The J 38792 Electronic Vibration Analyzer (EVA) is specifically designed to diagnose vibrations. This hand-held device is similar to a scan tool. A standard 12-volt power feed supplies the power. The vibration sensor, or the accelerometer, is at the end of a 6 mm (20 ft) cord. The vibration sensor can be mounted virtually anywhere on the vehicle where a vibration is felt.

EVA Basic Hookup

1. Verify that the software cartridge is correctly inserted at the bottom of the unit. (The cartridge usually remains there at all times.)
2. Connect the vibration sensor cord into either Input A or B.
3. Line up the sensor connector so that the release button is at the bottom.
4. Push the sensor connector into the input until the connector clicks and locks into place.
5. Plug the power cord into a 12-volt power feed in order to turn the EVA on. (The EVA is not equipped with an ON-OFF switch.)

To disconnect the sensor connector, press the release button and gently pull the connector straight out.

EVA Sensor Placement

Proper EVA sensor placement is critical in order to take proper vibration readings. You can place the sensor anywhere on the vehicle where vibrations are felt (1). Use putty or a hook and loop fastener in order to hold the sensor in place on non-ferrous surfaces, such as the surface of the steering column.

A magnet holds the sensor to ferrous surfaces.

Vibrations are typically felt in an up-and-down direction. The sensor is directionally sensitive. Therefore, place the sensor as flat as possible with the side marked UP facing upward. Place the UP side of the sensor in the exact position every time for consistent results when repeating the tests or making a comparison.

EVA Display

Up to three dominant vibration frequencies are displayed on the EVA's liquid crystal screen. On the left is the frequency reading, followed by a description of the vibration source. At the right side of the screen, the actual strength, or amplitude, is shown in acceleration force (G's).

Frequencies can be displayed in revolutions per minute (RPM) or in Hertz (Hz). Switch between the two readings by pressing the RPM/Hz button on the keypad.

Important: Verify that the letter on the display matches the correct sensor input.

Next to the frequency data on the top line of the screen is the letter A or B. This letter indicates which input is activated. Press the A/B button on the keypad in order to switch between the two inputs and set to the correct input that is being used.

The EVA offers the following main display features, all of which are described below:

Freeze

Pressing the FREEZE button on the keypad activates the freeze function, which locks the display of data. The display changes to Hz__FR_V = XX_______G and a caret symbol points to a vibration source. Additional diagnostic information or that vibration source can be viewed by pressing ENTER. The freeze function is useful when conducting an acceleration/deceleration test in which the significant amount of vibration registers only for a very short time. Pressing EXIT or the FREEZE button again deactivates the freeze function.

Record/Playback

The displayed vibration information can be recorded for later playback. The EVA retains stored data for approximately 70 hours after the unit has been unplugged from a power source. Data is recorded as snapshots of vibration information. Each snapshot consists of 10 different frames. Up to 10 snapshots can be recorded.

Press the RECORD button in order to record a snapshot. The screen will display R? in order to request a tag number between 0 and 9. These tag numbers are the individual frames of the snapshot recording. Then press ENTER to begin recording. New data will replace the existing data when a number is chosen that has already been used in order to tag a snapshot.

Pressing the PLAYBACK button plays back the recorded data. The screen shows P? in order to request the tag number for the wanted snapshot. Once the number is entered, the snapshot data displays the letter P followed by the tag number then press ENTER to play back the data. Then the screen displays the letter F followed by a number between 0 and 9 in order to indicate which frame of the snapshot is being displayed.

Use the freeze function in order to freeze the display at any point in the sequence during playback. You can view individual frames in a forward or backward sequence using the UP and DOWN arrow keys.

The display returns to the active screen when the recording or playback of a snapshot is finished, or when EXIT is pressed.

Averaging/Non-Averaging Modes

The EVA normally operates in an averaging mode that averages multiple vibration samples over a period of time. The averaging mode minimizes the effects of a sudden vibration that is not related to the problem (such as from potholes or from uneven road surfaces). Most tests use the averaging mode.

The EVA is more sensitive to vibrations in the non-averaging mode. The display is more instantaneous and not averaged over a period of time. The non-averaging mode is used when measuring a vibration that exists for only a short period of time, and during acceleration/deceleration tests.

Pressing the AVG button switches between the averaging and non-averaging modes. During the averaging mode, the screen will display AA. During the instantaneous mode the top of the screen will display IA.

Strobe Balancing

The J 38792 can strobe balance a rotating component. A trigger wire is located on the top of the EVA, which is used with an inductive pick-up strobe light (timing light). The EVA triggers the strobe light at the same frequency as the most predominant vibration. The timing light clips on to the trigger wire. The vibration sensor must be attached to input A. Input B does not provide the strobe function.

Pressing the STROBE button starts the strobe balancing function. The EVA will ask a series of questions in order to determine the correct filter range: low, medium or high.

The low, medium and high ranges prevent other vibrations from interfering with the operation of the strobe light. Press YES in order to select a range. Press NO in order to go on to the next range. The vibration/strobe frequency must fall within the selected range.

The EVA will display the signal frequency, signal level (amplitude), and filter range. The EVA is now ready to begin the strobe balance procedure.

Auto Mode

Auto Mode considers the suspected source of vibration in conjunction with the vehicle's baseline data to identify a suspected source of vibration.

