CENT.MBECK%MIT-OZ@MIT-MC.ARPA (04/28/84)
From: Mark Becker <CENT.MBECK%MIT-OZ@MIT-MC.ARPA>
<Why doesn't someone fix this bug?>
This is for owners of U.S. Micro's or Delta Products 64k dynamic
RAM cards - You might want to check the installation of C6, a 10-to-47
uF capacitor located just to the left of where U2 and U4 butt together.
On some boards, the silk-screening is backwards! And the capacitor
may be installed backwards as well.
Typically this capacitor, after a period of time, will turn into
a resistor and load down the -5V going to the memory chips. The voltage
on the card I have reached -4V, at which point programs started crashing.
I replaced it - local Radio Shack had it on the shelf. Went and
checked three Delta boards and found they had the same problem.
Other than that, I've found the hardware to be pretty solid - no
other problems in two plus years of operation.
Mark Becker
-------towson@AMSAA.ARPA (04/28/84)
From: David Towson (CSD) <towson@AMSAA.ARPA> Added note: The problem described by Mark may be VERY SERIOUS if the board uses 4116 type DRAMS. (I am not familiar with the board.) If this is the case, and if the capacitor mentioned degrades enough to cause loss of the -5V supply, the result will be immediate and catastrophic failure of ALL of the dynamic RAM chips. This is why the power supplies for 4116 RAMs must be properly sequenced so that the -5V comes up first and goes down last. If the board in question does not use 4116's, perhaps someone else can comment about whether the same vulnerability exists. Dave towson@amsaa.arpa