Busman's Holiday
Illustrated Power Mac 7500 Teardown
by Steve Wood
July 23, 2001

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Dandy Composite Digital PhotoI intended just to photograph the "feet" of my Power Mac 7500 for the column Great Classroom Computer Buys: When the Worst Can Turn Out to be the Best. After making a dandy composite digital photo of the feet, I made the "mistake" of opening the case, grounding myself out, and swiping a finger across the motherboard. Arrrh!

I was absolutely, positively certain -- almost -- that I'd cleaned the case when I replaced the chip fan on the 7500's Orange Micro PC card. This practice usually includes a somewhat thorough, yet gentle brushing with a camelshair paint brush that I keep hidden in my computer tool bag from all prospective painters. It has either been very dusty at school this year, or my memory is sliding. I'll go with the former, but...

Just a few weeks ago, I finally got around to compiling some web statistics and found that the column Illustrated Mac IIci Teardown had been one of my most popular columns in the last twelve months. I'd already planned to do a teardown column on my G3 minitower when I took it apart for cleaning and installation of a 256 MB PC-100 SDRAM chip my honey gave me for my birthday. Don't geeks give nice presents? (My wife, Annie, is a computer and network tech for a large, midwestern banking corporation.) It just seemed like a good idea to go ahead and photograph the teardown and cleanup of the 7500. Actually, the teardown was done without photos. You don't need to see my dust bunnies. When I put the compressor to the power supply, the sunroom was filled with a cloud of dust! I did the photography as I reassembled the 7500, but will present the photos here to represent a disassembly. (Note: You'll notice that as your cursor passes over some of the images they are linked to full size photos. Just click to get a better view.)

Teardown

While most manuals suggest you open up a computer case and then ground yourself out by touching the power supply case, I generally remember what has given me a good static zap during the winter and prefer to unplug everything before opening up a unit. I can always ground myself out by touching a grounded cover plate screw.

7500 frontThe Power Mac 7200 and 7500 introduced a new case design that features easy access to all oft used and upgraded components. Machines with the 7500 form factor, which includes the 7300 and the 7600, are some of the easiest ever made by Apple to service. The 7500 case opens by pressing upwards on two release buttons at the front of the case. Lift the outer case cover upward and towards the front of the computer. Even though I've opened up these cases many times, I still find myself reaching to the rear of the case to open it as one would with the Mac II, Centris/Quadra, and 6100 series machines.

insidesOnce the case is off, all drives are rather easily accessible. The 7500 comes equipped with a floppy drive, a 500-1000 MB hard drive, and a 4X CD-ROM. One extra 3.5" (width) drive bay is provided directly under the main hard drive bay (filled in the pictures left and below). Hard drives and the CD-ROM drive are mounted on plastic sleds. The CD-ROM releases by pushing up on the plastic drive release in the front center of the sled and pulling out the drive. I often just grip the release with a pair of needlenose pliers, lift up and pull (gently!!). I find it easier to remove the 3 cables (power, SCSI, and audio) on the CD after releasing the sled and pulling it forward just a bit.

drive tray closeddrive tray openFrequent reader Tim Baxter pointed out that the top drive assembly pulls out for easier access to releases and cabling. A plastic catch on each side latches the tray. Just pry to the inside and slide the tray towards the front of the computer. One note of caution is necessary. As the plastic ages, it does get brittle. I was a little overenthusiastic with a catch on a 7200 and broke it rather easily! At any rate, I'd never noticed the sliding tray feature until Tim wrote. No wonder it felt so cramped. Thanks, Tim!

drive releaseThe top hard drive sled releases in back by lifting the plastic sled catch and pulling either forward or back and lifting. I got this one wrong in the first writing of this column as well. Thanks to Kyle Hansen for the correction.

floppy release

The floppy drive releases from the top by spreading two plastic retainers and lifting up and towards the rear of the machine. The floppy drive is one of the primary dust catchers of any machine and the 7500's floppy is no different. Dust accumulates from air drawn in by the power supply fan. It's a good idea to hold the floppy drive opening down with a finger holding the drive cover open and give it a good blast of compressed air.

I should mention at this point that I rarely use the commercial canned compressed air at home, as it's just too expensive. Several years ago, I purchased a small compressor to use in the garage and then Annie added a portable tank as a Christmas present. While it's a hassle lugging the portable tank upstairs to my sunroom/computer room, it saves a lot of money on those $4 cans of air! I do, however, still use the commercial stuff on the road when doing repairs. 

Opening the plastic cover on the 7500 case reveals the three PCI slots and the processor daughtercard. There are no latches to be released on the plastic cover. It just pulls up and snaps back shut upon reassembly. I'd wait to pull any processor or PCI cards until the drive chassis on the right is opened. It's not necessary, but it gives a little more working space.

