Eagle FISHMARK 640C Installation And Operation Instructions Manual

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[Page 1] Eagle FISHMARK 640C

Pub. 988-0143-861 www.eaglesonar.com Fish-Finding & Depth-Sounding Sonars Installation and Operation Instructions ...

[Page 2] Eagle FISHMARK 640C

Copyright © 2005 LEI-Eagle All rights reserved. Eagle ® , FishMark ® and SeaFinder ® are registered trademarks of LEI No part of this manual may be copied, reproduced, republished, transmitted or distributed for any purpose, without prior writt...

[Page 3] Eagle FISHMARK 640C

i Table of Contents Read Me First!...................................................................................1 Capabilities and Specifications: FishMark ® 640c ..............................2 SeaFinder ® 640c DF..............................

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ii Main Menu .........................................................................................39 Pages ..................................................................................................40 Basic Sonar Quick Reference .............

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iii To turn off HyperScroll..................................................................74 Pop-up Help........................................................................................74 Reset Options .........................................

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iv Notes ...

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1 Section 1: Read Me First! How this manual can get you out on the water, fast! Welcome to the exciting world of digital sonar! We know you're anxious to begin finding fish, but we have a favor to ask. Before you grab your unit and begin install...

[Page 8] Eagle FISHMARK 640C

2 any longer, turn to the Quick Reference on page 45 and head for the water with your sonar unit!) After you have gained some experience with your sonar, you'll want to check out Section 4, which explains more advanced Sonar Options and Other Fe...

[Page 9] Eagle FISHMARK 640C

3 Back-up memory: .......... Built-in memory stores sonar settings for decades. Languages:...................... 10; menu languages selectable by user. Sonar Frequency:...................... 50/200 kHz for SeaFinder 640c DF; 200 kHz for FishMark 640c...

[Page 10] Eagle FISHMARK 640C

4 Surface water temp: ..... Yes. Speed/distance log: ....... Optional (requires optional speed sensor). NOTICE! The storage temperature range for your unit is from -4 degrees to +167 degrees Fahrenheit (-20 degrees to +75 degrees Celsius). Ex- tended...

[Page 11] Eagle FISHMARK 640C

5 How to Use this Manual: Typographical Conventions Many instructions are listed as numbered steps. The keypad and arrow "keystrokes" appear as boldface type. So, if you're in a real hurry (or just need a reminder), you can skim the in...

[Page 12] Eagle FISHMARK 640C

6 For example, instructions for turning on the Fish ID feature would look like this: 1. From the Sonar Page, press MENU|↓ to SONAR FEATURES|ENT. 2. Press → or → ↓ to FISH ID SYMBOLS|ENT|EXIT|EXIT. Translated into complete English, step 1...

[Page 13] Eagle FISHMARK 640C

7 Section 2: Installation & Accessories Preparations You can install the sonar system in some other order if you prefer, but we recommend this installation sequence: Caution: You should read over this entire installation section before drill- ing...

[Page 14] Eagle FISHMARK 640C

8 adjustable strap. These are "kick-up" mounting brackets. They help prevent damage if the transducer strikes an object while the boat is moving. If the transducer does "kick-up" the bracket can easily be pushed back into place wi...

[Page 15] Eagle FISHMARK 640C

9 grit sandpaper, specially formulated epoxy adhesive available from LEI (see ordering information on the inside portion of the back cover). A sandwich hull also requires polyester resin. Selecting a Transducer Location 1. The location must be in the...

[Page 16] Eagle FISHMARK 640C

10 5. If possible, route the transducer cable away from other wiring on the boat. Electrical noise from engine wiring, bilge pumps and aerators can be displayed on the sonar's screen. Use caution when routing the trans- ducer cable around these ...

[Page 17] Eagle FISHMARK 640C

11 However, there are times when you may need to adjust the transducer slightly higher or lower. The slots in the mounting brackets allow you to loosen the screws and slide the transducer up or down. If you fre- quently lose bottom signal lock while ...

[Page 18] Eagle FISHMARK 640C

12 Lack of angle adjustment can be particularly troublesome on hulls that sit with the bow high when at rest or at slow trolling speeds. Third, a transducer CAN NOT shoot through wood and metal hulls. Those hulls require either a transom mount or a t...

