Re: 7712 info

On 6/18/20 10:00 PM, Francesco Messineo wrote:
> On Thu, Jun 18, 2020 at 9:49 PM Gerrit Heitsch
> <gerrit_at_laosinh.s.bawue.de> wrote:
>>
> 
>>
>> Yes, but often, if you have a dead C64 with a lot of 77xx chips on it
>> it's one of those that is the problem (unless it's the PLA, but that is
>> also known as '7700-xx' or '8700-xx').
> 
> I've repaired dozens of C64 :)
> Once I've found a C64 that had almost all 77xx logic chips and one by
> one I had to change them all to revive it.
> I don't desolder parts before making sure they are really bad usually.
> I've never said they're reliable, but they aren't either all failed by
> now for sure.
> 
> What is really "disturbing" in the MOS reliability issue is that it
> appears to  depend on the part number too.
> Either some parts were made in different farms, so the less reliable
> farms were producing the less reliable part numbers
> or it was heat-related maybe (like the hotter parts failing more often)...
> I tend to believe it was a "farm" issue.

As far as I know, MOS made all their chips in their one factory but then 
sent a lot of wafers out for packaging to places all over the world. 
During packaging the seeds for an early death might have been sowed. One 
exception might be ROMs, even if they have the MOS logo, they aren't 
necessarily made by MOS, but mask ROMs can be made by about every 
semiconductor maker.

  Gerrit