Ensoniq EPS keyboard issue

[gkmaia]

I bought a second hand EPS (not the 16, the standard one).

Got the ALL leds no display issue.

Power supply is fine.
The keyboard to main pub cable has been re-crimped.
MC68000 MPU seems to be managing the control, address and data bus.
MC68440 DMAC seems to be also doing its job pulsing addresses.
27C256 EPROMs are getting address calls and shooting data.

If I unplug the keyboard PCB and type on buttons the display place the characters only on the first column.
If I plug the keyboard PCB back and type on buttons the display then place one character per column.
Seems the keyboard PCB is alive in some way.

If you look at the attached screen you will see the 68000 try to call the buses with repetitive routines for a couple seconds then goes quite. But it does not bring RESET or HALT low.

My suspicion is that the processor is not getting valid boot instructions from the EPROM and then goes quit. But never deal with this keyboard before so not sure how it behaves.

Anyone out there with some reasonable experience at the EPS component level or MC68000 to give me some hints?

 

[rjenkinsgb]

Hi,
I'm very familiar with the 68000 but not that specific keyboard.

I have found a copy of the schematic on archive.org, here: http://ia800704.us.archive.org/26/items/sm_Ensoniq_EPS_Schematics/Ensoniq_EPS_Schematics.pdf

The 68000 loads it's initial reset info from address 0 in memory space; 00000000 for the stack pointer and 00000004 for the program counter.

http://wiki.neogeodev.org/index.php?title=68k_vector_table

However, according to the memory map info in the scheatic, that setup has RAM starting at 00000000...
There must be something in the hardware to switch it to a ROM address during reset ?

Edit - more technical info on the EPS.

Ensoniq Technical Documents and Schematics - R-Massive

zine.r-massive.com

 

[gkmaia]

Thanks for the technical info on the EPS. Very useful. I going through it at the moment.