[sdiy] EPROM curiosity

[rburnett at richieburnett.co.uk]

There's lots of ways that memories can fail to meet their performance 
spec.  For example they could fail to read or write reliably at the 
extremes of supply voltage or temperature, often with just a few cells 
failing to read/write at the most demanding extremes of the timing spec. 
  These are meant to get screened out during wafer-level testing, and get 
packaged and marked as lower-spec (reduced temperature range, or longer 
read/write latency) devices, or scrapped altogether depending on the 
level of the defects.  (For EEPROM, flash and RAM there is also write 
endurance.  I've seen dodgy SRAM chips fail read-back testing from 
faulty cells at low temperature and voltage after only a few tens of 
thousands of R/W cycles!)

So if you may have done a production run with questionable quality 
parts, the best thing to do is some soak testing at the limits of supply 
voltage and ambient temperature.  In my experience this is very 
effective at weeding out potential field failures, and minimising 
recall.  (As I'm sure you know, this type of temperature cycling is also 
very effective at revealing dry joints and poor crystal oscillator 
quality too!)

-Richie,

On 2014-05-08 13:47, Steve Lenham wrote:
> I use a fair few EPROMs for firmware upgrades in synths and effects
> units. From time to time (and with my eyes fully open) I have
> purchased "new" EPROMs from Chinese eBay sellers, especially
> smaller-capacity parts (2716, 2732, etc). What I receive are
> sparkly-new-looking devices which - so far at least - program up and
> work just fine.
> 
> However, I wasn't born yesterday and know that the chances of them
> really being new parts from the stated manufacturer are pretty slim.
> My question is this: has anyone got any insight into what these
> devices might really be?
> 
> A frequent answer is "failed devices from the factory bin", but I
> didn't think anyone had been making 2716s for some time.
> Larger-capacity devices packaged with a different pinout? If that is
> the case, they are performing a useful service! Recycled used parts?
> If so, I would like the same guys to come and clean my workshop
> because they are pristine.
> 
> Or am I being too cynical? Maybe they are what they claim to be!
> 
> Please note: I'm just curious about the technicalities here and don't
> need to be warned off buying from Chinese eBay sellers...we've all
> read the horror stories but a bit of risk can be fun :-)
> 
> Anyhow, I don't need Chinese 2716s now that I've discovered the
> Ukrainian clones that were still in production well into the '90s...
> 
> Cheers,
> 
> Steve L.
> Benden Sound Technology
> 
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