[vcf-midatlantic] Good source for eproms?

[chrisjpf33 at gmail.com]

On May 25, 2016, at 7:14 AM, Jason Perkins via vcf-midatlantic <vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:

The EPROM on the drive now doesn't have a window. I thought that means
it's only one time programmable?

Dave, I'll drop you a line off-list. Thanks for the offer!

-J

On Tue, May 24, 2016 at 11:54 PM, Dave McGuire via vcf-midatlantic
<vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
> 
>  Yes.  The problem with EPROMs forgetting their contents is charge
> leakage from the floating gates, not chip failure.
> 
>  I have a metric assload of EPROMs (literally thousands) of nearly
> every type, especially the really common ones like 2764s, if anyone
> needs them.
> 
>              -Dave
> 
>> On 05/24/2016 11:52 PM, Ian Primus via vcf-midatlantic wrote:
>> Even if an EPROM has gotten corrupted, the chip itself should still be
>> fine. Just erase and reprogram. I've yet to have a problem with doing
>> this, it's quite rare to have a dead EPROM.
>> 
>> Almost every EPROM I have has been scavenged from some sort of junk
>> board or another. 2764's and 2732's are quite common, should not be
>> hard to find.
>> 
>> -Ian
>> 
>> On Tue, May 24, 2016 at 11:22 PM, Jason Perkins via vcf-midatlantic
>> <vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
>>> I'm trying to get a Plus HardCard going again. Like many the ROM has
>>> forgotten some of its bits so I want to try installing a freshly
>>> flashed one.
>>> 
>>> What's a good source for 7264s? Is it worth trying to get used ones on
>>> eBay? While I'm at it I'd like to track down a 2732 for an Apple
>>> ProFile formatting rom.
>>> 
>>> Thanks,
>>> 
>>> --
>>> Jason Perkins
> 
> 
> --
> Dave McGuire, AK4HZ
> New Kensington, PA



-- 
Jason Perkins
313 355 0085


--------------

I have been told by an electronics engineer that many PROMs without windows are structurally/electrically the same as UVEPROMs but just don't have windows. This is done for manufacturing cost savings, apparently the window is an expensive feature (I think they are Quartz). If a manufacturer just needs to program once and not erase, they use windowless ICs. A blank/corrupt one might have "failed" (gotten erased but still functional like Ian said) because of some long term radiation exposure (possibly just background radiation), and then might be able to be reprogrammed. Whether or not it is worth the trouble is another question.

Another type of ROM is "masked" meaning that the data/program is etched into the silicon in the chip manufacturing process and is permanent. These offer a further cost savings to manufacturers who are doing large enough volume. I suspect that this type is is less common in older/low volume models.

Just some ROM background that I picked up over the years, I hope it was helpful or interesting.

Chris