Re: Another Zip story...

[o9938156@wsuaix.csc.wsu.edu (mark lyon)]

bazyar@netcom.com (Jawaid Bazyar) writes:
: 
:   My guess is actually power distribution problems and power/ground
: noise caused by the Zip's 2-layer design. I have not yet proven this,
: however.
: 
:   Knowing that the Zip likes "low-power" SRAMs (but not standard SRAMs)
: leads me to guess that it's a problem with noise on the power pins of
: various parts on the board (caused by the SRAMs switching, of course).
: Whoever made the decision to save a couple bucks on the Zip at the
: cost of high-speed reliability ought to be shot. 4-layer does NOT
: cost that much.
: 
Weren't some early Zip's 4-layer?  If so, why was the design
scrapped?

: >So, I wrapped the Zip in several layers of aluminum foil
: >(the thicker, the better) and connected the foil electrically
: >to the metal case of the GS.  
: 
:   I'm not sure how effective a capacitor this is; I would guess
: not very much at all, so this 'solution' may be only partially
: related (or not at all) to my guess.
: 
Well, the sheilding isn't meant to be a capacitor, it is meant to 
prevent RF noise from other components in the GS from corrupting
the cache ram.  The shield probably does increase capacitance to
ground somewhat, but like you said, probably not very much.  If
the noise source is on the board itself, than the shield around
the board would be about as effective as a bucket of yak spit :)
Obviously, the shield is doing _something_, because I can't boot
at all w/o it, and the GS will run for a little while at least,
with it.

:   I recommend soldering fairly big caps (1uF perhaps?) onto the power/ground 
: pins of all the SRAM sockets, and standard 0.1uF caps onto the 
: TTL parts.  You also might try running heavy-gauge wire from the
: power pin on the GS slot connector to the SRAMs (same with the ground

Thanks for the tips, I'll try them.  Hey, capacitors are cheaper
than SRAM's!  Are the power/ground pins on the SRAM's the
somewhat usual pins 1&28?  Are the TTL parts you refer to
the 74Fxx chips?  And, finally, what are the power/ground
pins on the slot connector?  Thanks!

Mark.  

:   All in all, the Zip's board layout is rather unimpressive.
: 
: -- 
:  Jawaid Bazyar              |   Like UNIX? Like your Apple IIGS? Then ask
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