Got a Alesis SR-16 Drum computer from a friend of mine. The machine didn’t work, it only show 8 blocks on the display.
Revision: Rev D
Let’s find the problem
First I tested the voltage regulators VR1 (7805) and VR5 (7905), they both outputing the right voltage levels (5V and -5V).
Next I tested the reset line of the SC80C31 cpu, the reset line is low, so the processor is in a reset state and because of that not working.
Next I checked the resonators Z1 (12MHz) and Z2 (8MHz), Z2 was output a 8MHz clock but Z1 sometimes was outputing 12MHz, but the clock was interupted often.. so very unstable..
I didn’t have a 12MHz resonator or oscilator, so I decided to put a 8MHz crystal oscillator, and the clock is stable on 8MHz the display output looks good.. YEAH!
Sound is pitched
Machine is working again display output is good.. BUTTTTTT sound (sample) output is a pitched. First I thought it was because of the change of oscillator, but the pitch didn’t changed after putting a 16MHz onthe Z1 spot, so the sample output has a different clock, I guess.. Z2..
I measured Z2.. Seem the resonator is running at 40MHz.. but that is should be 8Mhz..
I replaced the Z2 resonator it with a 8MHz crystal oscillator.
Let’s see if the audio pitch is normal again..
That sounds good, so that’s fixed..
Both resonators are broken, don’t ask me why but they weren’t running at the speed they should do.
Z1: 12MHz resonator is broken, ordered a new one, and will replace it next week.
Z2: Replaced it with a crystal oscillator
Z1 is replaced with new 12MHz resonator. and it works perfectly!