Re: Follow-up: 6502 deaths?

[Sabino Maggi <maggi@ien.it>]

"ruud.dingemans" wrote:
> 
> Rubywand wrote:
> > > Now my A2 first beeps at boot and then the usual prompt appears.
> > > It was the processor (thank Andy!)
> 
> >
> >      Thanks for posting the info on your fix!
> 
> Strange, really. I don't think fall-out rate for 6502's (compared to
> other chips) is all that big. (I had two from old Atari arcades, which
> had really been manhandled, touched with fingers, lying in a steel box,
> etc., and still they worked.

It is strange, I agree. 
I have never found a broken microprocessor, even in machines that have
been exposed to humidity, dirt, too high or low temperatures, for years. 
However...  statistics says that it should happen once in a little
while, and it has happened in my machine :-(((

As I wrote yesterday night (at least for me here in Italy), I got a
second Apple II which was fully working. Then I started to experiment:

-- I have removed the motherboard on the new, "working" A2, connecting
it to the power supply of the "dead" machine. Ok, works. The power
supply is OK (no doubt on that, I had already checked the voltages, it
was just to be sure).

-- Following my "inner feeling" I have pulled out the 6502 on the
"working" motherboard. Power ON: no beep, nothing (I would have been
**surprised** if it HAD worked :-)) ). The video screen resembles that
of my "dead" motherboard. Uhmmm...

-- Finally I have swapped the two processors. Now the "working" machine
is "dead" and the older "dead" A2 resurrects (well, ... nearly) to life. 

-- Just to be sure and to rule out problems with contacts, oxide on the
pins, etc, I have swapped back and forth the two processors a couple of
times. No doubt, it is the 6502 which is dead.

What is strange to me now is that the screen shown by second A2, that
now houses the dead 6502, is quite different (many different characters
in random positions) from what I previously observed on the original
machine, where I had alternate rows "@"s and "!"s. 
Any idea? 
The only thing that comes to my mind is related to different
initialization of the video RAM.

Cheers
Sabino