[Coco] My coco3 gallery

[Bob Devries]

Mike Pepe said:

> Any history on this? Why'd you build that instead of buying one, etc?
>
> Did you make the PC boards yourself?

I built the clone for three reasons:
1. It was cheap to make.
2. It was available.
3. It seemed like a good idea, since I'm an electronics technician.

The schematic is exactly like the one from the Motorola microprocesssor 
manual, with the two PIA chips being added with kynar (wire wrap wire on an 
experimenter's area of the board.

The tape I/O joysticks and sound were copies of the Tandy Coco schematic, 
and added later, as was the cartridge port.

The PAL colour board was designed and built by a local electronics engineer. 
It was a cow to align, but worked fine once it was going.

There was also a locally designed and built disk controller, based on the WD 
2793 controller, and a modified Disk Basic 1.0 ROM. Things like auto line 
numbering, machine code monitor programme, and a few other things I can't 
remember. It had a fix for the head banging bug that DECB1.0 had. (DECB 
assumed that disk drives reset themselves to track 0 when powered up, but 
most newer drives at the time did not do so, and a subsequent seek to track 
17 for the directory, would bash the head into the end stops).

The 2793 disk controller required an oscilloscope to align it, which was a 
bit of a drawback for some people, but I had (have) access to such a beast, 
so I could do it easily.

The PCB for the main part of the computer was double-sided, but *not* 
through-hole plated. They were available for sale from an engineer I knew, 
but made by a local PCB manufacturer.

The Case Changer kit was indeed a direct copy of the schematic in the 6847 
datasheet, with switches added to enable/disable some functions. It had 
reverse video on/off, true lowercase on/off (can't remember what the third 
switch did).

--
Regards, Bob Devries, Dalby, Queensland, Australia

Isaiah 50:4 The sovereign Lord has given me
the capacity to be his spokesman,
so that I know how to help the weary.

website: http://www.home.gil.com.au/~bdevasl
my blog: http://bdevries.invigorated.org/

----- Original Message ----- 
From: "Mike Pepe" <lamune at doki-doki.net>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Saturday, August 26, 2006 12:54 PM
Subject: Re: [Coco] My coco3 gallery


> Hi Bob,
>
> Nice work there!
>
> Any history on this? Why'd you build that instead of buying one, etc?
>
> Did you make the PC boards yourself?
>
> I like the lowercase kit, looks like the circuit described on the 6847 
> data sheet.
>
> -Mike
>
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