[Coco] WTB Orchestra 90 cartridge

RETRO Innovations go4retro at go4retro.com
Mon Aug 1 00:06:04 EDT 2016

On 7/27/2016 2:13 PM, Zippster wrote:
> Hi Mark,
> I only have one Orch 90 cartridge myself, but on a related note, I’m doing a
> compatible “remake” of the cart.
> I was inspired by the news that Pere Serrat had reworked the Orch 90 ROM
> to make it compatible with Dragon computers.  This board is meant to support
> operation in both CoCos and Dragon machines, with software for both on the
> ROM, selectable by a switch.
> It’s essentially an Orch 90 with the logic moved into a CPLD.  I designed it to
> fit the Superpak cases.
> <https://drive.google.com/open?id=0B1sgl615FlGnMEw1U1JiM1VFVUk <https://drive.google.com/open?id=0B1sgl615FlGnMEw1U1JiM1VFVUk>>
> <https://drive.google.com/open?id=0B1sgl615FlGndnkzVjVtYlJKaXM <https://drive.google.com/open?id=0B1sgl615FlGndnkzVjVtYlJKaXM>>
> I should receive prototype PCBs back very soon.+
A couple questions:

  * Looking at the schematic of the orch 90, it looks like 3 of the caps
    are non polarized electrolytics.  On your redesign, it looks like
    you swapped out for ceramic or something similar. Was there some
    reason why Tandy used the non polarized (I had not heard of them
    before perusing the schematic)
  * The r2r ladder.  I assume the original resistor networks were 1/8W
    or 1/4W Did you go with 1/4W or 1/8W on the surface mount
    replacements?  Or, did you go with something smaller?

I hate to open my sealed cart up, or I could probably answer part of the 
second question.  Anyone have hires pics of an open cart?


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