231-B900

Check PSU Status LEDs

Examine the power supply unit status indicators on the main cabinet. Green LEDs should be solid, red indicates fault conditions.

Ensure main power is locked out before opening electrical cabinet

Measure DC Voltages

Using a multimeter, verify +15VDC and -15VDC rails at the PSU output terminals. Acceptable range is typically ±14.25V to ±15.75V.

Check voltages under load - some PSUs fail only when loaded

Inspect PSU Connections

Verify all DC output connections from PSU to CC board are tight and show no signs of arcing or overheating.

Loose connections can cause voltage fluctuations and intermittent alarms

Replace PSU if Faulty

If voltages are out of specification, replace the power supply unit with Heidenhain-approved equivalent and clear alarm via MOD function.

Always verify part numbers match exactly - voltage ratings are critical

Count Connected Encoders

Document all encoders connected to the CC board +5V supply. Check machine parameter MP7440 (encoder supply configuration) for maximum allowable load.

Linear encoders typically draw 150-200mA, rotary encoders 80-120mA

Measure +5V Current Draw

Using clamp meter on +5V supply line, measure total current consumption. Compare against CC board specifications (typically 2A maximum).

Disconnect encoders one at a time to isolate high-current devices

Check Encoder Cable Integrity

Inspect encoder cables for damage, moisture ingress, or short circuits that could increase current draw beyond normal operating parameters.

Megger test encoder cables at 500VDC to verify insulation integrity

Install External +5V Supply

If total load exceeds CC board capacity, install dedicated external +5V encoder supply and modify wiring accordingly.

Ensure common ground reference between CC board and external supply

Visual Inspection of CC Board

Remove CC board and inspect for bulged capacitors, burned resistors, or discolored components around voltage regulation circuits.

Handle CC board with proper ESD precautions - use grounded wrist strap

Check Board Temperature

Using infrared thermometer, verify CC board operating temperature is within 0-55°C range. Hot spots indicate component stress.

Clean cooling fans and heat sinks - thermal issues accelerate component aging

Test Voltage Regulation Circuits

With board powered, measure voltage regulation IC outputs using oscilloscope to check for ripple, noise, or instability.

Look for >100mV ripple on DC supplies - indicates failing filter capacitors

Replace CC Board

If voltage regulation circuits are faulty, replace CC board with new unit and transfer configuration parameters via TNC backup/restore function.

Backup all machine parameters before CC board replacement

Inspect for Contamination

Remove CC board and examine for coolant residue, oil films, or metallic particles that could create unwanted electrical paths.

Power down completely before removing CC board for inspection

Clean Board Thoroughly

Use isopropyl alcohol (99%) and lint-free cloths to clean all contamination from board surfaces, paying attention to connector areas.

Use soft brush to remove debris from component leads and socket connections

Check Cabinet Sealing

Inspect electrical cabinet door seals and cable glands for proper sealing to prevent future contamination ingress.

Maintain positive cabinet pressure where possible to exclude contaminants

Test After Cleaning

Reinstall cleaned CC board, power up system, and monitor for alarm recurrence over several operating cycles.

Allow 30-minute warm-up period before declaring repair successful

Verify Ground Integrity

Check continuity between CC board ground, cabinet ground, and machine ground using low-resistance ohmmeter. Resistance should be <0.1 ohms.

Look for corroded ground straps or loose ground connections

Check EMI Shielding

Inspect cable shielding connections and ferrite cores on encoder cables. Ensure shields are properly terminated at both ends.

Never ground cable shields at both ends - creates ground loops

Isolate Interference Sources

Temporarily disconnect VFDs, welders, or other high-power equipment to determine if EMI is triggering false voltage alarms.

Use oscilloscope to capture voltage waveforms during alarm occurrence

Install EMI Filters

Add line filters or improve cable routing separation between power and signal cables to reduce electromagnetic interference.

Maintain minimum 6-inch separation between power and encoder cables