Saturday, May 23, 2015

CoCo 3 and 512k of ram!

It's here, my brand-spanking-new (to me) Tandy Color Computer 3!  It came as a standard model, so it only had 128k, but as I mentioned in my previous post, I had also ordered a 512k ram upgrade.  Coincidentally, my memory upgrade (and 6309 cpu, more on that below) happened to come today as well.  So I turned on the CoCo3 long enough to test it (everything seems to work), then started to remove the top to install my 512k module.  
And that's where my first problem popped up.  The case is actually pretty easy to remove, just 5 screws on the bottom and the top pops right off.  Or at least it's supposed to.  You can't really see it in the picture to the right, but the white top of the case fits on the board around the keyboard.  Around the keyboard are four cylinders connected to the top but that hold the keyboard in place.  They're not screwed there, they just rest there.  But it appears that a prior owner spilled something like glue which caused the top by the Ctrl and Right Shift to stick to the keyboard itself.  Even worse, one of the cylinders I mentioned, the one to the lower left of the keyboard, was also stuck, so the top wouldn't come off.  I couldn't figure out any way to unstick it, so I finally ended up breaking it.  That's the hole in the picture to left.  On the picture just below, if you look closely near the lower left side of the keyboard, you can see the plastic riser that used to fill that hole.  I tried to remove it without damaging the top, but after quite a while of fruitless effort, just snapped it off.

With the top finally off, I moved on to installing the memory module.  That's the 512k module in the picture to the left, the blue triangular circuit board just above the keyboard.  It was a little nerve-wracking to install, because it required removing 4 IC's and cutting two capacitors.  It was the latter requirement that made me nervous, because if I cut the wrong capacitor, it wasn't going to be easy to fix.  Putting back in an IC is easy (assuming I wasn't clumsy enough to snap off a chip leg or anything, which thankfully I was not - this time), but replacing a capacitor is not such an easy task for me, especially these because they're actually pretty small.

But fortunately it went smoothly and the memory upgrade worked without a problem.  The machine booted up as normal and gave me its standard memory output in Disk BASIC.  Of course, since that's in the neighborhood of 22k, that's not really an indicator if all 512k is available, though obviously its a good sign.  The memory module did ship with a memory test program, but unfortunately it was on a 5.25" floppy disk, and I don't have a floppy drive for the CoCo.  I have my SDC, but that requires a disk image, and for some reason Cloud 9 didn't have it available for downloaded.  But thankfully a quick Google and I had the disk image.  A little amusingly, the program was written to use 80-column text mode, which turned out to be all but unreadable on my screen.  Fortunately, it was readable enough for me to confirm that it had found all 512k.

So the other upgrade I purchased was a 63x09E cpu to replace the 6809.  Unfortunately, once the top was off, I realized that the 6809 is soldered on the motherboard, not socketed, so I'll have to desolder the existing cpu.  Looking back at the Cloud 9 page, I do see where it clearly says that, but I must have missed that.  I'm reasonably confident that I can remove it, but after struggling with the case, I decided I wasn't in the mood to tackle the cpu.  In any case, I want to wait until I can get a socket since I'll want to use that instead of soldering the new cpu directly to the motherboard.

So with that, I put the top back on and now I have a nice CoCo 3 with 512k of ram.  I did notice that the Right Shift is a little finicky, but that's a minor problem at best.  It does work, but you just really need to press it firmly.  Not sure about the Ctrl or Alt keys yet.  I press them while in Disk BASIC and a @ and = show up.  I don't know if this is normal behavior, but that's what happens in MESS when I type those keys, so I assume so.

As you can see from the photo, the hole is still visible, though it's not too bad.  At least I won't have to wrestle with the case again, when I finally get up the energy to replace the cpu.

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