Service manual

CM153 - 923-923-03443R1 5 ZLD20A1 - SERVICING
SERVICING
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 or 500cF to 600cF.
2. Use an appropriate gauge of RMA 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
mall wire bristle (0.5 inch, or 1.25cm) brush with a
metal handle. Do not use freon-propelled spray-on
cleaners.
5. Use the following unsoldering technique
a. Allow the soldering iron tip to reach normal
temperature. (500cF to 600cF)
b. Heat the component lead until the solder
melts.
c. Quickly draw 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 a normal
temperature (500cF to 600cF)
b. First, hold the soldering iron tip and solder
the 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.
d. Closely inspect the solder area and remove any
excess or splashed solder with a small wire-
bristle brush.
IC REMOVE/REPLACEMENT
Some 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.
REMOVAL
1. Desolder and straighten each IC lead in one opera-
tion by gently prying up on the lead with the solder-
ing iron tip as the solder melts.
2. Draw away the melted solder with an anti-static suc-
tion-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 the
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 the replacement transistor leads to the cor-
responding 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 DEVICE
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 heat sink of
the circuit board.
4. Insert new transistor in the 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 perpendicular 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.
FUSE AND CONVENTIONAL RESISTOR
REMOVAL/REPLACEMENT
1. Clip each fuse or resistor lead at top of the circuit
board hollow stake.
2. Securely crimp the leads of replacement component
around notch at stake top.