Woodward Spm A Synchronizer Model 9907 029 Troubleshooting
Your Woodward SPM-A synchronizer is refusing to lock onto the bus. The generator hunts, the sync relay stays open, or that red ALARM light just stares back at you. Woodward Spm A Synchronizer Model 9907 029 Troubleshooting doesn't need to be a guessing game when you know what the board is actually telling you.
Manufacturer specifications indicate the unit operates within a slip frequency window of 0.05 to 0.5 Hz and a phase angle window of ±5° to ±20°. When those parameters drift, the board has specific ways of signaling the problem. Let's walk through what each signal means and what to check next.
Quick Answer
Start with the front-panel LEDs. Run through the symptoms systematically. Measure test points TP1 through TP4.
Check the sync window potentiometers. Verify phase rotation and CT polarity. Replace the internal fuse if blown.
Adjust the DROOP, SPEED, and LOAD pots in sequence. Always power down and lock out before touching terminals.
The SPM-A Won't Sync: Where to Start
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You have a generator that needs to parallel with a live bus. The SPM-A should handle the closing sequence automatically. When it doesn't, the first thing to check is power.
The board needs 120 or 240 VAC at terminal block TB1. Grab a multimeter and confirm voltage is present.
If power is good, look at the internal fuse. It's a 1A slow-blow, 250V unit. A blown fuse means no power reaches the control circuitry.
Replace it once and see if the board wakes up. If it blows again, you have a short somewhere. Check the relay contacts and the wiring to the actuator.
Step 1: Let the LEDs Tell You What's Wrong
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The front panel has three LEDs. Each one tells a story. The green RUN light means the board has power and the microprocessor is alive.
No RUN light means no power or a dead board. Check the fuse and the power supply first.
The green SYNC light comes on when the generator is within the sync window. It should flash as the slip frequency approaches zero. If it stays solid or stays off, the PLL circuit isn't locking.
That points to a bad phase-lock loop or incorrect phase rotation.
The red ALARM light is the most useful. It triggers when the sync relay fails to close within the programmed time window. That usually means the generator isn't coming close enough to match the bus.
Check the sync window potentiometer settings and the speed bias signal.
Step 2: Diagnose by Symptom (Hunting, Dead Bus, or False Sync)
The Generator Hunts
Hunting means the engine speed oscillates around the target. The SPM-A sends a speed bias signal to the governor. If that signal is noisy or unstable, the generator hunts.
Check the wiring between the SPM-A and the governor. Loose terminals cause intermittent signals.
If the wiring is solid, the DROOP potentiometer may be set too high. Back it off slightly and see if the oscillation dampens. The load signal from the CT also affects hunting.
Verify the CT polarity is correct. A reversed CT signal sends the wrong feedback to the board.
Dead Bus Won't Close
The SPM-A has a dead bus logic. If the bus voltage is below a threshold, the board should close the generator onto a dead bus automatically. When it doesn't, check the dead bus relay.
It's a separate relay inside the unit. Measure continuity across the contacts.
Also check the bus voltage sense wiring. If the board sees voltage on the bus when there isn't any, it won't close. A failed voltage sense transformer can cause this.
Test the bus voltage at the terminal block with the generator off.
False Sync (Out of Phase)
False sync is dangerous. The relay closes when the generator is not in phase with the bus. This usually means the phase rotation is wrong.
Use a phase rotation meter to verify the generator and bus are the same sequence. A reversal of two phases causes the SPM-A to see a false match.
The sync window potentiometer may also be set too wide. If the window is ±20°, the board allows a larger phase error. Tighten it to ±5° and test again.
The sync time potentiometer should be set to 2 to 5 seconds. Too short a window causes premature closure.
Test Point Measurements: The Quick Check
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The SPM-A has four test points on the board. You can measure them with a standard multimeter. TP1 is the sync voltage from the generator.
TP2 is the bus voltage. Both should read between 0 and 10 VDC when the generator is running. A zero reading means a bad sense transformer or wiring.
| Test Point | Signal | Expected Range | What It Tells You |
|---|---|---|---|
| TP1 | Generator voltage | 0–10 VDC | Generator sense circuit works |
| TP2 | Bus voltage | 0–10 VDC | Bus sense circuit works |
| TP3 | Speed error | 0–10 VDC | How far from target speed |
| TP4 | Load signal | 0–10 VDC | CT polarity and load sharing |
TP3 shows the speed error. A reading near 0 V means the generator is close to synchronous speed. A reading near 10 V means it's far off.
Adjust the governor until TP3 reads under 1 V. The SPM-A then takes over the final adjustment.
TP4 is the load signal. It comes from the current transformer. A reading of 0 to 5 V means the generator is underloaded. 5 to 10 V means it's near full load.
If TP4 reads 0 V when the generator is loaded, the CT polarity is reversed or the wiring is broken.
