Apple Monitor II Troubleshooting Guide

Apple Monitor II (Ben Boldt, Wikimedia Commons, public domain)

Fault-finding on the Apple Monitor II (A2M2010) and the Apple Monochrome Monitor IIe (A2M6017), from Apple's symptom chart, the owner's chart in the user's manual, and the circuit checks in Sams's ComputerFacts for the monitor. Apple treated the main electronics assembly as an exchange module, so its chart ends at board level. Sams goes further, with test voltages and the components to check in each circuit.

The anode runs at about 13 kV and the board work below is done with the back off. Read CRT Discharge Procedure first, and see Apple Monitor II General Maintenance for opening the case and the two safety checks Apple asks for on older units.

Before opening the monitor

Apple's user's manual covers the faults that need no tools.

From the Monitor II User's Manual

Symptom	Cause	Action
Unusual sounds or smells	Electronics overheating	Unplug power and video at once
No picture, switch on, power light out	Not plugged in, dead outlet	Check the plug, outlet, fuse or breaker
No picture, switch on, power light on	Video cable not connected, or contrast or brightness turned too far	Reconnect the video cable; turn contrast, then brightness, until the picture appears
Display vibrates slightly	Input signal from the computer	Check the computer
Picture rolls up or down	Vertical hold misadjusted	Turn the vertical hold on the back
Characters too tall or too short	Vertical size misadjusted	Turn the vertical size control on the back

The monitor takes composite video through the phono jack. Try it on another Apple II, or try the computer on another monitor, before blaming either.

Apple's symptom chart

Apple's actions are listed in the order Apple gives them.

Monitor II symptom chart (Technical Procedures pp. 4.3-4.6)

Symptom	Actions
No raster	Check the fuse on the filter board; check that all connectors on the filter board and main electronics assembly are secure; replace the power switch; replace the filter board; replace the main electronics assembly; replace the power transformer; replace the CRT
One horizontal line	Replace the main electronics assembly; replace the yoke
One vertical line	Replace the main electronics assembly; replace the yoke
Raster deformed	Adjust the yoke; replace the yoke
Raster winds or the picture fluctuates badly	Replace the main electronics assembly
Spot stays on the screen after switch-off	Replace the main electronics assembly
Brightness range abnormal	Replace the main electronics assembly; the filter board; the power transformer
Small raster, abnormally bright picture (high voltage too high)	Replace the main electronics assembly
No vertical sync	Replace the main electronics assembly
Raster not centred	Turn the yoke centring magnets
Picture or characters tilted	Turn the deflection yoke
Fine noise in the picture, characters shiver	Replace the main electronics assembly
Picture takes 15 seconds or more to appear	Replace the CRT
Picture appears and disappears	Replace the main electronics assembly; replace the CRT
Horizontal linearity bad	Check the horizontal adjustment; replace the main electronics assembly
Vertical linearity bad	Check the vertical adjustment; replace the main electronics assembly
Will not focus	Replace the main electronics assembly; replace the CRT
Wavy display	Mounting screw on the regulator heat sink is loose

Apple's note on the last line: if the picture goes wavy once the monitor has warmed up, the 7815 regulator IC601 is overheating because the screw holding it to its heat sink is loose. Refit it with thermal compound or an insulator pad.

Board-level checks

Sams's troubleshooting section, by circuit. Component numbers are those on the main board, 060-01-001.

Power supply

1. If fuse F601 is open, check capacitors C701-C704 on the filter board, transformer T601, bridge diodes D601-D604 and the regulator IC601 before fitting a new fuse.
2. With the fuse good, apply 120 V AC and measure 22.5 V at the cathode of D604. If it is missing, check the power switch S601 and the AC line filter.
3. With 22.5 V present, measure 14.9 V at pin 3 of IC601. If it is missing, check IC601 and the horizontal output transistor Q401. If it is present, go to the horizontal checks.

Apple's schematic shows the bridge as four 1N5402 diodes feeding a 3300 µF 35 V reservoir (C601) ahead of the regulator.

Horizontal

1. Measure 14.9 V at the collector of the horizontal output transistor Q401. If it is missing, check R420, D403 and the power supply. R420 is a 0.5 Ω 1 W metal-oxide resistor that also acts as a fuse.
2. With 14.9 V present, inject a horizontal signal at the base of Q401. If deflection returns, check pins 1, 2, 4, 5, 6, 11, 12, 13, 14 and 15 of the deflection IC IC401 (TDA1180P) and their components.
3. If there is still no sweep, check the horizontal output transformer T401. Its high-voltage rectifier is built in, and a fault there also upsets the horizontal circuits.
4. If the oscillator is off frequency, check pins 13, 14 and 15 of IC401.
5. Horizontal linearity or foldover faults can come from C414, C415 and C420 or from the coils L401 and L402.

Vertical

1. Check the supply voltages on the vertical output IC IC301 (TDA1170N).
2. If they are right, look for a vertical waveform at pin 4 of IC301.
3. With a waveform at pin 4 but no deflection, check the electrolytic C308 and the yoke. Sams also names C209, C303 and C307.

Video

1. Inject a video signal at the input jack and look for it at the CRT.
2. Check the video amplifier transistors Q101, Q102, Q201 and Q202 and the blanking transistors Q203 and Q204.
3. Weak brightness or contrast: check the contrast control R108, the internal brightness control R506, and the voltages on pins 1 and 5 of the CRT.

Sync

1. No vertical or horizontal sync: look for a video waveform at the collector of the sync separator Q104.
2. No vertical sync with Q104 working: check pins 8, 9 and 10 of IC401. No horizontal sync: check pins 8, 9, 13 and 15 of IC401.

Self-inflicted faults

• The SW (power switch) and T1 (transformer) leads on the filter board are both two-hole connectors and fit each other's posts. T1 also has to go on the right way round, by the B and W marks.
• The right-rear corner of the main board is glued as well as screwed. Prising the board up without first cutting the glue breaks the corner.
• Overtightening the yoke clamp screw can crack the tube neck.

Related pages

• Apple Monitor II
• Apple Monitor II General Maintenance
• Apple Monitor II Capacitor Replacement Guide
• Apple Monitor II Documentation
• Capacitor Failure Symptoms