[Page 19] Eagle FISHMARK 640C

13 Align plastic ratchets in bracket. B. Two-piece bracket: Locate the four plastic ratchets in the trans- ducer's hardware package. Press two ratchets into the sides of the plastic bracket and two on either side of the transducer as shown in t...

[Page 20] Eagle FISHMARK 640C

14 Add ratchets to bracket and transducer. 2. Aligning the transducer on the transom. A. One-piece bracket: Slide the transducer between the two ratch- ets. Temporarily slide the bolt though the transducer assembly and hold it against the transom. Lo...

[Page 21] Eagle FISHMARK 640C

15 Insert bolt and check transducer position on transom. B. Two-piece bracket: Assemble the transducer and bracket as shown in the following figure. Temporarily slide the bolt though the transducer assembly but don't tighten the nut at this time...

[Page 22] Eagle FISHMARK 640C

16 Assemble transducer and bracket. 3. Assembling the transducer. A. One-piece bracket: Once you determine the correct position for the ratchets, assemble the transducer as shown in the following figure. Don't tighten the lock nut at this time. ...

[Page 23] Eagle FISHMARK 640C

17 Mark the center of each slot for the mounting screw pilot holes. You will drill one hole in the center of each slot. Drill the holes. For the one-piece bracket, use the #29 bit (for the #10 screws). For the two-piece bracket, use the #20 bit (for ...

[Page 24] Eagle FISHMARK 640C

18 tighten the lock nut! If you do, the transducer won't "kick-up" if it strikes an object in the water. Align transducer centerline with hull bottom and attach transducer to transom. Rear view of dual-frequency Skimmer shown. 6...

[Page 25] Eagle FISHMARK 640C

19 Caution: If you drill a hole in the transom for the cable, make sure it is lo- cated above the waterline. After installation, be sure to seal the hole with the same marine grade above- or below-waterline seal- ant used for the mounting screws. 7. ...

[Page 26] Eagle FISHMARK 640C

20 Transducer mounted on trolling motor, side view. Transducer Orientation and Fish Arches If you do not get good fish arches on your display, it could be because the transducer is not parallel with the ground when the boat is at rest in the water or...

[Page 27] Eagle FISHMARK 640C

21 If the arch slopes up – but not back down – then the front of the trans- ducer is too high and needs to be lowered. If only the back half of the arch is printed, then the nose of the transducer is angled too far down and needs to be raised. NO...

[Page 28] Eagle FISHMARK 640C

22 For example, some (but not all) manufacturers use a layer of fiberglass, then a core of balsa wood, finishing with an outer layer of fiberglass. Re- moving the inner layer of fiberglass and the balsa wood core exposes the outer layer of fiberglass...

[Page 29] Eagle FISHMARK 640C

23 harder (more rocky) the bottom, the easier it will be to get a second bot- tom signal. Don't touch the controls once they've been set. Example of a second bottom signal. Unit is in 30 feet of water, with range set at 80 feet and sensitiv...

[Page 30] Eagle FISHMARK 640C

24 4. Most people can get good results by following steps 1 through 3, so this step is optional. If you want to make an extra effort to be absolutely sure that your selected location will work under all conditions, make a test run with the boat on pl...

[Page 31] Eagle FISHMARK 640C

25 Epoxy transducer to hull. WARNING: Use only the epoxy available from LEI. It has been for- mulated to work with these installation procedures. Other epoxy types may be too thin or may not cure to the right consistency for optimum transducer perfo...

[Page 32] Eagle FISHMARK 640C

26 3. Press the transducer into the epoxy, twisting and turning it to force any air bubbles out from under the transducer face. Stop pressing when you bottom out on the hull. When you're finished, the face of the trans- ducer should be parallel ...

[Page 33] Eagle FISHMARK 640C

27 Sonar unit with external temp sensor, external speed sensor, or combo speed/temp sensor. The primary temperature sensor is built into the transducer. Optional Speed Sensor Installation All the units in this series can display speed and distance tr...

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28 Recommended tools for this job include: drill, 5/8" drill bit, 1/8" drill bit for pilot holes, screwdriver. Required supplies for this job include: four #8 stainless steel wood screws (3/4" long), high quality, marine grade above- o...

[Page 35] Eagle FISHMARK 640C

29 Speed sensor mounting configuration: side view (left) and rear view (right.) Route the sensor's cable through or over the transom to the sonar unit. If you need to drill a hole in the transom to pass the connector through, the required ho...

