Coco 1 and Coco 2 (Dragon hybrid!)
Posted: Fri Feb 13, 2015 6:21 pm
Hi all,
Starting to get to the interesting stuff now ie. the machines. I have a Coco 1 and Coco 2 looking for a good home, again all I'm asking for here is enough to cover postage (especially as they are both in an "interesting" configuration).
Both of these underwent my "Coco to Dragon" conversions - see http://www.onastick.clara.co.uk/cococnv.htm which effectively replaced the original Tandy ROMS with Dragon versions & had adaptor boards fitted such that the keyboard wiring differences were mitigated. As such, they can (bar the exception of the printer port) work as a basic Dragon. My intent was to try and put them back to their original fit before posting them on here however that didn't quite go to plan...
On the original Coco 1, the conversion was never that reliable because of the messy wiring needed to get the EEPROMS wired into the PROM sockets. So I've removed this, the keyboard mod and replaced the original BASIC & Ext BASIC PROMs. This now fires up nicely as an original CoCo. However it's only reporting a 16K memory fit whereas I'd fitted it (& jumpered it) for 64K DRAMs. I'm not entirely sure why this should be the case, I don't remember there being anything else necessary for it to detect the memory fit so it's possible one of the chips has died. The one oddity which *might* be related is that I'd put a flying lead between one of the 4164 DRAMs (pin 3, the write input) and a 74LS02 NOR gate (pin 2, another input). Not entirely sure why I did this, I'm assuming it was something to do with the Dragon conversion although I didn't mention it in my original article. Having snipped it though, doesn't make any difference to the memory being reported. The other features to note about this are that the power switch doesn't work (is permanently on) and I fitted a 5-pin DIN socket on the rear which was designed to feed to a composite monitor (like the Dragon's monitor output) - that is no longer connected.
On the CoCo 2, these used EEPROMS rather than PROMS for their BASIC ROMS, so swapping over to a Dragon ROM was much easier and also much more reliable. Unfortunately I can't find the original CoCo ROM for this, so I've left it in it's "hybrid Dragon state". Seems to fire up ok.
Cheers,
Jon.
Starting to get to the interesting stuff now ie. the machines. I have a Coco 1 and Coco 2 looking for a good home, again all I'm asking for here is enough to cover postage (especially as they are both in an "interesting" configuration).
Both of these underwent my "Coco to Dragon" conversions - see http://www.onastick.clara.co.uk/cococnv.htm which effectively replaced the original Tandy ROMS with Dragon versions & had adaptor boards fitted such that the keyboard wiring differences were mitigated. As such, they can (bar the exception of the printer port) work as a basic Dragon. My intent was to try and put them back to their original fit before posting them on here however that didn't quite go to plan...
On the original Coco 1, the conversion was never that reliable because of the messy wiring needed to get the EEPROMS wired into the PROM sockets. So I've removed this, the keyboard mod and replaced the original BASIC & Ext BASIC PROMs. This now fires up nicely as an original CoCo. However it's only reporting a 16K memory fit whereas I'd fitted it (& jumpered it) for 64K DRAMs. I'm not entirely sure why this should be the case, I don't remember there being anything else necessary for it to detect the memory fit so it's possible one of the chips has died. The one oddity which *might* be related is that I'd put a flying lead between one of the 4164 DRAMs (pin 3, the write input) and a 74LS02 NOR gate (pin 2, another input). Not entirely sure why I did this, I'm assuming it was something to do with the Dragon conversion although I didn't mention it in my original article. Having snipped it though, doesn't make any difference to the memory being reported. The other features to note about this are that the power switch doesn't work (is permanently on) and I fitted a 5-pin DIN socket on the rear which was designed to feed to a composite monitor (like the Dragon's monitor output) - that is no longer connected.
On the CoCo 2, these used EEPROMS rather than PROMS for their BASIC ROMS, so swapping over to a Dragon ROM was much easier and also much more reliable. Unfortunately I can't find the original CoCo ROM for this, so I've left it in it's "hybrid Dragon state". Seems to fire up ok.
Cheers,
Jon.