Power Macintosh 7200 General Maintenance

Power Macintosh 7200/90. Photo: Olli1800, Wikimedia Commons, CC BY-SA 3.0

These procedures for the Power Macintosh 7200 come from Apple's Power Macintosh 7200 Series/WS 7250 Service Source, which covers the 7200/75, 7200/90, 7200/120 and Workgroup Server 7250/120. The 7200 uses the same case, hinged internal chassis and power supply as the 7300, 7500 and 7600, so Power Macintosh 7500 General Maintenance applies to the case and supply as well. The 7200 differs from those machines in its soldered processor and optional processor fan, its soldered VRAM and its memory rules.

Mains voltage is present inside the power supply whenever the computer is plugged in, and the supply's 5 V trickle output stays live while it is plugged in, even when the computer is off. Unplug the computer before opening it.

Before you start

The power supply has a voltage switch on the back panel, set to 115 for 100–130 V or 230 for 220–270 V. Check it on any machine of unknown history before plugging it in; Apple's User's Guide warns that a wrong setting damages the computer. Lift the computer by its sides; lifting it by the front and back can make the cover come off (User's Guide PDF p. 15).

Opening the case

1. Press the two tabs at the front corners of the top housing, pull the housing forward 1 to 2 inches and lift it straight up (SS pp. 69–71).
2. Release the chassis latches, flip open the chassis support foot and swing up the internal chassis that holds the drives and the power supply (p. 93).
3. If a processor fan is plugged into the logic board at J70, unplug it as the chassis swings up, and plug it back in before closing (p. 93).
4. To keep the chassis up, flip down the support arm and seat its tab in the hole in the bottom chassis. Apple warns never to work with the chassis up unless the arm is down and fastened (p. 99).

With the chassis up, the DIMM, VRAM and cache slots and the battery are accessible (dev note p. 3; SS p. 93). The three PCI slots are reached by swinging open the expansion card cover (pp. 118–120).

Memory and video RAM

The 7200 has no RAM on the logic board, and at least one DIMM must be fitted. Use 5 V, 168-pin, 64-bit fast-page-mode DIMMs of 70 ns or faster, in any of the four slots and in any order. The memory controller does not interleave, so pairs bring no speed gain, though Apple recommends DIMMs of the same size and speed (SS pp. 9–12). Earlier Macintosh SIMMs do not fit.

One megabyte of VRAM is soldered to the board. For 2 MB fit one 1 MB VRAM DIMM in slot 1; for 4 MB fit three, in slots 1, 2 and 3. Slots 2 and 3 must be filled together. VRAM DIMMs are 112-pin, 70 ns or faster. Push the release latch to remove one; press a new one in evenly until the latch clicks (pp. 121–125).

The cache slot takes a 256 KB L2 cache DIMM (SS p. 31); Apple's developer note gives 256 KB, 512 KB or 1 MB as the sizes the slot accepts (pp. 5, 14).

Clock battery

The battery sits near the front left corner of the logic board. Swing up the internal chassis, prise up one side of the battery cover with a screwdriver and lift the battery out (SS pp. 92–95). Apple's specification pages give it as a 3.6 V lithium cell, and the bill of materials bound with the logic board schematic lists a half-AA holder (525-0055) and cover (520-0344). Fit the new cell the right way round (p. 18).

The 7200 Service Source gives no voltage below which to replace the battery; its charts only say "Check battery" for a computer that shuts down intermittently (p. 49). A clock that loses time is the User's Guide's sign of a failing battery (PDF p. 86). A leaking lithium cell leaves acidic residue: neutralise it with bicarbonate of soda solution, rinse with isopropyl alcohol and check the nearby traces. See Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.

Resets

The Cuda microcontroller switches the power supply on and off, handles resets, keeps PRAM and the clock and runs ADB. Press the Cuda reset button on the logic board to reset it; Apple's logic board diagram shows where it is (SS pp. 17, 23).

Apple's logic board reset is the first step for a 7200 that will not power up (pp. 18–19):

1. Unplug the computer.
2. Remove the battery.
3. Disconnect the power supply cable from the logic board and press the Power On button.
4. Wait at least 10 minutes, then refit the battery the right way round.
5. Reassemble and test. The reset clears PRAM, so set the date, time and other settings again.

To clear PRAM without opening the case, hold Command-Option-P-R at startup before "Welcome to Macintosh" appears (p. 50).

Power supply

To remove the power supply (SS pp. 96–104):

1. Disconnect the power cables from the back of the CD-ROM drive and the hard drive.
2. Swing up the internal chassis and lock it with the support arm (unplug the J70 fan first if fitted).
3. Disconnect both power supply cables from the logic board: the 22-pin cable (5 V and ±12 V) and the 10-pin cable.
4. Remove the two screws at the back that hold the supply to the chassis.
5. Release the support arm and swing the chassis down.
6. Slide the supply forward and lift it out, feeding its logic board cables up through the hole in the chassis.

When refitting, slide the supply back until the two metal tabs on the chassis lock into it, and check the voltage switch, which is reached through the rear panel (pp. 103–104). The service part is 661-0920 (p. 157). The connector pinouts and the community repair notes are on Power Macintosh 7200 Troubleshooting.

Processor fan

Only some 90 and 120 MHz logic boards have the fan; the exploded view lists fan 922-1736 for use with logic board 661-0979 (pp. 135, 157). To replace it, unplug its connector from the logic board, swing up the internal chassis and remove the two screws that hold it. Plug it back in before refitting the top housing (pp. 135–139).

Logic board

Remove the top housing, PCI cards, speaker and power actuator first (SS p. 127).

1. Swing open the expansion card cover, then swing up the internal chassis.
2. Disconnect both power supply cables, the floppy cable, the SCSI cable and the CD audio cable, then the LED and speaker cables.
3. Remove the screw inside the top column support.
4. Press down the two tabs at the front of the board, slide it forward away from the rear panel and lift it out.
5. Lift the EMI clip off the top edge of the board. Apple warns that leaving it on when the board is out can damage the board.

Remove the cache, DRAM and VRAM DIMMs before sending a board away, but leave the ROM SIMM where one is fitted (pp. 127–134). Apple's Peltier device on the processor must stay plugged into the board (p. 22).

Cleaning

Residue on the gold edge connectors of PCI cards can cause a range of faults. Inspect the pins with a magnifier and clean them gently with a pencil eraser (SS p. 44). Keep the vents clear: the thermal protection circuit shuts the computer down when it overheats (p. 49).

Drives

The hard drive is in the top left bay, the floppy drive in the top right and the CD-ROM drive in the bottom right. The hard drive and CD-ROM drive slide out once their retaining clips are lifted; the floppy drive comes out when its plastic rails are pulled out (SS pp. 74–86). Only the last device on the SCSI chain should be terminated (p. 59). When replacing the floppy drive, move the EMI gasket to the top of the new drive with the "V" pointing to the front; the gasket is 922-1895 (p. 82). See Hard Drive Maintenance and Repair and Floppy Drive Repair.

Related pages

• Power Macintosh 7200
• Power Macintosh 7200 Troubleshooting
• Power Macintosh 7200 Capacitor Replacement Guide
• Power Macintosh 7500 General Maintenance
• Recommended Tools