Hitachi 51SWX20B Service Manual Download

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DP27/27D

General Soldering Guidelines

1. Use a grounded-tip, low-wattage soldering iron and

appropriate tip size and shape that will maintain tip
temperature within the range 500°F to 600°F.

2. Use an appropriate gauge of resin-core solder composed

of 60 parts tin/40 parts lead.

3. Keep the soldering iron tip clean and well-tinned.

4. Thoroughly clean the surfaces to be soldered. Use a

small wire-bristle (0.5 inch or 1.25 cm) brush with a metal
handle. Do not use freon-propelled spray-on cleaners.

5. Use the following desoldering technique.

a. Allow the soldering iron tip to reach normal

temperature (500°F to 600°F).

b. Heat the component lead until the solder melts.

Quickly draw away the melted solder with an anti-
static, suction-type solder removal device or with
solder braid.

CAUTION:

Work quickly to avoid overheating the
circuit board printed foil.

6. Use the following soldering technique.

a. Allow the soldering iron tip to reach normal

temperature (500°F to 600°F).

b. First, hold the soldering iron tip and solder strand

against the component lead until the solder melts.

c. Quickly move the soldering iron tip to the junction of

the component lead and the printed circuit foil, and
hold it there only until the solder flows onto and
around both the component lead and the foil.

CAUTION:

Work quickly to avoid overheating the
circuit board printed foil or components.

d. Closely inspect the solder area and remove any

excess or splashed solder with a small wire-bristle
brush.

Removal
1. Desolder and straighten each IC lead in one operation by

gently prying up on the lead with the soldering iron tip as
the solder melts.

2. Draw away the melted solder with an anti-static suction-

type solder removal device (or with solder braid) before
removing the IC.

Replacement

1. Carefully insert the replacement IC in the circuit board.

2. Carefully bend each IC lead against the circuit foil pad

and solder it.

3. Clean the soldered areas with a small wire-bristle brush.

(It is not necessary to reapply acrylic coating to areas.)

“Small-signal” Discrete Transistor Removal/Replacement

1. Remove the defective transistor by clipping its leads as

close as possible to the component body.

2. Bend into a “U” shape the end of each of three leads

remaining on the circuit board.

3. Bend into a “U” shape the replacement transistor leads.

4. Connect to replacement transistor leads to the

corresponding leads extending from the circuit board and
crimp the “U” with long nose pliers to insure metal to
metal contact, then solder each connection.

Power Output Transistor Devices Removal/Replacements

1. Heat and remove all solder from around the transistor

leads.

2. Remove the heatsink mounting screw (if so equipped).

3. Carefully remove the transistor from the circuit board.

4. Insert new transistor in circuit board.

5. Solder each transistor lead, and clip off excess lead.

6. Replace heatsink.

Diode Removal/Replacement

1. Remove defective diode by clipping its leads as close as

possible to diode body.

2. Bend the two remaining leads perpendicularly to the

circuit board.

3. Observing diode polarity, wrap each lead of the new

diode around the corresponding lead on the circuit board.

4. Securely crimp each connection and solder it.

5. Inspect (on the circuit board copper side) the solder joints

of the two “original leads”. If they are not shiny, reheat
them and, if necessary, apply additional solder.

Use Solding Iron to Pry Leads

IC Removal/Replacement

Some Hitachi unitized chassis circuit boards have slotted
holes (oblong) through which the IC leads are inserted and
then bent flat against the circuit foil. When holes are the
slotted type, the following technique should be used to
remove and replace the IC. When working with boards using
the familiar round hole, use the standard technique as
outlined in paragraphs 5 and 6 above.

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