HITACHI DH 20DV User guide

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1. REPAIR GUIDE

Without fail, remove the EB 24B battery from the main body before starting maintenance work. Because the
tool is cordless, if the battery is left in and the switch is activated inadvertently, the motor will start rotation
unexpectedly, resulting in serious hazard.

1-1. Precautions and Suggestions for Disassembly and Reassembly of the Main Body

The [Bold] numbers in the descriptions below correspond to the item numbers in the Parts List and
exploded assembly diagrams.

1-1-1. Disassembly

(1) Disassembly of the chuck section

As shown in Fig. 1, slide the Grip [2] in the direction
indicated by the arrow mark, and remove the Front Cap
[1]. The Grip [2], the Ball Holder [3] inside the Grip,
Holder Spring [4] and two Steel Balls [9] can then be
removed from the Cylinder [11].

(2) Disassembly of the housing

After removing the chuck section, loosen and remove the nine D4 x20 Tapping Screws (Black) [33] and
the two D4 x14 Tapping Screws [32] which fix the main body. Then, separate the Housing (A)(B) Set
[31] by removing Housing (B) from Housing (A).

(3) Disassembly of the hammering mechanism section

When the Cylinder [11] and the Piston [21] are removed from Housing (A) in a single body, the arm of
the Reciprocating Bearing [40] will be extracted from the Piston [21]. Then extract the Piston [21] from
the Cylinder [11], and with a screwdriver or slender rod push the Second Hammer [16] out through the
hole in the tip end of the Cylinder [11] to disconnect the Striker [19] retained by O-Ring (D) [18].
Pull out the First Gear [44] without the bearing from the Second Pinion [36]. Then remove the Collar
[41] and the Reciprocating Bearing [40]. Next, move the Clutch [38] toward the pinion side at the top of
the Second Pinion [36], and remove the O-Ring [39]. The Clutch [38] and the Clutch Spring [37] can
then be removed from the Second Pinion [36]. Remove the Retaining Ring for D14 Shaft [50] which
fixes the Change Lever [46] on the inner side of Housing (A), and extract the Change Lever [46] from
Housing (A). Be very careful not to lose the D3.97 Steel Ball [48].

(4) Disassembly of the cylinder and the second gear (slip mechanism section)

Extract the Retaining Ring [5] from the Cylinder [11]. Pull the Oil Seal [6] off of the Cylinder [11].
Extract the Retaining Ring for D20 Shaft [7], and remove the 6904CM Ball Bearing [8] from the Cylinder
[11] with a bearing puller. Be very careful not to lose the four D5.556 Steel Balls [10]. The Second
Gear [12], Spring (A) [13] and Washer (A) [14] can then be removed from the Cylinder [11]. Extract O-
Ring (D) [18] from deep within the Cylinder [11], and remove the Second Hammer [16] from the Cylinder
[11]. [O-Ring (D) can be easily removed by using the J-201 spring hook (Code No. 970977 is
recommended) to pull it out from the outside.] To prevent idle hammering, be sure to replace O-Ring
(D) [18] whenever the unit is disassembled.

Fig. 1

Front Cap [1]

Grip [2]

Housing (A),(B) Set [31]

MODEL DH 20DV

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(5) Disassembly of the switch and the terminal

Remove Housing (B) and pull out the Internal Wires [54] [55] from Brush Holder (L) [59] and (R) [60].
Then the Terminals [66] [68], the Switch [53] and the Internal Wires [54] [55] can be removed together.
Perform the following procedure for disassembly of the Terminals [66] [68], the Switch [53] and the
Internal Wires [54] [55].
Disconnect the Internal Wires [54] (red) and [55] (black), and the Terminals [66] (brown) and [68] (blue)
from the Switch [53] by melting their soldered connections with a soldering iron (350 ˚C, within 5
seconds). Take care not to apply too much heat because it can damage the variable-speed function of
the switch. Remove the two D4 Tapping Screws [65] from the Terminals [66] [68].

(6) Removal of the rubber seal

Pull out Rubber Seal (A) [63] gently from the Oil Seal [6] on the housing ass'y. Pull out Rubber Seal (B)
[64] by sliding with your fingers. Take care not to scratch the rubber seals to prevent grease leakage.

(7) Removal of the armature and the magnet

Hook the spring of Brush Holder (L) [59] and Brush Holder (R) [60] on the edge of each Brush Holder.
Then remove the Armature [28] and the Magnet [29] together.

(8) Removal of the brash holders

Remove the two D3 Tapping Screws [58] from both sides of Brush Holder (L) [59] and also Brush Holder
(R) [60] (four in total). Then Brush Holders can be removed.

(9) Replacement of the carbon brushes

Remove the Armature [28] and the Magnet [29] together according to the step (7). Pull out each
terminal of the Carbon Brushes [57] from the brush holder terminal with a small flat-blade screwdriver,
and then remove the Carbon Brushes by pulling them inward. Push each terminal of the new Carbon
Brushes in the Brush Holder as far as it will go. Be careful not to contact the spring of the Brush Holder
with the wire of the Carbon Brush (pay attention to inserting orientation of the Carbon Brush) or not to
hook the spring on the edge of the Brush Holder. Thus, the two Carbon Brushes can be replaced.

1-1-2. Reassembly

Reassembly can be generally be carried out as the reverse of the disassembly procedures, with some items
to be noted as follows:

(1) Be sure to perform wiring connection as indicated in Fig. 2.
(2) Pay attention to the polarity of the Terminal Piece [67], and the Internal Wires [54] and [55] when

mounting them to Housing (A). Be careful that the blue and brown Internal Wires cross at the midpoint.

(3) Insert the Armature [28] into the Magnet [29] facing its no-notch side inward. Be careful not to scratch

the Armature [28] because the magnet attracts the Armature [28].

(4) Position the Washer [43] between the wall of Housing (A) and the V-ring [42] when mounting the

Second Pinion [36] to the main body. Be careful not to position the Washer [43] between the wall of
Housing (A) and the First Gear [44].