Halcyon clone WIP - CPU, speech synth, keyboard, all working!

 Here's a video showing my progress on cloning the RDI Halcyon!

Halcyon replacement power supply finished

 Since I will need to return the original power supply soon, I needed to whip up a replacement one so I could keep working on Halcyon once I've returned the original.  Here's my quick n' dirty solution that seems to work.

Halcyon v2 repair log - RAM not working correctly

So I've got far enough with my Halcyon clone project to get the CPU working properly.  I wrote a small test program to test RAM I/O and also that the second EPROM (U32) can be read properly.  Right off the bat, my test program reported a RAM test failure.

After doing some digging, I isolated the problem to pin 20 of the RAM chip not having the proper timing.  This pin is driven by pin 8 of U18, as shown here:

A logic analyzer capture of a looping RAM read/write operation revealed the following on my clone PCB:

Pin 8 was starting and ending late.  You can compare this to the original Halcyon where pin 8 much more responsive:

Being utterly confused, I decided to hook up my scope to get a better view of the problem and saw this:

Finally, I looked again at the schematic and noticed that there is a capacitor attached to this line. Doh!

The problem ended up being that C39 needs to be a 0.001uF cap, not a 0.01uF cap.  Once I replaced the cap with the proper value, things started working.

Esh's Aurunmilla hardware is now open source!

I've sold all of my Esh's clones and commercial demand is exhausted.  So I've open sourced everything I created to make an Esh's PCB clone.  You can get it here: https://github.com/rulecity/EshsAurunmilla