[Page 36] Eagle FISHMARK 640C

30 Caution: When using the unit in a saltwater environment, we strongly rec- ommend that you shut off the power supply to the power cable when the unit is not in use. When the unit is turned off but still connected to a power supply, electrolysis can...

[Page 37] Eagle FISHMARK 640C

31 Power connections for the sonar unit. WARNING: Do not use this product without a 3-amp fuse wired into the power cable! Failure to use a 3-amp fuse will void your warranty. This product must be independently fused with the enclosed 3-amp fuse (or ...

[Page 38] Eagle FISHMARK 640C

32 Bracket Installation Mount the unit in any convenient location, provided there is clearance behind the unit when it's tilted for the best viewing angle. You should also make sure there is enough room behind the unit to attach the power and tr...

[Page 39] Eagle FISHMARK 640C

33 sure to leave enough slack in the cables to allow tilting or swiveling the unit. If you choose to fill in the hole, be sure to position the cables against the rear edge of the hole as you apply the fill material. Front view (left) and side view (r...

[Page 40] Eagle FISHMARK 640C

34 In-Dash Installation You can mount the unit in the dash with an optional FM-5 In-Dash Adapter Kit. The kit includes mounting hardware, a template for cut- ting the hole and an instruction sheet, part 988-0147-43. In-dash mounting template...

[Page 41] Eagle FISHMARK 640C

35 The portable power pack can be used with eight "D" cell alkaline bat- teries or an optional sealed, rechargeable battery. For set-up directions, refer to the pack's instruction sheet. Install batteries in power pack battery adapter....

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36 Notes ...

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37 Basic Sonar Operation This section addresses the unit's most basic sonar operations. The in- structions presented in Sec. 3 follow a chronological order. Sec. 4, Sonar Options & Other Features, will discuss the more advanced functions an...

[Page 44] Eagle FISHMARK 640C

38 1. PWR/LIGHT (Power & Light) – The PWR key turns the unit on and off and controls the backlight level. 2. PAGES – Pressing this and the ↑ and ↓ arrow keys switches the unit between the three different page display options. (Full Sonar ...

[Page 45] Eagle FISHMARK 640C

39 Turn off the unit by pressing and holding the PWR key for 3 seconds. Main Menu The unit has a Main Menu which contains both function and setup op- tion commands. The instructions in this section will deal with sonar functions, the basic commands ...

[Page 46] Eagle FISHMARK 640C

40 The Main Menu commands and their functions: Screen command changes the contrast, brightness or display mode. Sounds command enables or disables the sound, set the volume or set the alarm style. Transparency command adjusts the level of transparenc...

[Page 47] Eagle FISHMARK 640C

41 Pages Menu showing Sonar display options. All of the display options show the sonar chart in some format. This is a "cross-section" view of the water column beneath the boat. The chart moves across the screen, displaying sonar signal ech...

[Page 48] Eagle FISHMARK 640C

42 Sonar page in Split Zoom Sonar Chart display mode. Sonar page in Digital Data display mode. ...

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43 Sonar Page Menu. Most of these functions are discussed in Sec. 4. The Sonar Page has its own menu which is used for some advanced func- tions and for setting various options. Sonar Options and other features are discussed in Sec. 4. To access the ...

[Page 50] Eagle FISHMARK 640C

44 Sonar Page showing full sonar chart mode. Surface clutter Bottom signal Fish arches In FasTrack, fish arches show as horizontal bars. Depth scale Digital data overlay (depth & temperature) Surface signal ...

[Page 51] Eagle FISHMARK 640C

45 Basic Sonar Quick Reference 1. Mount the transducer and unit. Connect the unit to electric power and the transducer. 2. Launch your boat. 3. To turn the unit on press and release the PWR key. 4. Head for your fishing spot. The unit should automat...

[Page 52] Eagle FISHMARK 640C

46 depth appears in a box at the right end of the cursor line. To clear the cursor, press EXIT. 9. If you are drifting at a very low speed or anchored, you are not mov- ing fast enough for a fish to return the tell-tale fish arch signal. As you drif...

[Page 53] Eagle FISHMARK 640C

47 These figures show results of different sensitivity levels on the same lo- cation. Fig. 1: Sensitivity at 88 percent, determined by Auto Sensitivity. Typical of full auto mode. Fig. 2: Sensitivity set at 75 percent. Fig...

