User`s guide

A good indicator of power problems is a noticeable drop in voltage on the
+5V line as measured on the motherboard. Instead of the 4.9V - 5.0V typical for
a light load, it will be 4.7V or lower.
Measurements and experiments with standard IIgs power supplies indicate
that the actual DC voltage drop through the 18 gauge +5V and Ground leads is
only (approximately) a total of 0.04V at 3Amps, which is what a moderately
"loaded" IIgs system will draw. The explanation for getting a drop of 0.2V -
0.4V or greater appears to be power supply regulation error. Some standard (and
"heavy duty") Apple II power supplies with 18 gauge leads will hold at-
motherboard voltage to around 4.9V at 3-4 Amps and som
e won't.
It is easy to see that a system designed to work at 5 Volts will eventually
begin to malfunction as the available voltage drops by half a volt or more. In
fact, any actual computer system would be likely to experience crashes long
before the average, measured at-motherboard voltage got down to 4.5 Volts.
A voltmeter reading at the motherboard does not show instantaneous spike or
"noise" voltages. Each time a circuit switches, there is a change in current
drain. Quite a few circuits are switched with each main system clock transition;
so, the change in current can be substantial at 1 x and 2 x main clock
frequency. Other events, like turning ON a disk drive, can also produce brief up
or down shifts in current drain. Either way, you have brief changes in voltage
across the power supply and its leads.
The brief voltage changes are called "spikes" because they are VERY brief.
The larger the current shift and the greater the effective resistance of the
power supply plus its leads, the higher the spike voltage generated. Since these
spikes are in series with the circuits connected to the PS and since they are
difficult to eliminate via bypass capacitors, they propagate throughout the
system.
Even worse, as current draw increases and spike voltage increases, at-
motherboard supply voltage decreases. So, you have a 'double whammy': the
lowered supply voltage reduces IC noise immunity just when you need it most.
At some point, noise spikes appear which cause latches, memory IC's, etc.
to switch state. If the latch is on a RAMfast, you may get a disk read error. If
a memory chip is affected, data will be corrupted, program instructions may
change, ....; in short, your computer is likely to malfunction.
All of which is bad enough; but, there may be another negative affect when
noticeable system noise appears 'across' the power supply. How many csa2 posts
complain about GS power supplies that crater "for no reason" after just a couple
months? How many users seem to be on eternal quests for a solution to PS woes?
Reducing the noise may significantly extend the life of your Apple II power
supply.
Power supplies with noticeable regulation error often benefit greatly from
heavier leads, especially for +5V and Ground. Reducing the actual drop through
the lines reduces the resulting error; and, at-motherboard voltage is back to
4.8V or better under high loads. The heavier leads also reduce noise.
Whether or not tighter regulating power supplies benefit significantly from
swapping in heavier leads is an open question. At high switching frequencies the
power supply's leads will have a higher effective resistance and the spike