Tektronix 4097 GPIB 8" Floppy Drive

[Tony Duell]

> With the service manual saying that that the FAULT light being on is
> most likely indicating a RAM problem, I started looking at the datasheet
> for the MK4027 chips used in the 4907.  I don't have any of these (or
> equivalents) on hand, but I then looked at the datasheet for the MK4116
> (a 16K x 1 DRAM), which, I happen to have a bunch of.  The only
> difference between the two devices is that the MK4116 replaces Pin 13
> (~CS) on the MK4027 with A6.  All of the other pinouts are identical,
> and the voltages and general timing specifications are the same between
> the two chips.  What I'm wondering is if I could just pull all of the
> MK4027's and replace them with MK4116's.  In the schematic for the RAM
> section of the 4907 controller shows the ~CS pin on all of the MK4027's
> is wired to ground.  This would have the effect, with a 4116 plugged in
> place of the 4027, of forcing the A6 address line 0 at all times, which,
> if my brain is working properly (there are days when I wonder), should
> not have any effect on the 4116's ability to serve as a replacement for
> the 4027s.

The problem comes when the CS/ pin of the 4027 is used for something. In 
that case, if you replace the 4027s with 4116s, you are likely to end up 
with a bus contention, since the 4116s will probably not be disabled at 
the right time.

But if CS/ is grounded, the selection must be done in some other way 
(gating the CAS/ line is the most obvious). In which case there is no 
problem. 

It should work fine.

-tony