Hitachi 50V500 Service Manual page 5

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 sodering 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.
Use Soldering 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 follow-
ing 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.
Removal
1. Desolder and straighten each IC lead in one operation by gent-
ly 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 sol
der 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 remain-
ing 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/Replacement
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 pos-
silbe 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.
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LC37/LC37F