Re: MOS8520R4 - 1988 vs. 1991

On Thu, Jan 30, 2020 at 3:16 PM Mia Magnusson <mia_at_plea.se> wrote:
>
> Den Wed, 29 Jan 2020 18:28:39 +0100 skrev Gerrit Heitsch
> <gerrit_at_laosinh.s.bawue.de>:
> > On 1/29/20 6:08 PM, Francesco Messineo wrote:
> > > Btw, I have a PCB of some device (it has a midi interface, I can't
> > > tell much more about it) that happened to use
> > > MOS general purpose TTL clones (like the 7406 equivalent and others
> > > that were found on some C64 boards too).
> > > So in some cases, those chips were sold to other companies.
> >
> > Probably at the height of the TTL supply crisis when they had
> > leftover stock.
>
> It might also had been a business decision, sending out the signal that
> if other manufacturers set the price point too high Commodore would
> just produce their own chips.
>
> Btw I didn't know that they made a 7406 equivalent. Only seen the
> 74LS245 clone-ish 65245.

not only that:

https://www.c64-wiki.com/wiki/MOS_Technology_Products

look for the 77xx chips.

>
> Btw, are those that bad, or have they gotten a bad reputation due to
> other factors? The 74xx06 is one of the first things to give in if you
> insert the power supply cable in the serial port (which with some power
> supply connectors is sursprisingly easy to do) backfeeding the
> computer with all kinds of incorrect voltages. (I have a VIC 20 where
> someone must had left it in this state for an extended period as the
> case had started to melt under where the 74xx06 sits :O )

I repair a lot of CBM stuff (most of my repairs are on youtube:
https://www.youtube.com/iz8dwf )
In my repair logs the failed 77xx are approximately 1/10 of the ones
I've found installed on CBM boards.
Regular TTL 74xxx (and LS) family failure rate is less than 1/100.
Some brands are worse than others though.
Also 2114 SRAM failure is higher for MOS parts than other brands'.
Another famous chip for high failure rate is the mT4164 DRAM, 1.5/8
failure rate in my repair logs.
By the way, one of the C64 I kept in my collection suffered the power
supply into IEC port "problem", I've found it next to a trashcan :)
Problems on that board weren't only limited to the 7406.
Frank