Hitachi P50A202/D8UF, Service Manual

Page: 6 / 92

D8UF
TABLE OF CONTENTS
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 600°F to 800°F.
2. Use an appropriate lead free solder (see page 8). Lead
solder can be used, but there is a possibility of failure due
to insuf
fi cient strength of the solder.
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
(600°F to 800°F).
b. Heat the component lead until the solder melts.
Quickly draw away the melted solder with an antistatic,
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
(600°F to 800°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
fl ows 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 the leads.
IC Removal/Replacement
Some Hitachi unitized chassis circuit boards have slotted
holes (oblong) through which the IC leads are inserted
and then bent
fl at 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.
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 the three leads
remaining on the circuit board.
3. Bend into a “U” shape the replacement transistor leads.
4. Connect the 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 the 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.