Just a quick update:
What was causing this error was the dead RAM memory chip which has a battery built-in. I was able to find a memory RAM chip replacement for my DSP4500. I looked for the original part number BQ4013YMA-120, but it was not available in Mexico. Luckily, in this forum I found out that there is another Ram chip part number that also works: DS1245Y-120+ and has the advantage of being non-volatile RAM memory, so there is no battery built-in and it won´t die again.
I was able to get this part from Mouser Electronics in Guadalajara, which was imported from Mouser Texas (by the way, the customer service of Mouser Electronics is top notch, very kind and committed people). Then I had it replaced by the best area expert in audio systems, who happens to be an electronics engineer and a terrific guitar player (Thanks Humberto Fierro!) and after his magic work on the unit it came back to life with no more errors and now is working as new.
