[vcf-midatlantic] Testing 4164/41256 RAM Chips
hjohnson at retrotechnology.info
Fri Sep 15 14:49:13 EDT 2017
Responding to various suggestions for old DIP-chip RAM testing.
cheap EPROM programmers that test things like TTL or RAM, are not likely
to be better than go / nogo. THey won't test at anything like access
speed. Commercial grade RAM testers are likely better, but few have those.
Vintage computer designs for DRAM were not always very good, and many of
them aged poorly. (Changes to the other components make the DRAMs work
marginally.) What chips may work in one brand/model, may not work in
another. And frankly, prices for old 16K and 64K and 256K chips (IBM PC
class) are fairly cheap - buying them is simpler than extracting and
testing. Now, if someone needs an exact brand/model/datecode of DRAM
chip, then more effort is warranted.
Otherwise, there's not much incentive to work hard to test these chips.
One puts them in the application hardware and runs such tests as they
can. Some of these old circuits not only need component repairs, they
need in-field circuit changes. This is hard work that few do. Also:
specific brand model owners probably have known-fixes and specific
suggestions about DRAM selection. But for some vintage systems, one can
choose static RAM and have better luck than with DRAM.
Herbert R. Johnson, New Jersey in the USA
http://www.retrotechnology.com OR .net
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