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1. 50KV power supply When this unit fails it will leak a clear mineral oil stored inside, or cracking on the porcelain post will be visible, or a bulge in the side of the power supply will develop. Detection of a failed power supply will be noted when no high voltage is created. Usually, if there is no high voltage, there is some other issue causing the problem not the 50KV power supply. Check the 2-amp circuit breaker, capacitors, 1 Meg resistor, 20 Meg resistor, and 75-ohm resistors before replacing the power supply.

The porcelain posts of the power supply are very susceptible to surfacing tracking of electricity when they become dirty. Clean the porcelain posts with a clean dry rag (do not use solvents) regularly. Occasionally, if the porcelain posts are dirty, the operator may complain of a loud band. Usually, cleaning the porcelain posts will fix the complaint of a loud bang; however, the problem could be from an open 1 Meg or 20 Meg resistors.

Clean the entire high-voltage cabinet once a year minimally to ensure these issues do not develop into larger problems.

How to Clean the 50 KV Power Supply
Warning, always discharge voltages in the high-voltage cabinet before contact with the electronics. Although, the cabinet is designed to discharge the voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

2. 1 Meg and 20 Meg resistors. Both resistors are susceptible to damage if oil deposits from handling remain on the resistor. Therefore, after handling these resistors wipe the resistors with a clean dry rag (do not use a solvent) to remove oil deposits left from handling.

When standing in front of the high voltage cabinet, the 20 Meg is on the left, and the 1 Meg is mounted on the right. If there is no high voltage, measuring these two resistors is the second step in diagnosis of the problem. The first is to check the 2-amp breaker. It is important that 1 Meg and 20 Meg resistors be cleaned periodically to remove buffer dust and other dust that settles in the high voltage cabinet. Dust and debris that collects on the resistors can cause the resistors to fail and the electricity to surface track over the resistor. When the electricity surface tracks, the critical frequency is compromised, and the detector will not function optimally.

Clean the entire high voltage cabinet once a year, to ensure surface tracking of the electricity issues do not develop into larger problems. (When measuring the 1 Meg and 20 Meg resistors, ensure that the probe does not contact any part of the machine's structure. If the output wire, Key Chains, or Sidewall wires contact the structure of the NDT, a sneak path can cause an ohm measurement to be erroneous.)

Both the 1 Meg and 20 Meg resistors are mounted by with resistor bands and plastic standoffs. On older NDT machines, the resistor bands can fatigue and break. Additionally, the plastic standoffs become brittle and can break causing the resistors to hang by the wiring. This situation is dangerous and should be fixed immediately. Replacement of the entire resistor assembly is optimal. If only the bands and standoffs are replaced, ensure that the resistor functions properly by measuring each resistor with a multimeter.

Warning, always discharge voltages in the high-voltage cabinet before contact with the electronics. Although, the cabinet is designed to discharge the voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

3. Plexiglas plastic and resistor mounting.. The plastic is shaped and spaced to prevent surface tracking of the electricity. Occasionally, a resistor (1 Meg, 20 Meg, 5K Ohm, 150 Ohm, or 75 Ohm) will fail or other containments will collect on the Plexiglas or resistor mounting, which will cause surface tracking of the electricity. When this occurs, a carbon-mark may be seen on the Plexiglas or resistor mounting. If there are traces of carbon marks, which may look like melted or burnt spots, replace the plastic. If the plastic is not replaced, electricity will take the path of least resistance, and could surface track across the carbon mark even after the containments are cleaned or resistor is replaced. For example, if there is a burnt, carbon mark, or any damage to the Plexiglas or resistor mount replace those parts as well as remedy the reason for the occurrence of the mark. If only the cause of the carbon mark is replaced and not the plastic that retains the electrical carbon mark the problem will reoccur.

Warning, discharge voltages in the high-voltage cabinet before contact with the electronics; although, the cabinet is designed to discharge voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

4. Capacitors. The capacitors contain a clear mineral oil. Two capacitors are mounted is series with each other. When the capacitors are fully energized, a discharge from negative to positive occurs.

To verify the capacitor has failed check for leakage of the clear mineral oil, which is often difficult to see, or carbon markings or burning on the failed capacitor. To conclusively diagnosis a failed capacitor use a meter that is capable of checking capacitance.

Often when one of the capacitors fails the 2-amp circuit breaker, which protects the 50KV power supply will disengage. However, a disengaged 2-amp circuit breaker could be caused by a failed 1 Meg resistor, 20 Meg resistor, 50KV power supply, or even a bad 2-amp breaker.

Warning, discharge voltages in the high-voltage cabinet before contact with the electronic components; although, the cabinet is designed to discharge voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

5. Carbon Spheres. The carbon spheres thread onto the capacitors. When installing new carbon spheres use caution because the carbon material is much softer than the steel stud of the capacitor and the carbon spheres are susceptible to stripping of the treads if over tightened.

