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The HD90 MKIV and Its Role in Rock Drilling
The HD90 MKIV drill rig is a mid-sized hydraulic crawler drill designed for rock processing, quarrying, and site preparation. Manufactured during the late 20th century by a specialized equipment firm focused on hard rock applications, the HD90 series became known for its mechanical reliability and modular design. The MKIV variant introduced refinements in engine control, fuel delivery, and electrical integration, making it a popular choice for small rock processing companies and independent contractors.
While exact production numbers are difficult to trace, the HD90 MKIV was widely distributed across North America and parts of Asia, often used in tandem with crushers and conveyors. Its diesel engine, typically a Perkins or Deutz model, powers both the hydraulic system and auxiliary electrical components, including the fuel lift pump, hour meter, and safety interlocks.
Symptoms of Electrical Failure
A common issue with the HD90 MKIV is engine non-start due to electrical faults. In one case, the hour meter failed to activate, which in turn prevented the fuel lift relay from energizing. Without fuel delivery, the engine remains starved and cannot start. Operators often resort to manually jumping power to the fuel pump and solenoid to bypass the control circuit.
Additional symptoms include:
Key Components and Their Functions
To resolve electrical startup issues:
Field Anecdotes and Lessons Learned
One mechanic in Arizona spent dozens of hours diagnosing a non-start issue, only to discover that a failed temperature switch was grounding the solenoid circuit. Another technician found that the hour meter had internally shorted, preventing the fuel relay from activating. After replacing the meter and cleaning all terminals, the rig started reliably.
In a 2017 incident at a quarry in Nevada, an HD90 MKIV failed to start during a critical blasting prep. The crew bypassed the fuel pump circuit using jumper wires and completed the job, but later installed a new relay and rewired the safety interlocks to prevent recurrence.
Conclusion
Electrical faults in the HD90 MKIV drill rig often stem from interdependent components like the hour meter, fuel relay, solenoid, and temperature switch. Understanding the control logic and tracing each circuit methodically is key to restoring functionality. With proper diagnostics and targeted repairs, even complex wiring issues can be resolved without excessive parts replacement. The HD90 MKIV remains a capable and serviceable rig for rock processing operations.
The HD90 MKIV drill rig is a mid-sized hydraulic crawler drill designed for rock processing, quarrying, and site preparation. Manufactured during the late 20th century by a specialized equipment firm focused on hard rock applications, the HD90 series became known for its mechanical reliability and modular design. The MKIV variant introduced refinements in engine control, fuel delivery, and electrical integration, making it a popular choice for small rock processing companies and independent contractors.
While exact production numbers are difficult to trace, the HD90 MKIV was widely distributed across North America and parts of Asia, often used in tandem with crushers and conveyors. Its diesel engine, typically a Perkins or Deutz model, powers both the hydraulic system and auxiliary electrical components, including the fuel lift pump, hour meter, and safety interlocks.
Symptoms of Electrical Failure
A common issue with the HD90 MKIV is engine non-start due to electrical faults. In one case, the hour meter failed to activate, which in turn prevented the fuel lift relay from energizing. Without fuel delivery, the engine remains starved and cannot start. Operators often resort to manually jumping power to the fuel pump and solenoid to bypass the control circuit.
Additional symptoms include:
- No response from the fuel pump when ignition is turned on
- A solenoid mounted beneath the injector pump failing to engage
- A temperature switch on the engine’s left side interfering with solenoid operation
- Missing or non-functional horn switch wired into the emergency shutoff system
Key Components and Their Functions
- Hour Meter Relay
Acts as a trigger for the fuel lift relay. If the hour meter fails, the relay may not energize, cutting off fuel delivery.
- Fuel Lift Relay
Controls power to the fuel pump. It depends on signals from the hour meter and ignition circuit.
- Solenoid on Injector Pump
Shuts off fuel flow when de-energized. It may be wired through a temperature or oil pressure switch.
- Temperature Switch
Serves as a safety interlock. If the engine overheats, it disables the solenoid to prevent damage.
- Horn and Emergency Shutoff Circuit
In some configurations, the horn switch is wired into the emergency shutoff. A missing horn switch can break the circuit, disabling the rig.
- Fuel Lift Pump: A low-pressure pump that delivers fuel from the tank to the injector system.
- Solenoid: An electromechanical device that controls fluid or fuel flow via magnetic actuation.
- Interlock Circuit: A safety system that prevents operation unless certain conditions are met.
- Jumping Power: Manually connecting power to a component to bypass its control circuit.
To resolve electrical startup issues:
- Test the hour meter circuit for continuity and voltage. Replace the meter if it fails to trigger the relay.
- Inspect the fuel lift relay and verify it receives signal from the hour meter and ignition switch.
- Check the solenoid wiring for corrosion or loose connections. Confirm voltage at the solenoid when ignition is on.
- Bypass the temperature switch temporarily to test solenoid function. Replace the switch if faulty.
- Verify the horn switch circuit and install a jumper if the switch is missing.
Field Anecdotes and Lessons Learned
One mechanic in Arizona spent dozens of hours diagnosing a non-start issue, only to discover that a failed temperature switch was grounding the solenoid circuit. Another technician found that the hour meter had internally shorted, preventing the fuel relay from activating. After replacing the meter and cleaning all terminals, the rig started reliably.
In a 2017 incident at a quarry in Nevada, an HD90 MKIV failed to start during a critical blasting prep. The crew bypassed the fuel pump circuit using jumper wires and completed the job, but later installed a new relay and rewired the safety interlocks to prevent recurrence.
Conclusion
Electrical faults in the HD90 MKIV drill rig often stem from interdependent components like the hour meter, fuel relay, solenoid, and temperature switch. Understanding the control logic and tracing each circuit methodically is key to restoring functionality. With proper diagnostics and targeted repairs, even complex wiring issues can be resolved without excessive parts replacement. The HD90 MKIV remains a capable and serviceable rig for rock processing operations.