1. Select AUTO MODE from the EVA main menu. The EVA will ask to select the suspected source of vibration as ENGINE RPM or VEHICLE SPEED.

•	If engine RPM is selected, move the cursor to the correct number of engine cylinders then press ENTER. Using the EVA keypad, enter the engine RPM (500-6000 RPM) where the vibration occurs at a maximum level.

•	If vehicle speed is selected, enter the tire size information with one of the following three options:

-	RPS at 5 mph -- Look up the revolutions per second (RPS) for specific tire size.

-	Database -- Select tire type and tire size from each selection screen.

-	Manual Entry -- Select Manual Entry when the vehicle is fitted with specialty tires.

2. Enter one of the following driveshaft configurations:

•	FWD (Front Wheel Drive)

•	RWD (Rear Wheel Drive)

•	AWD (All Wheel Drive)

•	4WD (Four Wheel Drive)

3. Enter the axle ratio only if FWD is not selected.
4. Select the vehicle speed units in mph (miles per hour) or km/h (kilometers per hour).

Smart Strobe

The Smart Strobe mode enables complete control of the frequency at which the strobe light will flash. Smart Strobe is well suited for identifying the speed at which objects are rotating at. This is helpful for identifying the source of a vibration. The pulley RPM can be converted to a frequency by pressing the RPM/Hz key.

1. To use the Smart Strobe function, begin by clipping the inductive pickup of the timing light to the wiring loop of the EVA.
2. Connect to a 12-volt power source.
3. If a timing light with an advance feature is used, set advance to 0 degrees.
4. From the Main Menu, select Smart Strobe.
5. With the engine off, mark the object you suspect is causing vibration. A dab of white paint or correction fluid works well.
6. Enter an initial test point strobe frequency between 10-200 Hz (600-12000 RPM).
7. Run the engine at the RPM at which the vibration is the greatest and trigger the strobe.
8. As you point the strobe light at the spinning object, press the Strobe Light trigger.
9. Press the EVA up or down keys to manually adjust the strobe speed until only one mark is seen and the mark on the object appears stationary.
10. As the test is run, the strobe speed must be manually adjusted to match the actual object RPM.

EVA Calibration

The EVA features the following two built-in calibration procedures:

Calibrate a replaced or an added sensor in order to function properly with the EVA unit. The phase shift calibration is performed at the factory. Do NOT repeat this calibration under normal use.

Sensor Calibration

1. Lay the sensor on a flat stationary surface with the UP side facing upward.
2. Plug the sensor into either input A or B.
3. Plug the EVA into a 12-volt power supply.
4. After the display initializes, select the proper input.
5. Press the number 1 to initiate sensor calibration.
6. Press the number 2 three times on the keypad. The message BURNING will appear, followed by a request to turn the sensor over.
7. Turn the sensor over.
8. Press any key in order to commence calibration:

•	Calibration will take approximately 20 seconds.

•	The display will return to the active mode when calibration is complete.

Phase Shift Calibration

1. Plug the EVA into a 12-volt power supply.
2. Press the number 5 to initiate phase shift calibration.
3. Press the number 2 on the keypad three times in order to begin calibration:

•	Do not press any key until the message ANY KEY TO CONTINUE appears. Pressing a key will cancel the calibration process.

•	The display will flash numbers for 5-6 minutes. (If the numbers flash for more than 10 minutes, the EVA is defective.)

•	The message BURNING PHASE SHIFT CONSTANTS will appear for one minute.

•	The BURNING CENTER FREQUENCIES LOW=40, MEDIUM=50, HIGH=60 message will appear.

•	The ANY KEY TO CONTINUE message should appear.

4. Press any key in order to return to the active mode.

Keypad Reference

A/B: Switches the display between the A Input and the B Input. You must use Input A when strobe balancing.

AVG: Switches the display between the non-averaging mode and the averaging mode. The non-averaging mode is more sensitive to sudden vibration variations. When in the averaging mode, the word AVG appears at the top of the display.

RPM/HZ: Switches the frequency display between RPM and Hz.

FREEZE: Locks the display data at that moment and displays the word FRZ at the top of the screen. This key operates in the active display or during playback. Pressing the FREEZE key again or pressing the EXIT key unlocks the display.

RECORD: Places the EVA in the record mode. Pressing the EXIT key will return the screen to the active display.

PLAYBACK: Places the EVA in the playback mode in order to view vibration information that was previously recorded. Pressing the EXIT key will return the key screen to the active display.

Numeric Keys (0-9): The numbered keys are used in order to select one of ten snapshot tag numbers between 0 and 9 when recording or playing back information.

Arrow Keys: The arrow keys are used in order to move through the individual frames of a snapshot during a freeze in the playback mode. Pressing the UP arrow moves forward one frame and pressing the DOWN arrow moves backward one frame.

ENTER: Once the EVA is in the record mode and you have selected a snapshot tag number, press ENTER in order to start recording.

STROBE: Places the EVA in the strobe mode for driveshaft balancing and diagnosis. Pressing the EXIT key will return the screen to the active display.

YES and NO: Used in order to select a filter range when in the strobe balancing mode.

EXIT: Returns the screen to the active display when the EVA is in the freeze mode, the record mode, the playback mode, or the strobe mode.