of the Tandy Color Computer logo, and lack of matching memory logo sticker on the top right of the case) do you think my Coco 1 can eventually support the full 32 or 64K. Where do you suppose I could have that done? My electronics skills are definitely not good enough to perform that kind of memory upgrade. How much do you suppose that upgrade would cost me? (I'm sorry, but your answer just opened up a whole new can of worms. But depending on the answers will close up that can pretty quickly.) Will the limited memory also limit the additional hardware I might eventually add onto the system, like printer, and external floppy drive etc.? What other peripherals are there for the Coco any way?
:medic:​

Personally, I look forward to many years of servive from this small unnassuming little silver/gray computer. I want to personally say "Thank You" Eudimorphodon. You have been especially and extremely helpful. I had forgotten so much about these machines, and you've already help clear my muddled memory of working with these beautiful old ,achines. My Coco is already a welcome addition to my vintage computer collection.
:toast2:​

Soon, it will join the others as my business partner and I take my vintage computer collection to area schools for classroom presentations. More on that later.
:bigparty:​

Thanks to everyone else who hass graced this thread. You have all been fantastic.
Eudimorphodon said:
The original CoCo came in 4k, 16k, and "32k" (actually 64k but BASIC can only see half of it) versions. You can determine the amount you have by typing "print mem" at the Basic prompt. The exact answer will depend on whether you have "plain" or Extended Color Basic but will be in the ballpark of 2.5k, 14k, and 30k for non-Extended and around 6k less for Extended. (Extended sets aside 6k for high-res graphics memory when it powers up, on top of the 512 bytes of text memory and roughly 1k of housekeeping space that Color Basic uses.)

The power-on message above the "OK" prompt will tell you whether you have extended BASIC or not. Memory expansion involves removing the existing chips, replacing them with higher-capacity versions, and adjusting some jumper/solder points on the circuit board. Really early CoCos don't support the 32/64k option without some hacking. (Once upon a time people upgraded those by piggybacking a second set of 16k chips on top of the first 16k, instead of the canonical way of replacing the 16k DIPs with 64k.)
Click to expand...
 
bettablue said:
My particular Coco is one of the mid release 1st generation units (Based on the centered location of the Tandy Color Computer logo, and lack of matching memory logo sticker on the top right of the case) do you think my Coco 1 can eventually support the full 32 or 64K.
Click to expand...

The CoCo 1 came with several different motherboard revisions. There really isn't a 100% reliable way to tell which one you have without looking at the board itself; the first two versions, the "C" and "D" boards, don't support the 4164 chips necessary for a 32/64k upgrade without major surgery (I think there may have been an article on how to do it in "80 Micro" magazine). For the "E" and later boards it was just a chip swap and move some jumpers.

If you do have a C/D board I'd suggest not upgrading it beyond 16k; you can take a 4k to 16k without damaging it, but beyond that... given the fairly low going price of CoCo 2s with 64k I'd probably say just buy one of those instead of upgrading the old gray mare.

Where do you suppose I could have that done? My electronics skills are definitely not good enough to perform that kind of memory upgrade. How much do you suppose that upgrade would cost me? (I'm sorry, but your answer just opened up a whole new can of worms. But depending on the answers will close up that can pretty quickly.) Will the limited memory also limit the additional hardware I might eventually add onto the system, like printer, and external floppy drive etc.?
Click to expand...

If it's an E-board or newer and the memory is socketed anyone who's comfortable pulling chips could probably do it for you. (They just need to know to also change the jumper.) If you *really* wanted to hack more RAM into a C/D board by either converting it to the functional equivalent of an E or by piggybacking RAM then some soldering experience would definitely be a plus... and you'll have to track down the instructions. I *think* you also have to upgrade the Color Basic ROM in an early CoCo for the 32k/64k upgrade so it will program the SAM chip correctly. You don't need the BASIC upgrade for the piggyback method, but the piggyback method is a serious hack that involves irrevocable modifications to your machine.

So far as limiting additional peripherals, if you want to use a disk drive you need at least 16k *and* you need to have Extended Basic. (Color Basic already has printer support.) You could add Extended basic to a 16K or better gray CoCo by plugging in a burned EPROM if you don't already have it (not sure offhand if you need any sort of socket adapter for an EPROM to work instead of the factory mask ROM), but... this is another case where it might just be better to get another CoCo that already has 64k and ECB.

