overexposed CMOS EPROM

[orange]

well I've done it, I apparently overexposed the EPROM (27c400) by UV
lamp. (now I know there is such thing)

is there any way to repair it or should I just throw it away?

I'm using Willem programmer ver3 with 12V power supply.

 

[Eeyore]

well I've done it, I apparently overexposed the EPROM (27c400) by UV
lamp. (now I know there is such thing)

How long did you give it ?

Graham

 

[orange]

How long did you give it ?

Graham

I think about 4(min) (the scale is not labeled it goes from 1 to 10).
but I have exposed it twice in succession. the window was dirty and I
wasn't aware of the danger.

 

[Eeyore]

I think about 4(min) (the scale is not labeled it goes from 1 to 10).
but I have exposed it twice in succession. the window was dirty and I
wasn't aware of the danger.

8 mins isn't going to break it by miles. I bet it's barely erased it.

Does it blank check ok ?

I used 30 mins as a typical erasure time. If in doubt an hour won't hurt.

Graham

p.s. if you can find a suitable programmer (see ebay) flash is SO much
better.

 

[orange]

8 mins isn't going to break it by miles. I bet it's barely erased it.

Does it blank check ok ?

well that is the problem, its ALWAYS blank, full of FFFFFF..
it doesn't even start programming..

BTW, I've got another EPROM that programs ok, but fails to verify.
strange thing is that when I read it and save it to file, that file is
the same as original, no errors. But willem still fails to verify it..

I used 30 mins as a typical erasure time. If in doubt an hour won't hurt.

they say here to increase it every minute:
http://wiki.xtronics.com/index.php/How_EPROMS_Work#Erasing_an_EPROM

 

[Eeyore]

well that is the problem, its ALWAYS blank, full of FFFFFF..
it doesn't even start programming..

Is the programmer reading it right ?

BTW, I've got another EPROM that programs ok, but fails to verify.
strange thing is that when I read it and save it to file, that file is
the same as original, no errors. But willem still fails to verify it..

Home built Willem ? I've only ever used commercial programmers and had no
problems. Sometimes an Eprom will go 'bad' (rarely). Chuck it.

they say here to increase it every minute:
http://wiki.xtronics.com/index.php/How_EPROMS_Work#Erasing_an_EPROM

Not an especially useful site. Try a manufacturer's app note if you can still
find one.


Graham

 

[gcd]

fom the replies - sounds more like you may have a flakey programmer, or you
tried to program it with the wrong algorithm and put 21v on a 12.5v
programming line.

Greg

 

[Eeyore]

fom the replies - sounds more like you may have a flakey programmer, or you
tried to program it with the wrong algorithm and put 21v on a 12.5v
programming line.

Oh yes, that'll kill it nicely. Early 12V Eproms only had the voltage printed
on the package rather than a different part number.

Graham

 

[orange]

Oh yes, that'll kill it nicely. Early 12V Eproms only had the voltage printed
on the package rather than a different part number.

Graham

but, the thing is, I managed to program two other chips with same
setup and they verified OK, and also work fine.
the only difference is that those 'good' eproms are 120ns and the bad
ones are 150ns.
they were all bought second hand, and only god knows how many times
rewritten.

all chips can be read with no problem.
yes, the willem is home built, but looks pro..

 

[Eeyore]

but, the thing is, I managed to program two other chips with same
setup and they verified OK, and also work fine.
the only difference is that those 'good' eproms are 120ns and the bad
ones are 150ns.
they were all bought second hand, and only god knows how many times
rewritten.

all chips can be read with no problem.
yes, the willem is home built, but looks pro..

Did the 150ns Eproms EVER work ? Either in the programmer or target system ?

Graham

 

[neon]

well I've done it, I apparently overexposed the EPROM (27c400) by UV
lamp. (now I know there is such thing)

is there any way to repair it or should I just throw it away?

I'm using Willem programmer ver3 with 12V power supply.

WHAT DO YOU MEAN OVEREXPOSED . the only thing that can happen you got the chip very hot. the idea still remain that you have ereased the chip. replace what for reprogramm it.