FAQ: The Sony ICF-SW100 Ribbon Cable Failure Problem
Michael Rathbun
rec.radio.shortwave regarding the ribbon cable failure on the Sony ICF-SW100:
why it happens, how to identify it, how to prevent it, and how to repair it
yourself.
Last updated: 24 Nov 99: Signal cable may also develop breaks, Sony has
modified design to correct this problem.
NOTE: This problem was addressed by Sony in a major revision of both the
SW-100 and SW-77 in the Fall of 1997. (Thanks to Lee Rothman for this
information.) I have not received reports of failures of units incorporating
the design change.
Some of the information was originally presented by jpd <at>
space.mit.edu (John Doty). The remainder comes from m...@HONet.com
(Michael Rathbun).
THE PROBLEM:
The upper and lower modules of the SW100 are interconnected by two
ribbon cables, or "Flexible PC Boards" as they are called in the Sony
service manual parts list. The microprocessor that controls the
operation of the receiver is in the lid assembly, and its interface to
the keyboard and receiver electronics in the base (or "chassis")
assembly passes through these cables.
The edge of the plastic at the point on the lid module where the ribbon
cables exit is very sharp. In a test, it functioned as an efficient wire
cutter for 30-gauge bare copper wire. When the lid is closed, the inner
("Key") ribbon cable is pulled taut and makes a bend of over 90 degrees
with a bending radius of, essentially, zero.
Copper does not forgive this sort of insult. Over time, the key ribbon
cable will develop breaks in the copper conductors, which will cause
various keys on the keyboard to stop working, including the on/off
switch. The Signal ribbon cable may also develop problems -- I
have observed this in one case so far.
CHECKING THE RIBBON CABLES:
You can check the condition of the ribbon cables by disassembling some
parts of the receiver as described below, and inspecting the conductors.
If you have the correct screwdriver, you may separate the lid portion
from the base (chassis) portion to look at the cable; if not, you may
disassemble the upper and lower halves of the receiver and remove the
cables from the receiver for inspection.
The break in the conductor may be very difficult to see -- nothing more
than a slight discoloration of the copper at the point of the break.
PREVENTING (OR AT LEAST DELAYING THE ONSET OF) THE PROBLEM:
Separating the lid and base assemblies of the receiver gives you the
opportunity to use a small file to dull the extremely sharp edge that
causes the fatal bend in the conductor.
The steps:
1. Disassemble the LID assembly
2. Disconnect the ribbon cables
3. Separate the LID and CHASSIS assemblies and carefully pull the
cables out of the trough in the lid
4. Use a file to dull the plastic edges where the cables exit the lid
5. Reverse steps 1-3 to reassemble the receiver.
The lid assembly is fastened to the base assembly by two long screws
requiring a small (about 0,7 mm) cross-point screwdriver. They are made
of soft metal and it is very easy to damage these screws with incorrect
tools or careless operation.
The upper lid portion disassembles easily, as the two halves snap
together. The ribbon cables slip into two sockets on the circuit card.
The sockets have locking strips that should be released before removing
or inserting the ribbon cable.
REPAIRING THE RECEIVER:
Sony part numbers for the replacements are:
1-651-256-11 PC BOARD, FLEXIBLE (KEY)
1-651-257-11 PC BOARD, FLEXIBLE (SIGNAL)
Beware that in the service manual, these part numbers are interchanged.
"Supplement 2" to the manual corrects this error.
In the USA, Sony parts can be ordered by calling (800) 488-7669.
These are about $11 apiece. (This information current as of October,
1997.)
It is possible that both cables may have developed defects; the "Key" cable is
the most likely to have been damaged, as it is in contact with the sharp
plastic edge.
The steps:
1. Disassemble the lid and chassis units (no need to remove hinge
screws)
2. Remove cables
3. Replace cable(s)
4. Reassemble
The cover of the lid is held on only by plastic claws, so it is easy to
remove. The lower (chassis) portion has four screws in addition to
claws: remove the screws identified by arrows on the bottom piece. The
fifth screw you'll see (with no arrow) anchors the whip antenna: it need
not be removed. Once you've removed the screws and unhooked the claws,
the chassis separates into three pieces: the upper part consisting of
the lid, the top of the battery case, and the keyboard cover; the middle
part holding the two circuit boards; and the lower cover.
The flexible boards plug into connectors on the circuit boards, so no
soldering is necessary. The connectors into which the ends of the
flexible circuit board slide are fitted with a bit of white plastic
which is a lock/release mechanism. Before pulling out the damaged flex
board, pull out the lock/release piece on the connector.
The boards are routed through a slot by the lid hinge. They only move
freely when the lid is open: with the lid closed they are tightly
pinched (this is the origin of the problem).
Be sure to fold the replacement the same way the original was folded.
The silvered fingers on the end go toward the board when you plug it
into the connector. When inserting the replacement part, be
certain that the lock/reliece piece is pulled out; the flex board will
then slide into the connector quite easily. When it is seated, push the
lock/release piece into the connector.
As is usual with Sony products, reassembly is a bit like trying to
line up a dozen live worms. Getting the plastic keys and the Main
Power toggle to stay in place while you snap the chassis together
is tricky, especially with the lid open to keep the flexible boards
from jamming. Once the chassis is snapped together, the rest is
easy.