Hi friends,
Well, there are good news. The Simmons woke up again !

The main problem was the IC3 (74155) which -I understand- demux some address busses and controls the four RAM chips thru the OR gates of 7432 (IC15).
It was a NOS 74155 but obviously was dead. I found it testing the signals on the ...

Tomorrow I will go to an electronics store in Barcelona to obtain the 1Mhz can oscillator and, maybe, some nowadays equivalent RAMs of the vintage HM6116 (among other hard-to-find stuff I use to buy there :). I will tell you if that produce some changes in the whole behavior of the machine.
Until ...

Ok, I didn't know that. But the time the machine woke up (years ago), the RAM's were not installed, I'm sure. Although, it shown the E1 error at the end of the pattern programming routine, as shown in the video.

Hi to everyone, and sorry for my delay.
I am overcome by such amount of info, so I will try to answer based on my limited knowledge on this topic.

It's important to say the original problem on this machine was a massive battery corrosion which invaded a large part of the CPU board. I understand it ...

Hi Friends !

I've attached the full CPU board scheme (fig.1). It was re-drawn by me, because the original one looked like a caveman painting.
In addition, I drawn the most exactly representations of digital waveforms presents in all I/Os of the R6502AP I'm using now. There are few address busses ...

First, I want to thanks for your answers, I really appreciate that.

I have a R65C02P2 and a R6502AP new ones. The reason why I'm using the CMOS one is because it is the only one that shows a behavior compatible with the "RESET" function during power up. The control panel has a large number of LEDs ...

Hi to all members, I'm Sergio, from Spain.
I'm a "most-than-a-newbie" in the 6502's world... in fact, I'm an analog technician, so I don't use to deal with microcontrollers.

I've been trying to repair for years a very strange device manufactured by Simmons, a SDS6 percussion sequencer which uses a ...