[Page 54] Eagle FISHMARK 640C

48 Adjusting sensitivity in Auto Sensitivity Mode is similar to manually adjusting a car's speed with the accelerator pedal while cruise control is on. You can tell the car to run faster, but when you let off the gas the cruise control automatic...

[Page 55] Eagle FISHMARK 640C

49 Sonar Menu (left) with Sensitivity command selected. The Sensitivity Control Bar is shown at right. NOTE: If you want to change the sensitivity in Manual Mode, first turn off Auto Sensitivity. From the Sonar Page press MENU|↓ to AU...

[Page 56] Eagle FISHMARK 640C

50 Fish Symbols vs. Full Sonar Chart You may have noticed in the quick reference we used fish arches in full sonar chart mode for our example instead of the popular Fish I.D. fish symbol feature. Here's why. Fish I.D. is an easier way for a s...

[Page 57] Eagle FISHMARK 640C

51 For the ultimate training aid download the free emulator software for your unit. Aside from being just plain fun, this program can help you learn both basic and advanced operations without burning boat fuel. Eagle is one of the first sonar manufac...

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52 Notes ...

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53 Section 4: Sonar Options & Other Features Material in this section is arranged in alphabetical order. ASP (Advanced Signal Processing) The ASP feature is a noise rejection system built into the sonar unit that constantly evaluates the ef...

[Page 60] Eagle FISHMARK 640C

54 Sonar Menu (left) with Sonar Features selected. In the Sonar Features menu (center) the SeaFinder's Noise Rejection feature is se- lected with ASP in the default low setting. The Noise Rejection feature (far right) is set the same in the...

[Page 61] Eagle FISHMARK 640C

55 Depth Alarms The depth alarms sound a tone when the bottom signal goes shallower than the shallow alarm's setting or deeper than the deep alarm's set- ting. For example, if you set the shallow alarm to 10 feet, the alarm will sound a ton...

[Page 62] Eagle FISHMARK 640C

56 3. Press ← to Shallow Alarm ENABLED|ENT|EXIT. 4. To turn the alarm off press ALARM|ENT|EXIT. To switch to a different depth setting, open the Sonar Alarms menu and repeat the instructions in step 3 above. To adjust and turn on the Deep Alarm:...

[Page 63] Eagle FISHMARK 640C

57 Sonar Alarms menu (left) with Adjust Zone command selected. Adjust Zone Alarm selection box (right) with Upper Limit selected. 4. Press EXIT|← to Zone Alarm ENABLED|ENT|EXIT. Now, any echo — fish, bottom, structure — within the zone...

[Page 64] Eagle FISHMARK 640C

58 Sonar Alarms menu with Fish Alarm selected. The check box to the left is blank, indicating the alarm is turned off. To turn the Fish Alarm on: 1. Press ALARM|↓ to Fish Alarm|ENT|EXIT. 2. To turn off the alarm, press ALARM|↓ to Fish Alarm|ENT|...

[Page 65] Eagle FISHMARK 640C

59 The unit's backlight level can be controlled from the Screen menu. Calibrate Speed The speed sensor can be calibrated to compensate for inaccuracies. Be- fore you change the setting, first calculate the percentage that the speed is o...

[Page 66] Eagle FISHMARK 640C

60 Chart Speed The rate that echoes scroll across the screen is called the chart speed. The default is maximum. We recommend you leave the speed set at de- fault for virtually all fishing conditions. However, you might consider experimenting with ch...

[Page 67] Eagle FISHMARK 640C

61 1. From the Sonar Page, press MENU|↓ to CHART SPEED|ENT. 2. The Chart Speed Control Bar appears. Press ↓ to decrease chart speed or press ↑ to increase chart speed. 3. When it's set at the desired level, press EXIT. ColorLine Color...

[Page 68] Eagle FISHMARK 640C

62 Sonar Page menu (left) with ColorLine command selected. The ColorLine control bar is shown at right. Little ColorLine (left) indicates a soft bottom, probably sand or mud. The wider ColorLine (right) indicates a harder, rocky bot...

[Page 69] Eagle FISHMARK 640C

63 Sonar Page menu (left) with Depth Cursor command selected. Sonar chart (right) with the depth cursor active. The school of fish is 31.91 feet deep. The cursor can be moved to any location on the screen, letting you pin- point the depth of ...

