Help needed with EDC SR-99 Drum Machine

[NerveJam]

I decided to have a go at fixing my broken EDC SR-99 drum machine.
This is different to both the dr-55 and sr-88 machines, so the schematics aren't that much use. (the '99 is more complex)

The problem is that I can't get the damned thing to go into 'pattern write' mode. It stays in "play" mode, and the start/stop buttons just do exactly that, ie not program sounds.
I have replaced the 4011 (although it's socketed and the socket may be dodgy -someone else did that..) and also the TC5514 memory chip. (That's now in a socket, too) No luck.

I cannot find a schematic or service manual for the sr-99 anywhere.. can anyone help, or point me in the right direction?

Thanks.

[NerveJam]

Here's a link to my blog about this project: https://synteknik.com/projects/current-projects/edc-sr-99-project/