5 Oct
2007
5 Oct
'07
12:16 p.m.
Date: Wed, 3 Oct 2007 09:28:05 -0700> To: cctalk at
classiccmp.org; cctech at classiccmp.org> From: healyzh at aracnet.com> CC: >
Subject: Re: EPROM Death? / EPROMS> > At 9:31 PM -0400 10/2/07, Allison wrote:>
> > From: "Zane H. Healy" <healyzh at aracnet.com>> > >>
>>How do you tell an over-erased EPROM?> >>> >>I finally have my
programmer and eraser, and just tried erasing 6> > >EPROM's. Four erased just
fine, and two are showing weird patterns> > >of alternating blocks of 04/06 and
14/16.> > >> >I've seen that when the quartz window isn't really
clean and the> >UV hasn't quite done the full job. I have found some vendors>
>eproms need a little more time to cook.> >> >Ove 26 years I think I've
only seen one that really had a stuck> >bit and that was a blown output pin.>
> The two EPROM's in question are 27128's of different manufacturers. > The
strange thing is both have the same pattern in them (I read them > in when checking). I
did manage at the same time to erase a 27C128, > 2 different 27C256's, and a 27256.
Rather irritating as I'd prefer > to use either 27128's or 27C128's for the
next step. Hopefully > either these two really are good, or the other two I have, and
still > need to erase, are good. I won't be able to mess with this more > until
at least tonight.> Hi
As Phil mentions, people have left EPROMs under UV for
days.
Normally the only issue is that they may not hold data as long.
As I stated before, your problem sounds just like
bad contact to the pins. Many EPROM sockets only connect on
the edges of the pins. The pins can look clean while still
having any number of oxided and such on the edges of the
pins.
Clean the pin sides before giving up. Use some fine 220 sand
paper and some small pliers to apply some force to the sand
paper.
Remember that the sides of the pins may not be plated and
are often exposed base material. This is most often brass
or even some iron mixtures. It doesn't take much corrosion
to be a problem in a ZIF type socket.
Dwight
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