When standing if front of the high-voltage cabinet, the small carbon ball is on the left, and the large carbon sphere is mounted to the capacitor on the right.

The critical frequency is dependant on the gapping of the carbon spheres. The optimum gap is 11/16^th inch. However, depending on atmospheric conditions this distance could vary, but is should be insignificant, so once every 6 months gap the carbon spheres to 11/16^th inch. The reason for gapping the carbon spheres is that the carbon spheres wear due to heat. Because the spheres flatten, the spacing between the spheres widens causing the 11/16^th inch gap to increase.

If a flat spot grows to ½ inch in diameter, replace both the small and large carbon ball. When the carbon spheres gap increases so does the energy, hence the ability to arc to a flaw. However, the popping rate slows, which will decrease the inspection area of the tire. Additionally, any gap that varies from the 11/16^th inch will cause the critical frequency to change and cause the detector to function ineffectively.

Warning, discharge voltages in the high-voltage cabinet before contact with the electronics; although, the cabinet is designed to discharge voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

6. 75-Ohm resistors There are two 75-ohm resistors in the circuit used to create the voltage necessary to inspect steel belted tires.

If there is no high voltage when the Steel / Fabric selector is set to the steel position, measure these resistors to ensure that the circuit is good.

A by-product of high voltage is ozone. Occasionally, ozone will react with other chemicals to form new compounds. For example, compounds may form as liquids, or as corrosion, and will be visually apparent on many parts in the high voltage cabinet.

Cleans these resistors with a clean dry rag (do not use a solvent) once a year.

The two 75-ohm resistors are part of the circuit for fabric. The fabric circuit requires that both high voltage relays (relay #1 and relay #2) be in the open state. When high voltage relay #1 (the relay mounted to the left wall of the high voltage cabinet) is open, electricity is routed through the two 75-ohm resistors, through two 5-k ohm resistors, and then through two capacitors to complete the circuit.

When measuring resistors, ensure that the probe does not contact any part of the machine's structure, if the output wire, Key Chains, or Sidewall wires contact the structure of the NDT, a sneak path can cause an ohm measurement to be erroneous.

Warning, always discharge voltages in the high-voltage cabinet before contact with the electronics; although, the cabinet is designed to discharge the voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

7. 5 K Ohm resistors. These resistors are part of the circuit used to create the voltage necessary to inspect fabric belted tires.

If there is no high voltage when the Steel / Fabric selector is set to the Fabric position, measure the 5-K resistors to ensure that the circuit is good.

A by-product of high voltage is ozone. Occasionally, ozone will react with other chemicals to form new compounds. For example, compounds may form as liquids, or as corrosion and will be visually apparent on many of the parts in the high voltage cabinet.

Clean the 5 K ohm resistors with a clean dry rag (do not use a solvent) once a year.

The fabric circuit requires that both the high voltage relays (relay #1 and relay #2) be in the open state. When high voltage relay #1 (the relay mounted to the left wall of the high voltage cabinet) is open electricity is routed through two 75 ohm resistors, through two 5 k ohm resistors, and then through two capacitors to complete the circuit.

When measuring these resistors, ensure that the probe does not contact any part of the machine's structure, if the output wire, Key Chains, or Sidewall wires contact the structure of the NDT, a sneak path can cause an ohm measurement to be erroneous.

Warning, always discharge voltages in the high-voltage cabinet before contact with the electronics. Although, the cabinet is designed to discharge voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

8. 150 Ohm resistors. The 150-ohm resistors are output resistors. The resistor on the right, when standing in front of the high voltage cabinet, is used in the steel circuit only. Both resistors become a series of resistors, and are used for the fabric voltage circuit.

When the Steel / Fabric selector is positioned for steel voltage, and a flaw occurs in the tire, electricity is routed from the output of the capacitor, through high-voltage relay #2, through only one 150-ohm resistor; the 150 ohm resistor on the right; then out to the flaw. When the Steel / Fabric selector is positioned for fabric voltage, and a flaw occurs in the tire, electricity flows from the output of the capacitor, through the high-voltage coil, then through both 150-ohm resistors and out to the flaw.

A by-product of high voltage is ozone. Occasionally, ozone will react with other chemicals to form new compounds. For example, compounds may form as liquids or corrosion and will be visually apparent on these resistors. Clean these resistors with a clean dry rag (do not use a solvent) once a year.

When measuring these resistors, ensure that the probe does not contact any part of the machine's structure. If the output wire, Key Chains, or Sidewall wires contact the structure of the NDT, a sneak path can cause an ohm measurement to be erroneous.

