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teenix · (This post was last modified: 01-20-2020 11:39 PM by teenix.)

(01-19-2020 09:50 PM)wmax351 Wrote: That's what I was wondering when I was looking at the service manual. The rows definitely are connected. I'll open it up and see if there's any break in a trace or something like that.

Those rows and columns are used with other keys as well so unlikely to be the problem.

Do the DSP and BST keys work?

All of the keys produce an 8 bit value that is used to calculate the address in microcode to jump to and process the key.

8 bit values can also be expressed as two 4 bit hex nibbles, an upper and lower nibble. Eg DSP key is 72 in decimal or $48 in hex, 8 being the lower nibble.

The only logical explanation I can find is that all of the keys on the right side of the keyboard have lower nibbles less than 8, ie. bit 3 = 0.

The two exceptions are DSP which has 8 and BST (in the left half) which has 6.

If this is the case then as mentioned by Bob, maybe a ROM has failed.

cheers

Tony