Common Mistakes That Cost You Time (and Parts)
The biggest mistake is replacing the board when the problem is a loose wire. Check every terminal connection before you order a new SPM-A. Loose terminals cause intermittent faults that mimic a dead board.
Tighten them all with a small screwdriver.
Another common error is setting the sync window too wide. A ±20° window might close the relay when the generator is still out of phase. That causes a reverse power trip and potential damage.
Start with ±5° and widen only if the unit won't sync within 10 seconds.
People also skip the phase rotation check. They assume the generator and bus are wired correctly. Always verify with a phase rotation meter.
A single reversed phase causes the SPM-A to see a false match. The relay closes, the generator trips, and you're back to square one.
Ignoring the CT polarity is another time sink. The load signal from the CT must be in the correct direction. If the CT is reversed, the SPM-A sends the wrong speed bias signal.
The generator hunts or fails to share load. Reverse the CT leads and test again.
Finally, don't adjust all the potentiometers at once. Change one at a time and test after each adjustment. Mark the original position with a pencil so you can return to it.
Random tweaks make the problem worse and leave you with no reference point.
Safety First: What You Must Know Before Touching the Board
The SPM-A operates with line voltage. 120 or 240 VAC is present on the board even when the generator is off. Touching the wrong terminal can cause a serious shock. Always follow lockout/tagout (LOTO) procedures before opening the panel.
The internal capacitors can hold a charge after power is removed. Wait at least five minutes after disconnecting power before touching any component. Use a voltmeter to confirm zero voltage at the terminal block.
Insulated tools are cheap insurance.
| Safety Hazard | What to Do | What Not to Do |
|---|---|---|
| High voltage (120/240 VAC) | Lock out and tag out the supply | Work on a live board |
| Rotating generator | Disconnect the engine start signal | Assume the engine won't crank |
| False sync (out of phase) | Verify phase rotation with a meter | Close the breaker manually |
| Stored charge in capacitors | Wait 5 minutes after power off | Short the terminals with a screwdriver |
The biggest risk is a false sync. If the relay closes when the generator is out of phase, the mechanical stress can damage the engine and generator. The electrical fault can blow fuses and trip breakers.
Always verify the sync window settings before testing.
Frequently Asked Questions
Why is my SPM-A not getting power?
Check the fuse first. It's a 1A slow-blow, 250V unit at the top of the board. If the fuse is good, measure voltage at terminal block TB1.
You need 120 or 240 VAC between the L and N terminals. A tripped breaker or loose wire is the common cause.
What does the red ALARM light mean?
The red ALARM light means the sync relay failed to close within the programmed time. The board tried to synchronize but the generator never came close enough to the bus. Check the speed bias signal, the sync window settings, and the governor response.
How do I adjust the sync window?
The sync window potentiometer is labeled SYNC WINDOW on the board. Turn it clockwise to widen the window or counterclockwise to narrow it. Start at ±5° and increase if the unit won't sync within 10 seconds.
Mark the original position before you start.
Can a bad CT cause the SPM-A to hunt?
Yes. A reversed or damaged CT sends the wrong load signal to the board. The SPM-A then adjusts the speed bias in the wrong direction.
This causes the generator to hunt. Check the CT polarity by measuring TP4. A reading near 0 V with load on the generator means the CT is reversed.
What is the dead bus mode?
Dead bus mode allows the SPM-A to close the generator onto a bus with no voltage. The board detects the missing bus voltage and closes the sync relay immediately. If the dead bus relay doesn't close, check the bus voltage sense wiring and the dead bus relay contacts.
Decision Guide: Your Next Step Based on Symptom
Use this quick guide to pick the right diagnostic path. Start with the symptom you see on the front panel.
No RUN light. Check the power supply and the internal fuse. If the fuse is blown, replace it and test. If it blows again, look for a short in the relay contacts or wiring.
RUN light on, SYNC light off. The generator is not close to synchronous speed. Measure TP3. If it reads above 1 V, adjust the governor.
If it reads near 0 V, check the phase rotation and the sync window settings.
SYNC light flashing but relay never closes. The generator is coming close but not staying inside the window. Widen the sync window slightly. Check the speed bias signal for noise.
Loose terminals cause intermittent signals.
ALARM light on. The sync relay timed out. Shorten the sync time setting to 3 seconds. Then adjust the speed bias to bring the generator closer to the bus.
Test again. If the alarm persists, the PLL circuit may be faulty.
False sync (relay closes out of phase). Stop immediately. Verify phase rotation on both the generator and the bus. Tighten the sync window to ±5°.
Check the CT polarity. Never run a false sync test without a load bank or breaker protection.
Hunting after sync. The load signal is unstable. Check the CT wiring and polarity. Reduce the DROOP setting slightly.
If the hunting continues, replace the speed bias signal wiring with shielded cable.
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