One of the Mac’s greatest strengths is its ease of use. A related, but not as
widely touted benefit is that Macs are pretty easy to troubleshoot, especially when
compared to Windows-based PCs.
First of all, because Apple designed most of the hardware that goes into Macs and Mac
clones as part of an integrated system, Mac hardware problems are much less frequent than
Windows PC-based problems. Second, Mac hardware problems are often less
complicated—loyal Mac enthusiasts will never have to worry about confusing subjects
such as IRQs and the like.
That’s not to say that Macs don’t have any problems, though, because they do.
(For more info on software-related Mac problems, see the "Mac Software Troubleshooting Tips"
article.) And when you run into hardware problems on a Mac, they can be just as
frustrating as any problem you’ll run into on a PC.
Take the First Step
As with PCs, or any electronic device for that matter, the first thing to do any time
you encounter what appears to be a hardware problem is to check the obvious stuff. Look
for loose or unconnected cables—you’d be surprised how often a quick jiggle to
the cable fixes a problem. Look at the cable connectors as well, particularly for things
like bent pins. I recently solved a modem problem by noticing that the adapter for my
PowerBook’s PC Card modem had a pin that was bent so far out of the way that I could
still connect the adapter to the modem—but of course it didn’t work. Once I bent
the stray pin back into place and reconnected the adapter, everything was fine.
If the problem is with a new PCI plug-in card, try pulling it out and then reseating it
back into the slot. The card needs to fit very tightly or it won’t work properly.
Accelerator cards or processor upgrades can also be problematic on Macs, or other MacOS
compatibles. Unfortunately, the problems here are usually due to incompatibilities between
these cards and either the MacOS or individual applications—which means there really
isn’t anything much you can do about them other than finding out if you can somehow
upgrade your accelerator or processor upgrade card.
If you've just added new RAM and either the system won't boot or won't recognize the
additional memory, either you need to pull out and re-seat the DIMMs (or SIMMs) or you may
have to try RAM made by a different manufacturer. While all RAM should work the same, the
reality is that tiny differences in design can cause a particular manufacturer's RAM to
not work in a particular Mac model (or PC, for that matter).
The Skinny on SCSI
Probably the most common Mac-related hardware problem has to do with SCSI (pronounced
"scuzzy") conflicts. Because the Mac has had a SCSI port since it’s
earliest days, SCSI peripherals have always played a big role in MacOS systems. Hard
drives, CD-ROM drives, scanners, removable drives and more are all available as SCSI
devices for Macs, both in internal and external versions (because virtually all Macs have
both internal and external SCSI connectors—even newer Macs that use IDE hard drives).
SCSI problems often manifest themselves on startup--often times your Mac won't be able
to boot because of them--but they can also show up while using a particular application or
trying to access a SCSI device (such as copying a file to an external drive, scanning in a
photo from a SCSI-based scanner, etc.)
To completely understand the issues involved, you need to know a little more about what
SCSI is and how it works. SCSI is a high-speed, bi-directional interface that allows you
to connect up to 7 different devices to a Mac. Devices of connected components are
referred to as SCSI chains and all SCSI chains begin at the SCSI controller.
On most Macs, the SCSI controller is a chip on the motherboard. Some Macs include two
of them: one for internal components and another one (which often runs at a
different—typically slower—speed) for external devices.
The controller chips support one of several varieties of SCSI: normal SCSI, Fast SCSI
(sometimes called SCSI-2), Wide SCSI, Fast and Wide SCSI, Ultra SCSI (or SCSI-3) and Ultra
Wide SCSI to name a few. These various flavors of SCSI differ primarily in how fast
they’re capable of sending data down the line, although Ultra SCSI also ups the
maximum number of supported devices on a single SCSI chain from 7 to 15.
Regardless of the type of SCSI capability that the controller supports, however, you
can attach any SCSI device to any SCSI chain because all SCSI components can work together
without any problem. However, if you attach a fast device capable of supporting the 40
MB/second transfer rates of Ultra Wide SCSI to a Fast SCSI controller (the kind typically
found on today’s Macs, which offers a maximum transfer rate of 10 MB/sec), the
attached device will not be able to operate at its peak performance. This is because the
maximum speed of any device on the chain is determined by the SCSI controller, not by any
particular device’s capabilities. (This is why some people who need maximum
performance opt to purchase plug-in SCSI controller cards for their Macs, even though they
already have a SCSI port.)