[Page 70] Eagle FISHMARK 640C

64 Sonar Page menu (left) with Depth Range command selected. The Depth Range control scale is shown at right. 2. The Depth Range control scale appears. Press ↑ or ↓ to select a dif- ferent depth range. A blue bar highlights the selected ra...

[Page 71] Eagle FISHMARK 640C

65 NOTE: The sonar's depth capability depends on the transducer installa- tion, water and bottom conditions and other factors. FasTrack This feature automatically converts all echoes to short horizontal lines on the display's far right s...

[Page 72] Eagle FISHMARK 640C

66 There are several fish symbol sizes. These are used to designate the relative size between targets. In other words, Fish I.D. displays a small fish symbol when it thinks a target is a small fish, a medium fish sym- bol on a larger target and so on...

[Page 73] Eagle FISHMARK 640C

67 To turn the Fish I.D. feature on: 1. From the Sonar Page, press MENU|↓ to SONAR FEATURES|ENT. 2. Press → to FISH SYMBOLS|ENT|EXIT|EXIT. To turn off Fish I.D., repeat the instructions in step 2. FishTrack The FishTrack feature shows the de...

[Page 74] Eagle FISHMARK 640C

68 Frequency (Change Transducer Frequency) (SeaFinder unit only) The SeaFinder transducer operates with both 200 kHz and 50 kHz. The 200 kHz frequency has a 12° cone angle and the 50 kHz frequency has a 35° cone angle. The default frequency is 200 ...

[Page 75] Eagle FISHMARK 640C

69 To change the frequency setting to 50 kHz: 1. From the Sonar Page, press MENU|↓ to SONAR FEATURES|ENT. 2. Press ↓ then → to Transducer Freq.| 50 KHZ|ENT. 3. Press EXIT|EXIT to clear the menu. To change the frequency setting to 200 kHz: 1. ...

[Page 76] Eagle FISHMARK 640C

70 Overlay Data command (left) on the Sonar Menu. Overlay Data Shown selection menu at right. In this example, Depth will be displayed in a large font. When selected, the data type shifts to the top of the data list and a check mark appears be...

[Page 77] Eagle FISHMARK 640C

71 3. To return to the previous page, press EXIT. To turn off displayed data: 1. Press MENU|↓ to OVERLAY DATA|ENT. 2. Press ↓ or ↑ to select Data Type| ENT. The selected data type disap- pears from the top of the list and reverts to its previo...

[Page 78] Eagle FISHMARK 640C

72 Sonar Page with Overlay Data turned on. This example shows Depth, Water Temperature and Water Speed. NOTE: Some data types can be displayed in only one font size. If that is the case, the Data Size box will not be displayed for that data type. Pin...

[Page 79] Eagle FISHMARK 640C

73 When using HyperScroll, you may also need to manually decrease the sensitivity for optimum performance. Depending on water depth and other conditions, HyperScroll may cause a second bottom echo to return to the transducer during the next ping cycl...

[Page 80] Eagle FISHMARK 640C

74 2. The Sensitivity Control Bar appears. Press ↓ to decrease sensitivity; press ↑ to increase sensitivity. When it's set at the desired level, press EXIT. When you reach the maximum or minimum limit a tone sounds. To turn off HyperScroll: ...

[Page 81] Eagle FISHMARK 640C

75 Example showing the Pop-up Help message for the Sensitivity com- mand located on the Sonar Menu. Reset Options This command is used to reset all features, options and settings to their original factory defaults. This is useful when you have change...

[Page 82] Eagle FISHMARK 640C

76 Main Menu (left) with Reset Options command selected. The Reset Op- tions dialog box (right) with "Yes" selected. Reset Water Distance The sonar chart's Digital Data display option includes a box that shows distance travele...

[Page 83] Eagle FISHMARK 640C

77 grounding or striking underwater structure. The Keel Offset feature eliminates the need for the navigator to mentally calculate how much water is under the keel. Keel Offset lets you calibrate the digital depth, chart depth scale, chart cursor dep...

[Page 84] Eagle FISHMARK 640C

78 4. Press → to the second number, them press ↑ to change the num- ber to 5, then press EXIT. The depth indicators now accurately show the water depth from surface to bottom. Sensitivity & Auto Sensitivity The sensitivity controls the abili...

