On Tue, 16 Oct 2012 22:45:12 -0700, (Dave Platt)
wrote:

I have some EPROMs which show some short circuits between adjacent
pins. I got rid of the shorts by scraping the white sealant with a
needle and now they program and read correctly.
Should I put something to seal the chips again? What can I use?

In either case... there are quite a few "conformal coatings" that you
can use to protect PCBs and chips against moisture infiltration...
acrylics, urethanes, epoxies, silicones, etc. In a lot of situations
they are quite unnecessary.

Approximately how many ohms is the "short circuit"?

If there's a conformal coating, it always has a phosphorescent dye
mixed in to allow for inspection. Where there's no blue or green
glow, the coating needs to be touched up. Find one of the cheap UV
LED flashlights, and inspect the EPROM for the dye.
http://www.youtube.com/watch?v=38V-xLSZW74

If coated, try dipping the EPROM in some nasty solvent, such as paint
thinner, acetone, xylene, or trichlorehtylene and see if anything
appears that looks like a coating. If you want to go for broke, try
paint stripper (methylene chloride) which will surely remove any
coating. Scrape off the mess with a wire brush. Oh yeah, wear
protective gloves and do it outside so you don't breath the chemicals.

In the distant past, I had to deal with a product that was rather
static sensitive. Management didn't want to deal with a redesign, so
I stupidly suggested that we spray it with conductive anti-static
spray and seal it with acrylic spray conformal coating. I think it
was about 100 Kohms/square. The problem was that the resistivity was
not stable, and would change with coating thickness, temperature,
humidity, handling, and the position of the moon. I eventually did
the redesign. Hopefully, wherever the EPROM's originated, did not
have the same bad idea.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558