For a chain of SCSI devices to work properly it needs to be terminated at each end. If
it’s not, then all kinds of strange problems can result. And in fact, many SCSI
problems (on both Macs and PCs) are due to improper termination. Since all SCSI chains
begin with the controller, it has its own terminator, which is always on. Individual SCSI
devices also come with terminators—on some devices it comes in the form of a short,
adapter-like plug that attaches to one of a SCSI device’s SCSI ports. (Most devices
include two SCSI connectors so that they can be included in the middle of a chain,
although some devices have only one SCSI connector, which means they always have to be at
the end of a SCSI chain.)
On other devices, including all internal SCSI drives, there’s a small jumper
switch on the back panel that you can turn on or off as needed. The latest development is
automatic termination, where a device can tell whether or not it’s the last one in
the chain and then turn the termination on or off as necessary. (Even these type of
devices offer a manual switch in case you need to override their automatic settings,
however.)
All devices in the middle of a SCSI chain must have termination turned off and all
devices at the end of a SCSI chain must have termination turned on. If you’ve got
multiple SCSI chains, such as one internal and one external, you need to terminate the
device at the end of each chain. If you don’t, the Mac may be unable to boot, or may
crash randomly. Sometimes an improperly terminated chain will work for a while and then
start to blow up, so if you’re Mac suddenly starts working strangely, check your SCSI
chains.
Even if all your termination is set properly you may still run into problems that are
related to the SCSI devices connected to your Mac. The reason for this is that the
physical connections between various SCSI devices can be very temperamental—cheap
SCSI cables are a notorious source of strange problems, for example. If you continue to
have strange problems that you believe are due to your SCSI chain, invest in some
high-quality (i.e., expensive) cables and see if that solves them. You should also try
switching your cables around—as strange as it may seem, sometimes reversing a cable
so that the portion that was originally connected to the Mac is now connected to the
attached device and vice versa can make a difference.
If that still doesn’t work, I would consider investing in an active terminator,
which is essentially a fancier terminator that is more effective at blocking signals that
can bounce around the SCSI chain and cause problems (which is what terminators basically
do). To help out with your Mac SCSI troubleshooting, I also suggest you download SCSI
Probe, which is popular utility for finding SCSI problems on the Mac.
One final trick to consider if it's your internal SCSI hard drive causing the problem
is to boot from a MacOS CD. Most Macs can boot from a CD-ROM with a System Folder by
holding down the C key when you start up the machine. Once you've done so you can use Disk
First Aid (which should be somewhere on the MacOS CD) to check for disk errors and/or
update your hard disk drivers.
Zap, Zap, Zap
If your Mac serial ports seem to be causing problems—for example, if you
can’t communicate with an external modem, printer or other device attached to your
Printer or Modem ports, you’re a prime candidate for resetting your Mac’s
Parameter RAM, commonly called PRAM. A Mac’s PRAM is roughly equivalent to a
PC’s CMOS—it’s a small amount of battery-backed memory that stores various
settings for your computer, such as the time, etc. On the Mac, it also has settings that
can effect communications with devices attached to your serial ports. The process of
resetting the PRAM is called "zapping" the PRAM.
To zap the PRAM on your Mac you need to restart your Mac and then quickly hold down
four different keys simultaneously: Command-Option-P-R. If you’ve done it
successfully you’ll hear a quick chime (and if you keep holding them down a bit
you’ll hear several chimes), and then your Mac will reboot. Most Mac people recommend
that you let it ring a few times to completely flush out the settings stored in the
PRAM. Often times zapping the PRAM can clear up a variety of different hardware-based Mac
problems.
If that still doesn't work, you may have a software-related problem (many times they're
hard to distinguish). For more info on Mac software problems, check out the "Mac Software Troubleshooting Tips" article.
Finale
Most people buy Macs for their ease of use and so get frustrated if they run into any
kinds of problems. Thankfully, paying the "Mac premium" generally does give you
a computer that causes a lot less problems than Windows equivalents, but not always. If
you follow some of these steps when you do come across a Mac hardware problem, you should
soon be able to productively smile back at your computer’s happy Mac face.
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