Macintosh Color Classic General Maintenance

Macintosh Color Classic

Maintenance guidance for the Macintosh Color Classic, also sold as the Macintosh Performa 250. It is a compact Macintosh with a 10-inch Trinitron CRT, a logic board that slides out of the back, and a combined analogue board and power supply with a universal 90–240 V AC input. The two jobs that matter most on an unrestored machine are the PRAM battery and the logic board capacitors; both are reached without opening the case.

Safety

The CRT and the analogue board hold dangerous voltages after the machine is unplugged. Read CRT Discharge Procedure before removing the rear housing. Apple's warnings for this machine:

• Never touch the anode or hold the CRT by its neck; the neck breaks easily and the anode may retain high voltage.
• The whole yoke assembly carries very high voltage during adjustments. Do not touch the yoke, the anode wire or the yoke wires.
• Do not use metal alignment tools on the adjustment controls; they are a shock hazard. Use a short, rigid hex-head plastic tool.
• Do not wear a grounding wriststrap until the CRT has been discharged.

Apple's Service Guide CRT rules for Macintosh computers put the anode at up to 12,000 V DC.

Removing the logic board

Apple's procedure needs no other preparation:

1. If fitted, remove the two security screws from the I/O door.
2. Push down the two latches until the I/O door snaps open, and remove it.
3. Grasp the logic board with both hands and pull it straight out onto a grounded mat.

When refitting, check that no bent metal tab on the chassis can touch the underside of the board and short it.

Opening the case

Only needed for the analogue board, CRT, drives or fan.

1. Remove the four case screws with a long-handled Torx driver, and the two I/O door security screws if fitted.
2. Separate the rear housing from the chassis with a case spreader and lift it away. The chassis edges are sharp.
3. Discharge the CRT and remove the anode cap before touching the analogue board.

All from Apple's Take Apart. To replace a damaged rear housing, the fan comes off it first; the fan unclips from the housing with two latches.

With the rear housing off, Apple warns that the metal chassis can buckle and short to the bottom of the logic board. Check the chassis is clear of the board before switching on, and support its rear corners during adjustments.

PRAM battery

Apple's procedure is to remove the logic board, set the meter to the 10 V DC range and replace the cell if it reads below 3.0 V. To remove it, lever each end of the holder cover off with a small flat-blade screwdriver and lift the cell out. Apple's warning: "If handled or discarded improperly, the lithium battery in the computer could explode."

Apple describes the cell only as a long-life lithium battery. Low End Mac reports that most Color Classics use a 3.6 V half-AA cell and some a 4.5 V Rayovac 840, so check what is fitted before ordering. Clean lithium-cell leakage with bicarbonate of soda, then water and isopropyl alcohol; vinegar is for the alkaline 4.5 V packs in the Macintosh Plus and Macintosh 512K. Remove the cell from a machine going into storage. See Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.

Capacitors

The logic board's surface-mount electrolytics leak. Recap-a-Mac finds four leaky capacitors around the sound chip at the top left of the board and usually has to repair traces there, and says an unrecapped Color Classic "is living on borrowed time". On the analogue board it singles out the 3300 µF 16 V capacitor near the middle, which can leak and disturb the display. Lists and procedure: Macintosh Color Classic Capacitor Replacement Guide. See also Capacitor Failure Symptoms.

Analogue board

Apple treats the analogue board and power supply as one module, 661-0732. Its primary reservoir, CP30, is a 330 µF 400 V capacitor; on 240 V mains it charges to about 340 V DC, so never fit a 250 V part there.

TinkerDifferent members report the paralleled 18 V zener diodes DL21 and DL22 scorching the board beneath them, and the 47 Ω resistor RL62 burning; uprated replacements are listed on the capacitor guide. Inspect that area whenever the board is out.

The machine has a fan, a separate module clipped into the rear housing, and a degauss coil around the CRT. Check that the fan turns.

Apple publishes no rail tolerances and no power-supply adjustment for the Color Classic. The "+5 V 4.85–5.15 V / +12 V 11.90–12.75 V" pair quoted for compact Macs is Apple's Macintosh Plus procedure and does not apply. Measure each rail against its nominal value at the logic board connector.

Display adjustments

Apple's Adjustments chapter covers geometry, video, convergence, geometric distortion, yoke and light meter setup. Adjustments are made from the rear with the housing off and a mirror in front of the screen, using Apple's Display Service Utility test patterns.

Color Classic display adjustments (Apple)

Adjustment	Apple's target or method
Vertical size	Raster 4.9 in (± 1/16 in), 124.5 mm (± 1.5 mm) high on an all-white screen
Horizontal size	Raster 6.7 in (± 1/16 in), 168.5 mm (± 1.5 mm) wide
Vertical and horizontal centre	Raster centred in the display area
Focus	Focus test pattern as clear as possible
Cutoff	After at least 10 minutes' warm-up; required whenever the analogue board is replaced, and before white balance
White balance	No predominant colour in the four darkest and four brightest gray bars
Sub-contrast	37 foot-lamberts (± 3) on an all-white screen
Convergence	Convergence control on the CRT video board, then N/S correction, E/W correction and E/W amp
Geometric distortion	Pin phase (KS), vertical angle (PR), horizontal bow (PB), in that order if the distortion is severe
Yoke tilt	Rotate the yoke collar with the clamp screw loosened; tighten it with the power off and the CRT discharged

Apple's first step for a tilted, distorted or off-centre raster is to move the machine to a different location, to rule out its surroundings.

Not a fault

"A thin, gray, horizontal line may be visible across the bottom third of a lit screen. This line is inherent in the design of Trinitron monitors. Do not replace modules." This note is in the 141-page copy of Apple's manual and missing from the 139-page copy.

Environmental specification

Apple's environmental figures

Item	Figure
Operating temperature	10–40 °C (50–104 °F)
Storage temperature	−40 to 47 °C (−40 to 116 °F)
Relative humidity	20–95 % non-condensing
Altitude	0–15,000 ft

From the Environmental page of the Specifications chapter. Keep the vents clear.

Tools

• Long-handled Torx driver and a case spreader
• CRT discharge tool
• Short, rigid hex-head plastic alignment tool (not metal) and a mirror
• Anti-static wriststrap and mat
• Multimeter
• Isopropyl alcohol and a soft brush

See Recommended Tools.

Related pages

• Macintosh Color Classic
• Macintosh Color Classic Capacitor Replacement Guide
• Macintosh Color Classic Troubleshooting
• Macintosh Color Classic Service Source
• CRT Discharge Procedure
• Sad Mac Error Codes