What other peripherals are there for the Coco any way?
Click to expand...

There were joysticks, mice, graphics pads, X-10 power controllers, video digitizers, plotters... all the usual home computer toys. Making good use of peripherals that plug in via the cartridge slot usually calls for the purchase of a "Multi-Pak" expansion box. (Owning a Multi-Pak was probably the best way to distinguish a *serious* CoCo user from a casual one.) I'm sure you could spend a lot of money on eBay collecting them all.

So have you had a chance yet to actually power the thing up and see what you got?
 
I powered it up today to find out how much memory it has, and to see which version of BASIC it's running. There is a little over 8K of usable memory available to work with, and it is running Extended Color Basic. So that's something positive. However 8K of memory is only about half of what my old series 1 Coco had. 16K would be just about right for what I want to do with it now. Alas, there's nothing I can really do about that though except buy a Coco 3 later on. (Which I mayor may not do).

I knew I should have killed the idiot thieving SOB of a cousin I had living with me at the time it went missing! Right now, I have the unit open on my work table so I can adjust the video gain slightly. Then after buttoning it up, I'll try running the system again. I know the cable running between the Coco and the TV is pretty cheap. My wife in her infinite wisdom, decided to get me an RCA cable from the 99 cent store. Oh yeah, there's going to be a lot of quality there... Still I won't tell her, because she dows try.

Later on today, I'll try to see about getting another cable of much higher quality to connect the Coco directly to the Cable input on the TV. It should be pretty clean then.

One more thing, then I'll let it drop. I've gone through all of the technical manuals, the Tech Reference guides, ets, and I don't see anything about board revisions. Can you tell me how I can tell which board revision is installed in this thing? Once I know that, I'll know what I want to do with this little beastie. I

f I do decide to sell it, I should get a lot more than my best friend paid. It looks great now that I've completely cleaned it up.

Thanks again.


Eudimorphodon said:
The CoCo 1 came with several different motherboard revisions. There really isn't a 100% reliable way to tell which one you have without looking at the board itself; the first two versions, the "C" and "D" boards, don't support the 4164 chips necessary for a 32/64k upgrade without major surgery (I think there may have been an article on how to do it in "80 Micro" magazine). For the "E" and later boards it was just a chip swap and move some jumpers.

If you do have a C/D board I'd suggest not upgrading it beyond 16k; you can take a 4k to 16k without damaging it, but beyond that... given the fairly low going price of CoCo 2s with 64k I'd probably say just buy one of those instead of upgrading the old gray mare.



If it's an E-board or newer and the memory is socketed anyone who's comfortable pulling chips could probably do it for you. (They just need to know to also change the jumper.) If you *really* wanted to hack more RAM into a C/D board by either converting it to the functional equivalent of an E or by piggybacking RAM then some soldering experience would definitely be a plus... and you'll have to track down the instructions. I *think* you also have to upgrade the Color Basic ROM in an early CoCo for the 32k/64k upgrade so it will program the SAM chip correctly. You don't need the BASIC upgrade for the piggyback method, but the piggyback method is a serious hack that involves irrevocable modifications to your machine.

So far as limiting additional peripherals, if you want to use a disk drive you need at least 16k *and* you need to have Extended Basic. (Color Basic already has printer support.) You could add Extended basic to a 16K or better gray CoCo by plugging in a burned EPROM if you don't already have it (not sure offhand if you need any sort of socket adapter for an EPROM to work instead of the factory mask ROM), but... this is another case where it might just be better to get another CoCo that already has 64k and ECB.



There were joysticks, mice, graphics pads, X-10 power controllers, video digitizers, plotters... all the usual home computer toys. Making good use of peripherals that plug in via the cartridge slot usually calls for the purchase of a "Multi-Pak" expansion box. (Owning a Multi-Pak was probably the best way to distinguish a *serious* CoCo user from a casual one.) I'm sure you could spend a lot of money on eBay collecting them all.

So have you had a chance yet to actually power the thing up and see what you got?
Click to expand...
 
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