Introduction

Struggling with sudden shutdowns in your GE 90-70 PLC system? Power supply failures often start small but halt entire operations. As someone with 15 years in industrial automation (Bentley Nevada, GE, AB), I've seen how quick checks prevent costly downtime. Let's diagnose it step-by-step.

GE 90-70 power supplies are workhorses, but age, voltage spikes, or dust can cripple them. Most failures trace back to fuses or unstable voltages. Catching issues early saves hours of troubleshooting. Follow this field-tested guide.

Common Culprits Behind Power Supply Failures

From my experience, 80% of failures stem from:

• Blown fuses from inrush currents
• Voltage irregularities (input/output)
• Overheating due to clogged vents
• Capacitor aging - bulging tops mean trouble

Pro Tip: Always check power quality first - dirty electricity kills PSUs faster than workload.

Step 1: Safety First - Prepare Your Workspace

Disconnect ALL power. Wait 10 minutes for capacitors to discharge. Use gloves and insulated tools. I’ve seen "dead" units hold 240V – safety isn’t optional.

Step 2: Fuse Check - The Quick Fix (Often Missed!)

Locate fuses (typically 5A-10A glass/ceramic tubes near input terminals). Test continuity with a multimeter. No beep = blown fuse. Replace with identical specs ONLY.

Unique Insight: If a new fuse blows instantly, stop. You likely have a short circuit downstream – often a failed MOV or diode.

Step 3: Input Voltage Testing

Reconnect power cautiously. Set multimeter to AC voltage. Test L1/L2/N terminals:

• Expected: 120VAC or 230VAC (±10%)
• Fluctuations >15%? Check your mains supply.

Low voltage strains components. High voltage kills them.

Step 4: Output Voltage Verification

Switch multimeter to DC. Probe +24V and COM terminals:

• Healthy range: 23.5V - 24.5V
• <24V under load? Capacitors are likely dying.

Pro Tip: Test under 50%+ load – weak PSUs fail when stressed.

Step 5: Visual Inspection & Thermal Clues

Power down again. Look for:

• Burnt smells/discoloration
• Bulging/leaking capacitors
• Cracked solder joints

Use a thermal camera if available. Hot spots >85°C signal component failure.

When Replacement Becomes Smarter Than Repair

If voltages drift or fuses keep blowing, your PSU is fatigued. GE 90-70 modules last 8-12 years. Beyond that, replacements beat repair costs.

Need a reliable drop-in solution? Ubest Automation Limited stocks tested, compatible GE 90-70 power supplies with 18-month warranties. We ship globally – get backup units before failure strikes.

Summary: Start with fuse/voltage checks – they solve 60% of GE 90-70 PSU failures. When components age, quality replacements prevent cascade failures. Document your readings; patterns reveal hidden issues.