On the computer pictured at left, a Newer Technology MaxPowr G3/250 MHz is installed instead of the 7500's stock PPC 601 100 MHz daughtercard. It has been a trouble free upgrade, but if you are looking to upgrade a Power Mac 7500, there are currently many faster cards for the money than this one. At the time I bought the Newer card, it was the best I could afford.

MaxPowr G3 card

601 daughtercard

Orange Micro 530

Newer MaxPowr G3/250 MHz Daughtercard PowerPC 601/100 MHz Daughtercard Orange Micro PC 530 Windows PCI Card

The PCI card installed is an Orange Micro PC 530 card, which enables me to run Windows apps in Windows 98 at full speed. The card has had a variety of processors installed, including the 166 MHz stock Cyrix chip, an AMD K-6 200 MHz that died when the chip fan failed, and currently an Intel Pentium 133 MHz that came out of one of my daughter's computer when I upgraded it to a K-6/200. Note that Orange Micro no longer produces PC cards.

latchesarmThe chassis that carries the drives and power supply opens up by first folding out the small gray plastic "foot," releasing the center latches towards the center of the computer, and lifting the assembly from the center until it stands securely. An inner support arm extends to hold the case open and must be lifted before closing the case. The photo at right of a support arm is a 1996 photo of our 7200's bar. I've since broken the bar out of both the 7200 and 7500!

With the case completely opened, access to the battery, and PCI, processor, RAM, VRAM, and cache slots is pretty much unobstructed. At this point you should be in pretty good shape to apply a gentle brushing and some compressed air to do a pretty good cleaning of the machine. As I hadn't apparently cleaned my unit for some time, I chose to completely tear it down for a complete cleaning (and a slightly longer column).

If you're going for a complete teardown, ground yourself out again and then pull any installed PCI cards and the processor daughtercard. Be very careful with where you put these cards. A static proof bag for each one is best. Unplug the connectors around the perimeter of the motherboard. Starting near the processor card slot and going clockwise, you'll unplug the AV module cable, the SCSI ribbon, a 22-pin power supply connector, the CD audio cable, the floppy drive ribbon, another power supply cable, the LED cable (It may be easier to just remove the LED assembly from the speaker case.), and the speaker cable. (Click photo at right or here for image of motherboard with cables labeled.)

While not absolutely necessary, I removed the power supply as the next step. You'll need to close the metal chassis and remove the one retaining screw that holds the power supply in place. When reassembling, note the two metal prongs on the chassis that fit into the back of the power supply. It's best to open up the chassis and gently guide the two power cables out through the chassis hole when removing the power supply.

inside case

While the power supply unit is safe enough to handle as a unit, note that it can hold a bunch of power, even when disconnected. There really aren't any user serviceable parts in it, other than the fan assembly. In other words, stay out of the power supply unless you are a trained techie. And...if that were the case, you probably wouldn't be reading this page, anyway:-).

Power SupplyAs this column goes to press, I'm actually awaiting a replacement power supply. I had one fail several years ago, and the current replacement has begun to make more noise than it should. Do note that the 7500 uses a variable speed fan in the power supply, so some noise, especially when it accelerates, is normal. Even after a good cleaning, it still seemed pretty weak upon reassembly, thus, the replacement was ordered. This is probably as good a point as any to note that Apple Computer no longer supports the 7500 with service parts.

speaker screwsIt's a good idea to pull the speaker/LED assembly before removing the motherboard (logic board, if you will). The plastic power switch under the assembly must be removed, anyway. The speaker assembly is held in place by two small torx screws and a plastic catch. Remove the torx screws and press the plastic release catch and remove the speaker assembly. EMI clipYou'll find the speaker case is a big dust catcher and will need some gentle puffs of compressed air to clean. Release the plastic power switch catch from inside the case and remove to the outside of the case, as the motherboard will hang up on it or break the switch if not removed when pulling the motherboard.

Finally, Apple recommends one remove the EMI clip at the back of the motherboard. The service manual states, "Failure to comply may result in damage to the board." While I haven't found it necessary, you've been warned.

If you haven't already done so, go ahead and take out the SCSI and floppy drive cables.

motherboard screwAt last, it's time to remove the motherboard. First, unscrew the plastic center support. While it has grips at the top, I found using a Philips screwdriver down the center hole of the support easier. Release the two plastic catches at the front of the motherboard and gently pull the board towards the front of the machine and lift out.


You will then be left with a gleaming, empty case (after you clean out the dust, of course). The motherboard can be gently brushed and blown clean using a clean, camelshair brush and compressed air. If you've never handled a motherboard before, use two hands. Holding the board by a corner can break it. Also, keep your hands off of anything that looks important. Avoid touching any of the metal connectors as well, as finger grease doesn't do them much good.

