Date: Tue, 4 May 1993 03:49:58 -0700 (PDT) 
From: Guy Kuo <guykuo@u.washington.edu>
Subject: IIsi-clock-mod-poll.txt 

Report on poll of users who have upgraded their IIsi clock oscillators for
higher speed. Suggest placement in reports folder.

------------------------------
This poll was conducted to help users decide whether or not to alter their
IIsi clock oscillator. I have attempted to gather as many case histories as
possible to find some estimate of success and risk. The number of replies
probably shows how rare this modification is but give the impression that
success rates may be higher than the previous 80% estimate. 25 of 25
machines were able to run at 25 mhz when no add on boards were present.
This is not a scientific survey but it is the best we have to work with.

Thanks to all who contributed to this poll. 


Issues:

        Speed) 25 mhz to 27.5 mhz appears to be the norm for machines
                without add on cards. All reported machines were able to
                use 25 mhz as long as no add on cards were present. Several
                Apple cards were in use. No machine with the Nubus adapter
                was able to go faster than 25 mhz. One wasn't even able to
                achieve 25 mhz with the Nubus adapter in place
        
                At speeds >= 30 mhz, the startup sound may crackle
                and hi density floppy disk problems have been reported.
                
                Note: Unless specifically listed below, machines were not
                        tested with a higher speed clock to failure. Hence,
                        the 25 mhz operational machines may well work at
                        higher speeds.
                        
        Damage) One user reported pulling out the plating of one pad. This
                was repaired and the machine is operational. One other
                reported pulling the pin out of the original clock
                oscillator during desoldering. There is one second hand
                report of a user putting a gash in the motherboard with a
                slipped soldering iron.
                
                No reports of static discharge damage.
                
                No reports of high speed operation causing damage.
                
                Then again, I also don't have any reports from users of
                defective parachutes.
                
        Add on boards) Compatibility appears to be a problem with Apple
                Nubus Adapters. Several other add on boards have been used
                with success. See case histories
                
        Heat Sinks) Virtually all modified machines had a heat sink
                installed. These were often the TO-220 style power 
                transistor type. Some used epoxy. Some used a dab of heat
                sink compound with a dab of cyanoacrylate glue. There was
                also use of a clamp with a bolt through the hole in the
                motherboard.

                James MacPhail <jmacphai@cue.bc.ca> is gathering evidence
                which indicates a heatsink is advisable
                
                
                
Case Histories:        

All speeds are the effective CPU speed (1/2 of clock oscillator). All reported CPU versions were 20 mhz.

1)  27.5 mhz operational. Ran for 10 minutes at 31 mhz before crashing.
    No FPU or other add on card
    Heatsinked CPU only
    On 24 hours/day
    No damage during installation
   
2)  27.5 mhz operational without Apple Nubus adapter. 25 mhz top speed with
        Apple Nubus card installed
    Heatsinked CPU only
    On 24 hours/day
    No floppy problems
    No damage during installation
   
3)  27.5 mhz operational. Unable to boot at 31 mhz
    Heatsinked CPU only
    No floppy problems
    No damage during installation
   
4)  25 mhz operational
    Works with the following two configurations
        
                a)      Realtech FPU adaptor card
                        Realtech Cache card
                        SuperMac 8*24 PDQsi
                
                b)      SuperMac FPU adaptor card
                        SuperMac Video Spigot
                        SuperMac 8*24 PDQsi
                        
5)  33 mhz operational
    Fuzzy startup sound
    Problems with hi density disks

6)  33 mhz operational
    Fuzzy startup sound
    Heat sink on CPU and chip to right of CPU
        
7)  25 mhz operational. Occasional crash at 33 mhz

8)  25 mhz operational.
    Using FPU rated at 16 mhz without difficulty
        
9)  25 mhz operational.
    PDS adapter with a Spectrum 24PDQsi graphics card and a 
    VideoSpigot, a 20MHz FPU
    Heat sink on CPU
        
10) 25 mhz operational. 33 mhz failed after several hours.

11) 25 mhz operational
    5/80+quicksilver/fpu(only upgrade)
         
12) 25 mhz operational. Tried 33 mhz - system won't start. 
    Heat sink on CPU
    Configured with
         RealTech FPU/adapter card
         Supermac 8*24 PDQsi
         Realtech cache.
    CPU on continuously - no problems.
    Floppy works fine at 1.4MB @ 25 mhz
        
13) 25 mhz operational
    Heat sink on CPU
        
14) 25 mhz operational
    Heat sink on CPU
        
15) 25 mhz operational
    Heat sink on CPU
        
16) 25 mhz operational
    Heat sink on CPU
        
17) 25 mhz operational
    Heat sink on CPU
    On 17-19 hours per day
        
18) 25 mhz operational
    Heat sink on CPU + cooling fan
    No floppy problems at 25 mhz
        
19) 20 mhz operational. Bombed soon after startup at 25 mhz with Nubus
      Adapter
    20 mhz rated CPU
    RAM 70 ns in slots, 80 on motherboard
        
20) 25 mhz operational
    Heat sink added to CPU later. No damage while unheatsinked.
    Apple Nubus adapter with FPU installed.
        
21) 25 mhz operational
    Heat sink on CPU
        
22) 25 mhz operational
    Heat sink on CPU
        
23) 25 mhz operational
    Heat sink on CPU
        
24) 25 mhz operational
    Heat sink on CPU

25) 30 mhz operational 5/240 with Nubus adaptor
    Ran 1 week at 31 mhz
    Heat sink on CPU
    Sound does not crackle at 31 mhz
    Floppy drive recognizes HD disks at 30 mhz but will not read properly
    Add on RAM is 70 ns


        
Guy Kuo <guykuo@u.washington.edu>