2 Aug
2014
2 Aug
'14
1:50 p.m.
On 2014 Aug 2, at 8:38 AM, Ian McLaughlin wrote:
Does anyone have an old National Semiconductor memory
data book
lying around? I have found the problem with my second 32k memory
board - 3 bad DRAM chips. This board is populated with MM5298N-3B
chips. I can't find an online data sheet that talks about the speed
grade (I'm assuming that's what the 3 is referring to). The manual
for the board ( http://www.hartetechnologies.com/manuals/Northstar/
NorthStar%2032k%20RAM-32-A.pdf ) says that the RAM is 200ns access
time. I can find a source for MM5298N-4B chips, but I don't know if
the 4B is still fast enough. I'll replace the entire bank of 9
chips at the same time so that they are matched.
The datasheet here shows 3 speed grades on page 3:
http://www.alldatasheet.com/datasheet-pdf/pdf/148601/NSC/MM5298.html
-2A -2B: 150ns
-3A -3B: 200nS
-4A -4B: 250nS
Going by the timing relationships on page 18 of the board manual vs.
the datasheet timing specs, it looks like the -4 will be too slow.
(IMO, I wouldn't worry about needing to replace the whole bank.)
Coincidentally, just yesterday I was repairing a Northstar 16K DRAM
board, nearly identical design but with 4K chips. Shorted tantalum,
failed regulator, and 2 bad TI 4027 chips (no spares in my stock
bins, darn it).