Symptom → suspect module → part number. Gate firing pulse failures, misfires, one leg dead, phase loss, assignment dropout, autosync hunt — start from what the drive is doing and work back to the board.
Independent sourcing, not an authorized distributor. Ross Hill, NOV, and other manufacturer names and part numbers are used for reference only. This page is a diagnostic starting point written from our sourcing records — it is not a substitute for a qualified rig electrician working at the equipment.
Start from the symptom, not the part number: SCR gate firing, drive assignment, and protection live on the AC control module; DC motor field and regulation live on the DC control modules; and one-leg-dead or repeated fuse loss points at the bridge or phase cells for that bay. Most people troubleshooting a Ross Hill / NOV SCR house reach it from what the drive is doing. The table maps the common failure signatures to the module families and the part pages that cover them.
| What you are seeing | What it usually indicates | Suspect module / part pages |
|---|---|---|
| No gate firing pulses, or a gate firing pulse failure alarm on one drive | The AC control module owns SCR gate firing, drive assignment, and protection. Verify supply voltages at the card before condemning it. | 0521-2500 AC control module (RHCC) — family incl. 0521-2500-14 · 0521-2500-32 |
| Firing pulses missing or erratic on one bridge leg — one leg dead, an SCR not firing | Either the firing signal path on the AC module or the power section itself. On a Model 1400 bay that is the SCR bridge; on a Model 1500 it is the phase cells. Verify the generation first — they are not interchangeable. | 0001-6307-70 Model 1400 SCR bridge · 0100-0150-03 Model 1500 phase cell |
| Drive misfiring under load — unbalanced output, unstable DC under load | A misfire on one leg unbalances the DC output. Check the bay’s semiconductor fuses, then the bridge or phase cells for that bay, then the firing circuit on the AC module. | Same parts as one-leg-dead above, plus SCR bay components |
| Repeated semiconductor fuse loss on one bay | A fuse that keeps clearing is protecting something — usually a failing SCR device in the bridge or phase cell rather than a bad batch of fuses. | Model 1400 bridge · Model 1500 phase cell · Power modules |
| Phase loss at a bay — one incoming leg dead ahead of the bridge | Rule out the supply side before touching modules: incoming connections and the bay’s semiconductor fuses first. A lost input phase mimics a dead bridge leg from the output side. | SCR bay components, then bridge / phase cell per generation |
| Drive assignment dropout — mud pump, drawworks, or rotary table will not take or hold assignment | Drive assignment lives on the AC control module alongside firing and protection. If an otherwise identical set behaves differently, compare dash suffixes between the two before swapping boards. | AC control module — 0521-2500 family |
| No field or weak field on a DC drilling motor | The DC control module regulates the motor field — and the shunt type and series type are different variants matched to different motor fields. Confirm the field configuration from the motor, not the drawing. The field supply PCB is the other suspect. | 0522-2400-00 shunt · 0522-2400-27 series · 0509-1300 field supply PCB |
| Speed will not follow the driller’s handwheel setpoint; hunting or poor regulation | The regulation variant of the DC module sets SCR phase angle from the handwheel setpoint. Reseat first — a fault that clears on reseat and returns usually points at the card-edge connector or backplane, not the card. | 0522-2400-23 DC module, regulation · 0522-2400-21 (NOV 6415-2400-21) |
| Generator will not synchronise, or autosync hunts without locking in | The AutoSync module — but on this family the dash suffix is an engine calibration, not a revision. The wrong calibration will not sync even on a healthy module. Match the suffix to the engine before replacing anything. | 0000-8500-00 · 0000-8500-18 calibrated variant |
| Bay or module overheating; thermal trips during heavy drilling | Cooling before electronics: blowers, filters, and airflow paths. The Model 1400 blower is a 2 HP 600 V 3-phase unit cooling the SCR bay and modules. | 0002-1076-62 Model 1400 blower · SCR bay components |
| Weak or absent drawworks dynamic braking | Two different items get confused here: the DWDB grid resistor assembly and the NOV dynamic brake resistor bank. They are not the same part — send the number on your unit. | 0100-1000-04 DWDB grid resistor · 10509209-001 resistor bank |
| DC contactor not pulling in, chattering, or welded | The Eaton 6702ED584 and the Ross Hill 0100-0389-02 share the same 1800 A / 74 VDC headline rating and are different parts — do not treat them as interchangeable, and note that coil voltage varies by suffix. | 6702ED584 (74 VDC coil) · 6702ED584-2 (115 VDC coil) · 0100-0389-02 |
| Fault clears when you reseat the card, then returns | Card-edge connector or backplane rather than the card itself. Swapping boards into a bad slot condemns good spares one at a time. | SCR house parts — and describe the slot behaviour when you contact us |
| Replacement module physically fits but does not function correctly | Wrong variant for the configuration. Across these families the dash suffix can mean a frequency, an engine calibration, a motor field configuration, or a coil voltage. Mechanical fit proves nothing. | Ross Hill / NOV cross-reference — check the dash number against your set |
| The number on the board returns nothing anywhere you search | Before concluding a part is unobtainable, check whether the number is one of the known discrepancies in this equipment. Several numbers are recorded two ways — a transposed prefix group or a different middle group — and a search against one form returns nothing while the other form is available. | 0521-2400-21 vs 0522-2400-21 · 0522-2400-00 vs 0522-2500-00 · full cross-reference |
Reference only. These are starting points for diagnosis, not a substitute for it — and the nameplate outranks every list, including ours.
Verify the cheap and reversible things first: supply voltages at the card, semiconductor fuses, connector seating, and the dash suffix on the module — in that order. The pattern behind most wasted spares is condemning a board that was never the fault: a bad backplane slot, a lost input phase, or a variant mismatch will all imitate a failed module. When the same fault follows the slot rather than the card, stop swapping boards.
The 0509-series boards split the control work by function — console, field supply, hoisting protection, power limit, and excitation — while the 0000-8500 AutoSync family handles generator synchronising. If the symptom is confined to one function, start at that board’s page.
| Part number | Board | Function |
|---|---|---|
0509-2500 | Driller’s console PCB (PC1) | Driller’s console interface |
0509-1300 | Field supply PCB | DC motor field supply |
0509-2600 | Sprocket slip PCB | Protection function on hoisting equipment; single-phase |
0509-7497 | Power limit controller PCB | Power limit function |
0509-7901 | Generator exciter PCB | Generator excitation |
0000-8500-00 | AutoSync AC II module | Generator synchronising |
No — Model 1400 and Model 1500 power-section components are not interchangeable, and phase cells are the textbook case. Before ordering a bridge, phase cell, or blower, confirm which generation the house is. A board that fits the rack is not evidence that it matches your set: across these families a dash suffix can mean a frequency, an engine calibration, a motor field configuration, or a coil voltage.
Condition always disclosed before sale. Photos on request. Same-day response on most requests.
Same-day response on most requests. Condition disclosed before sale.