Remove _ for valid address wrote:

In article , Michael A. Terrell wrote:


Really? Then explain the 4164 chips of various brands marked 300
that tested to 150 or better on my RAM tester. I repaired a LOT of
Commodore 64 computers, and bad or slow memory was one of the biggest
failures. I salvaged thousands of used 4164 and 41256 chips from Unisys
mainframe memory boards. All that were still good (over 99%) tested at
least one level faster than they were marked. They told me that they
bought millions of RAM chips, speed tested them, and then sold the
slower culls to the IBM clone makers and on the spot market.

Did you test them at worst case conditions? The manufacturer ensures
they meet spec at all legal conditions, the slowest conditions would
typically be low voltage (-10%?) and high temperature (often 70degC,
maybe even 100degC?) so if you're testing them at room temp and nominal
voltage they'll run considerably faster.

Mike.


The RAM tester checked the memory at three different voltages,
(VCC-10% VCC and VCC+10%) and had a calibrated, adjustable clock to set
the test speed. Most of my testing was done at either room temperature
of 85 to 90 degree Fahrenheit, or at full operating temperature when
socketed chips were pulled from a working motherboard. I was repairing
hundreds of Commodore C64 computers, and early IBM clones with 4164 and
41256 RAM. I know there was fancier test equipment available, but I
could test or verify bad RAM in seconds. Some that were marked 300
would test at under 100, while others in same the batch tested close to
the guaranteed 300 under the same test conditions.



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