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>