Warning, discharge voltages in the high-voltage cabinet before contact with the electronics; although, the cabinet is designed to discharge the voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

9. High Voltage Relay #1 and #2. These relays are used to route electricity based on the Steel / Fabric selector. When the selector is positioned for steel voltage, both relays are in the closed position and the coils of the relays are not energized. When the selector is positioned for fabric voltage, both relays are in the open position and the coils of the relays are energized.

A by-product of high voltage is ozone. Occasionally, ozone will react with other chemicals to form new compounds. Compounds may form as liquids or as solids such as corrosion and will be visually apparent on the moving bus bar and fixed position contacts of the relay. Use emery cloth or a fine-grit sand paper to remove corrosion from the moving bus bar, and fixed position contacts once a year. Additionally, the metal block that slides back and forth in the coil of the relay tends to rust. The relays should be cycled periodically reduce seizure due to rust. If there is a lot of rust, the relay can be disassembled and the metal block that slides back and forth in the coil can be buffed clean.

Warning, discharge voltages in the high-voltage cabinet before contact with the electronics; although, the cabinet is designed to discharge voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

10. High-Voltage Coil. The 6 by 20 inch coil is used to increase the output voltage used for inspecting fabric tires. When measuring the coil it should read approximately 6-7 ohms.

Warning, discharge voltages in the high-voltage cabinet before contact with the electronics; although, the cabinet is designed to discharge the voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

10.5 High-voltage wiring Wires in the high-voltage cabinet are routed specifically to prevent surface tracking of the high-voltage electricity, and to ensure proper function of the NDT. When replacing wires, it is critical that the replacement wires match exactly with the factory routing. Some wires use plastic standoffs to ensure that the wire does not contact metal. Additionally, some wires carry positive voltages, and some carry negative voltages. If the routing of the positive and negative wires is too close to each other, arcing will occur.

11. Main disconnect and uses. The main disconnect and fuses act as a safety checkpoint. When the high voltage cabinet door is open, the red handle can be used for lockout tag out procedures. The red handle connects to a 12 inch shaft, which is connected to the mechanism that when in the off position disconnects line voltages from the main electronics.

There are two 15 amp slow blow fuses used in the disconnect. Both the line and neutral are fused. The main disconnect should be inspected once a year for excessive corrosion and replaced at the discretion of the inspecting technician. Additionally, if the red handle is damaged it should be replaced especially if the handle is cracked or allows debris in the cabinet.

Warning, discharge voltages in the high-voltage cabinet before contact with the electronics; although, the cabinet is designed to discharge the voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

12. Reset Relay This relay is used for safety. Three normally open contacts close when the operator presses the black reset button on the side of the high-voltage cabinet. If the NDT machine does not reset the three contacts should be checked for continuity.

Warning, discharge voltages in the high-voltage cabinet before contact with the electronics; although, the cabinet is designed to discharge the voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

13. Output – High-voltage Wire "The Antenna." The output high-voltage wire extends out from the 150-ohm output resistor in the high-voltage cabinet to the Master Square on the swing arm. The output wire is approximately eight feet long.

A by-product of high voltage is ozone, which causes the insulation of the wire to decay. When the cable begins to decay, or if the cable is placed within, close proximity to the metal, small pinholes will develop. When there is small pinhole in the wire, electricity can arc. When an arc occurs, the detector will recognize that there has been a change in the specific frequency and cause a flaw condition. The output high-voltage wire should be replaced at least once a year or more often. Replace the high-voltage output wire when the probe wire is replaced.

The output high-voltage wire terminates at the Master Square using a #10-ring terminal, spring and #10x3/8 inch stainless steel screw<. When replacing the high-voltage output wire on the NDT the #10-ring terminal, spring and #10x3/8 inch screw should be replaced. Do not use a screw longer than 3/8 inch when replacing the high-voltage output wire in the Master Square because there is a possibility that an arc will occur through the back of the square and cause a flaw condition.

Warning, discharge voltages in the high-voltage cabinet before contact with the electronics; although, the cabinet is designed to discharge the voltage, it is possible that voltages remain stored indefinitely. Ensure that all ground wires are in good condition during scheduled maintenance.

The Probe

14. Probe wire. The probe wire is approximately 26 inches long. The probe wire extends from the Slave Square to the K-Head Bar.

A by-product of high voltage is ozone, which causes the insulation of the wire to decay. When the cable begins to decay, or if the cable is placed within close proximity to metal, small pinholes will develop. When there is small pinhole in the wire, electricity can arc. When an arc occurs, the detector will recognize that there has been a change in the specific frequency and cause a flaw condition.

The probe wire should be replaced once a year or more often. Replace the probe wire when the high-voltage output wire is replaced. The probe wire is attached to the Slave Square by four 5/16 inch flat washers, and a 5/16x3/4 inch button head cap screw, and is attached to the K-Head Bar by a ¼-inch ring terminal. When installing this wire route the wire so it does not contact metal in any other location other than the K-Head Bar.