[Page 85] Eagle FISHMARK 640C

79 level in manual mode the unit will continue to use that exact sensitivity setting until you change it or revert to auto mode. To adjust sensitivity in auto mode: 1. Press MENU|ENT. 2. The Sensitivity Control Bar appears. Press ↓ to decrease sen...

[Page 86] Eagle FISHMARK 640C

80 NOTE: To return to the original factory setting for Auto Sensitivity, see the entry in this section on Reset Options. If sensitivity is in manual mode, the Reset Options command will switch back to Auto mode. Tip: For quicker sensitivity adjustmen...

[Page 87] Eagle FISHMARK 640C

81 To change the chart mode color scheme: 1. From the Sonar Page, press MENU|↓ to SONAR FEATURES|ENT. 2. Press → to SONAR CHART MODE|ENT. 3. Press ↓ or ↑ to Mode Name| ENT. 4. Press EXIT|EXIT to return to the Sonar Page. Sonar Page & S...

[Page 88] Eagle FISHMARK 640C

82 The FasTrack™ display shows just to the right of the scale. This changes all echoes into short horizontal bars, replicating a flasher so- nar. The zoom bar on the far right shows the area that's zoomed when the zoom is in use. (See the Zoom...

[Page 89] Eagle FISHMARK 640C

83 Split Zoom Sonar Chart. The left image shows the left split screen window zoomed to 2X. The right image shows the left split screen win- dow zoomed to 4X. Digital Data/Chart This mode shows the chart on the right side of the screen. The l...

[Page 90] Eagle FISHMARK 640C

84 Digital Data/Chart Customizing the Digital Data/Chart Screen The Digital Data/Chart screen can be customized to show digital data different from the defaults first shown. To customize this screen: 1. From the Sonar Page (in Digital Data mode), pre...

[Page 91] Eagle FISHMARK 640C

85 2. The Water Speed box title bar flashes, indicating the box contents can be changed. Press ENT|↑ or ↓ to select data type|ENT|EXIT. Water Speed has been selected to replace Water Depth in the top digital data box. Tip: You can customize othe...

[Page 92] Eagle FISHMARK 640C

86 Main Menu with Sonar Simulator command selected. The Simulator is turned off when the box is unchecked. NOTE: If you turn the unit on before attaching a transducer, it may enter a demo mode. The words "demo mode" flash on the bottom of ...

[Page 93] Eagle FISHMARK 640C

87 Sonar Menu with Stop Chart command selected. The box is unchecked, indicating that the chart is scrolling across the screen. Surface Clarity The markings extending downward from the zero line on the chart are called "surface clutter." Th...

[Page 94] Eagle FISHMARK 640C

88 Sonar Features menu with Surface Clarity selected (at left, dual- frequency menu; at right, single-frequency menu). 2. Press ↓ to select Surface Clarity|ENT. In the illustration at left, Surface Clarity is turned off. The right view ...

[Page 95] Eagle FISHMARK 640C

89 Experiment with this feature until you find the right level of transpar- ency for your eyes. Main Menu with Transparency command selected. To adjust Menu Transparency level: Press MENU|MENU|↓ to TRANSPARENCY|ENT. The TRANSPARENCY slider bar app...

[Page 96] Eagle FISHMARK 640C

90 The Units of Measure Menu. To set Units of Measure: Press ↓ to the desired units, then press ENT. After all the options are set as desired, press EXIT|EXIT to return to the page display. Volume This command adjusts the speaker volume, which cont...

[Page 97] Eagle FISHMARK 640C

91 Pressing ZIN once doubles the size (2X) of all echoes on the screen. Pressing it again quadruples the size of the echoes (4X). Press the Zoom Out key, ZOUT, to return the display to the normal mode. Sonar Page (left) in normal view. Same vie...

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92 Notes ...

[Page 99] Eagle FISHMARK 640C

93 Section 5: Troubleshooting If your unit is not working, or if you need technical help, please use the following troubleshooting section before contacting the factory customer service department. It may save you the trouble of returning your unit f...

[Page 100] Eagle FISHMARK 640C

94 Weak bottom echo, digital readings erratic, or no fish signals: 1. Make sure the transducer is pointing straight down. Clean the face of the transducer. Oil, dirt and fuel can cause a film to form on the transducer, reducing its effectiveness. If ...