Re: ZipGS only stable with 32K - why?

[wbaguhn@nyx10.cs.du.edu (Will Baguhn)]

In article <20JUL199604394633@vax2.concordia.ca>,
Mitchell Spector <spec@vax2.concordia.ca> wrote:
>   About a month ago, I received a pre-upgraded 15 MHz/64k cache ZipGS
>board. The original owner claimed it was perfectly stable with the
>modifications he made and the type of static RAM chips picked. It had
>run on his ROM 3 for well over a year with a stock powersupply and a
>few cards. However, when I installed it in my system (also a ROM 3 with 
>stock powersupply) I began to experience lock-ups and freezes.
>
>   I decided a weak/overloaded powersupply might be the cause, so I
>purchased one of Stephen Buggie's 150W PC supplies. Unfortunately it
>made little or no difference, the ZipGS would continue to lock-up!
>Usually it runs perfectly stable for several minutes, then suddenly
>a lock-up occurs, then yet another and so on, until finally it gets so 
>bad clicking on a Finder icon will cause an instant lock-up (mouse pointer 
>moves but background frozen -- yellow/green LED on card at this point gets 
>very bright and stays on). I tried swapping in another oscillator, slowing
>the board down to 12.5 MHz, though the same problem still occurred. 
>
>   The only solution I found, is flipping the card's DIP switches so
>it's configured for 32K cache (effectively, this tells the card to
>ignore the upper 32K of cache). My question is: _why_ on earth does
>the board run with 32K cache but not 64K cache? I doubt the chips are
>faulty, I've swapped the TAG chips around, still no difference. They're
>also the correct speed (TAG = 15ns, DATA = 45ns) and _did_ function in
>a similar IIgs setup without causing lock-ups. At present I'm running
>the board as a 15/32, but I'd like suggestions on how to get it working
>as a 15/64. Note 15 MHz works absolutely fine, it's the cache that is the
>sole problem (I'm running stable now with it as a 15/32).
>
>My system consists of (listing everything, just incase :)
>
>ROM 3 CPU, Buggie 150W PC supply, System Saver IIgs (cooling insides), 
>Apple 3.5, Apple 5.25, Apple SuperDrive, TMS Shadow HD w/730MB Quantum 
>Lightning, USR Sportster 14.4k, Mach III joystick, Quickie scanner, 
>standard IIgs keyboard and mouse. Also unshielded Bose speakers,
>AppleColor RGB and ImageWriter II, but I doubt the latter could
>be linked to any problem.
>
>[Slots]
>1: 
>2: Audio Animator (currently MDIdeas cards plugged in)
>3: ZipGS 15/64
>4: ComputerEyes GS
>5: Quickie interface
>6: Apple II 3.5 Controller Card
>7: RamFAST rev D, 1MB
>
>Mem Exp: Sequential Systems RAM-GS 4MB
>
>Mitchell Spector
>spec@vax2.concordia.ca

Did you try switching the DATA chips as well, and seeing if that caused
the system to crash?  If it crashes when the chips are switched, it
may just be bad SRAM.  Otherwise... have you looked to see if the
split cache mod has been installed on the Zip?  If it has, setting the
cache for 64k should be enough to crash it. (Split cache Zips should be
set for 1/2 of the "actual" cache size.  To see if the mod is installed,
look at positions J6 and J7 on the Zip... if there are wires soldered
in between pins 1 and 3, the mod is installed.)

-- 
                                      --- Rev. SPQR (wbaguhn@nyx.net)