7500 motherboardSince we're down to the motherboard, it seems like a good idea to expand upon what some of that stuff is. (Click here for labeled photo.) Towards the front of the board (as it would sit in the case) are eight RAM slots with the cache card slot in between. The 7500 uses 168-pin DIMM chips and can be upgraded one chip at a time. If you use FPM (Fast Page Mode) memory chips, they can be interleaved to achieve improved memory access speed. Use matched DIMMs and slot them A1 and B1, A2 and B2, etc. for interleaving. You can also use 5 volt (not 3.3 volt) EDO chips, according to GURU 2.9, but lose the ability to interleave memory for greater speed.

The cache slot accommodates a 256K, 512K, or a 1 MB Level-2 cache DIMM, according to the Low End Mac 7500 page. If running a G3 or G4 upgrade card as I do, the backside cache usually will give better performance than the motherboard cache. If you're running a 601 or 604 processor daughter card in a 7500, the Level-2 cache will add a good speed kick to your machine's performance. Currently, a 512K Level-2 cache chip will run you around $25.

The four VRAM slots will accommodate up to 4 MB of VRAM. I run just two megs and am able to run pretty much anything I want, occasionally even Nanosaur. However, I don't really do any serious image editing on this machine. The one time we had any trouble that may have been due to insufficient VRAM was when I loaned out the 7500 to my school's technology coordinator. He connected a projector to it, which knocked out the display. Whether it was too much of a RAM requirement, running the video through the Orange card, or just a problem with refresh rates I never figured out.

There's also a DAV (Digital Audio Video) slot and ROM SIMM slot on the motherboard that I've never had reason to use. One Apple Tech Info document notes that there were some problems with the DAV slot in some 7500 and 8500's, as does the service manual for this model.

If you have used this page to take your 7500 apart, just reverse the steps to get it back together. While I've had to strip this machine down to the motherboard a number of times for upgrades and repairs, I'd never actually pulled the board until I decided to do this column.

This is the machine that serves as my primary computer at school. It contains all of the reading, spelling, and math files that we regularly print out for student use. It's second drive is devoted to carrying the Orange Micro application and the "C drive" for the Windows files. I use this machine to write some of the IEP's (Individualized Educational Plan) required for each student in my class, and it contains the master file of all of the IEP's for reporting out to parents each grading period. While the monitor and keyboard for the school's 8550 Mac server sit near the 7500, I usually access and maintain the server remotely from the 7500.

Just two weeks ago I'd written in the column Great Classroom Computer Buys: When the Worst Can Turn Out to be the Best, "I like my 7500, especially its video capabilities, but certainly don't love it." Tearing down and analyzing the 7500's motherboard has added a bit more respect for the model.

I've hunted most of the summer for an inexpensive G3 desktop or minitower to replace the 7500, as it is seriously aging, but found no bargains. That precipitated swapping out the power supply and floppy drive during the teardown and cleanup of this machine. If I get lucky and still find an absolute steal on a G3, the 7500 will probably stay home with our youngest child. At any rate, it should now have at least another year of life left in it.

Other Power Mac 7500 Info

Maybe a Really Happy Ending for the 7500 (3/15/03)

I permanently took my Power Mac 7500 out of classroom service today. I moved its hard drive, some of its RAM, and the Newer G3 processor card into a Power Mac 7600 I picked up a few weeks ago.

What happens now to this excellent workhorse of a computer? It's already in a teardown, cleaning, and refurbishment phase. Rather than use the stock 601/100 processor card that came with the 7500, it now sports the 7600's 604/132 MHz processor card. In April, it will go back to school for a week for one of my students to get to know the machine. Then it goes home with him as part of our student computer loan-own program.

What a happy ending.

Update (5/9/2008)

Power Mac 7300 Motherboard

Even though Illustrated Power Mac 7500 Teardown remains one of my most read columns, I'd avoided updating it for some time. The original photos were done with a rather low resolution digital camera, and as mentioned above, the 7500 had gone elsewhere. I realized while recently cleaning up my sunroom/computer workshop that I could probably replicate some of the chassis shots with my dad's old Power Mac 7300 (which still had the Newer G3 card installed!). The motherboard (shown at right) and processor are the main differences in the models. His old computer became surplus when my brother and I got him a new iMac a year or so ago. Dad will be 95 in a few days and still sends out regular emails to his kids! He started with his first computer when he was 87!

I retained some of the original photos from 2001, as they were still useable with a bit of lightening, some added contrast, and a bit of the sharpen filter. I also followed one excellent suggestion a reader sent in a few years ago. He made a kind request that I NOT use red labels. The reader was color blind and the red labels made things very difficult for him to read. And actually, many of the original labels were a bit difficult for the color sighted as well! Thus, the labels on newer graphics and those I reworked are now either white on black or black on white.

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all links checked and updated 8/29/2010
©2001 Steven L. Wood