15. Paddles of the probe. There are different sizes of paddles used on various sized probes. The job of the paddle is to direct the Sidewall Wire when the probe is used to inspect a tire. If paddles are broken, they should be replaced.

16. Sidewall Wires and Key Chains. The Sidewall Wire and Key Chains expose the high voltage to a flaw. For the NDT to identify a flaw the Sidewall Wire or Key Chain must make affirmative contact with a flaw. If there is no contact between the Sidewall Wire, Key Chain, and Flaw there will be no arc, and no arc means no detection of the flaw.

Therefore, it is critical that the Sidewall Wires and Key Chains be replaced on a regular basis to ensure conformity. If the Sidewall Wires looses their ability to conform to the inside of the tire, replace them. If Key Chains are missing, broken, or just full of containments replace them.


17. Current Transformer The Current Transformer is mounted to the Mast of the Swing Arm on older NDT machines and to the side of the high-voltage cabinet on newer machines. When an arc occurs anywhere along the antenna the specific frequency changes, the current transformer intercepts the change in frequency, and sends it to the detector board via the coax cable.

A common service problem with the current transformer occurs when the little connector called the BnC connector breaks. With a broken BnC connector, the change in specific frequency that is intercepted by the Current Transformer cannot effectively be sent to the detector board, causing the NDT to miss flaws.

Typically, the Current Transformer does not go bad; however, there are cases where replacement of the Current Transformer is necessary. If the Current Transformer that is mounted to the Mast of the Swing Arm a Current Transformer Conversion Kit, must be installed.

18. Coax Cable

One end of the Coax Cable attaches to the BnC Connector on the Current Transformer, the other end connects to the BnC Connector on the detector circuit's enclosure. When the Current Transformer receives the specific frequency, the signal is sent through the coax cable to the detector circuit.

If the Coax Cable is not attached to either end, becomes damaged, or intercepts interference the detector board will not work properly.

Do not attach the Coax Cable to anything!! If the Coax Cable is attached to the high-voltage output wire the Coax Cable will intercept interference. The Coax Cable is very susceptible to interference, and interferences cause the detector to miss flaws.

There are a couple of different lengths of Coax Cables, which are based on the type of NDT machine. Older NDT-II and NDT-IIB machines use a 5'6" cable; INSP machines use a 7' cable (Hawkinson Part Number H02-0005), and Newer NDT-II, and NDT-2000 use 4' cables (Hawkinson Part Number H02-0003), and the Model 15-NDT uses a 3' cable. Use the right length cable to ensure the coax cable does not intercept interference.

19. Detector Board (Instructions to Conversion Kit for New Detector Board)



Detection of flaws by the NDT is accomplished by sensing a current change

If an arc occurs in the tire and the detector does not trigger a flawed condition there could be a number of possible reasons for this. However, the first step is to check the high voltage resistors, then the coax cable, current transformer, and its connectors. Read more….


Detector Board Outputs

(read more 1) Occasionally, due to atmospheric conditions, or variance in the input voltage of the NDT, the sensitivity of the Hawkinson Detector Board may need adjustment. (Old Board Adjustment, New Board Adjustment Read more….)

To adjust the sensitivity of older detector circuits

1. Set digital multimeter to DC volts
2. Connect the meter's DC negative to 12 Volts DC Negative (Use the black wire that is connected to the wiring harness of the new computer board.)
3. Connect the other meter lead to TP6
4. Adjust the potentiometer next to TP6. Turning the potentiometer counterclockwise increases the sensitivity. Turning the potentiometer clockwise decreases the sensitivity








To adjust the sensitivity of the new detector board follow these steps:

1. Set digital multimeter to DC volts
2. Connect the meter's DC negative to 12 Volts DC Negative (Use the black wire that is connected to the wiring harness of the new computer board.)
3. Connect the meter's DC positive to the left side of R13. R13 is a resistor located between R9 and R14. The left side of R13 is the side facing R9.
4. The factory setting should be 1.654 volts DC.
5. If the customer complains of missing flaws the sensitivity setting can be changed by adjusting the potentiometer R10 located directly above R13. Adjusting R10, by turning the screw counterclockwise will increase the sensitivity, and lower the DC volts displayed by the meter. Rotating the screw clockwise will decrease the sensitivity, and increase the the DC volts displayed by the meter. Settings of less than 1 VDC will typically be too sensitive, and trigger a flaw condition even if there is no flaw. Settings greater than 2 VDC will typically not be sensitive enough, and the detector will not trigger a flaw.

New Detector Circuit Adjustment Resistor and Potentiometer

(read more 2) In some cases the old detector circuit fails because one or more of the chips on the board fails. Replacement of the chips is an alternative to replacing the entire detector circuit board. However, most chips are difficult to source because the original equipment manufacturer no longer produces the chips.