[Icom] Replacing the IC756 display

[D & P Graham]

Hello All,





Having recently replaced 
the LCD display in my ICOM 756 I 
thought that others may like to share the experience. It 
probably isn't for everyone but some may be in a position where 
there isn't any alternative but to tackle the repair 
themselves.





73...Don VK6HK

                                   ----------------
---------





                   REPLACING 
THE LCD DISPLAY IN THE ICOM IC-756

                     ------------------------------------------       




A common fault with the 
first model of the ICOM IC756 series 
(not to be confused with the PRO and PROII) is the partial 
failure of the main LCD display by the appearance of a number 
of prominent horizontal lines (dark in my case). The lines are 
usually intermittent but persist. The only cure is to replace 
the LCD display, which in my case was supplied by the 
Australian Agent for ICOM. They would have undertaken the 
repair as well (for a price) but that would also have

entailed freighting the 
transceiver some 3500Km with attendant 
costand further risk of damage in transit.





This is an account of 
the process necessary to replace the 
display, where alternative repair facilities are not available.





If anyone follows this 
procedure the responsibility for any 
damage is of course theirs.





The ICOM part number 
for the LCD display is:





Ref No: DS1 Order No: 
5030001420 Description:  DG041Z-5DC




Before starting provide 
a container for all the loose screws, 
knobs etc that will be removed and must later be replaced!





Take anti-static precautions.





PROCEDURE:





(1) Remove the top and 
bottom covers and the carrying handle.





(2) Remove the rubber 
grip (it slides off) on the Main Tuning 
knob exposing  a hole in the knob leading to an Allen key grub 
screw. Loosen the screw and take off the knob.





(3) It is not necessary 
to remove the braking mechanism 
revealed under the main knob. The associated two screws (one 
plated self tapper and one black adjusting screw just above the 
{quot}lock{quot} button) do not prevent removal of the panel.




(4) Remove all other 
panel knobs. They just pull off with a 
firm grip. No other controls, including the microphone 
connector prevent panel removal.





(5) Now remove the front 
plastic panel. This is held in place 
by six lugs on the top and bottom edges. It is necessary to use 
say a thin bladed knife to gently ease the plastic over the 
lugs while putting forward pressure on the panel. The panel is 
a snug fit and care must be taken to avoid any damage. The 
panel will not come completely away as it mounts a PCB with 
three short ribbon cables which attach to the {quot}next layer{quot} - a 
metal subchassis. Take care not to stress these cables at this 
stage.





(6) Remove the metal 
subchassis behind the front panel (to 
which it is still attached by the three ribbon cables) from the 
main diecast chassis by removing the four screws (two on each 
side). Carefully draw the subchassis forward, limited by 
attached cables.





(7)  At this stage 
it is possible to see that the only way to 
separate the component boards and panels is to remove a number 
of miniature ribbon cables, audio and power plugs. The 
miniature ribbon {quot}header{quot} type plugs need care but easily 
unplug. They use contacts moulded  or plated on to the end of 
the ribbon cable and appear fragile. Carefully note where each 
plug comes from, although it is fairly difficult to

make an error on reassembly 
(except to forget to reconnect 
something). Separate the plastic panel from the metal sub 
chassis by disconnecting its three cables.





(8) To remove the LCD 
itself it is necessary to remove the sub-logic board which is mounted on the metal sub chassis. Remove 
the securing self tapping mounting screws from the board and 
all cable connectors.It is  necessary to undo the mounting nuts 
on the AF/RF pot and the BAL/NR pot. It is also necessary to 
unsolder the two connections to the S meter (marked with two 
white arrows on the board) and withdraw the S-meter forwards. 
Note that the meter movement is unprotected once the plastic 
front panel is removed and avoid damaging the meter pointer and 
movement while working on the panels. Stow the meter in a

safe place.





(9) Note that one ribbon 
cable connects the LCD to the main 
chassis and this cannot be unplugged until the sub logic board 
is removed, so take care not to strain or damage this cable in 
the process. It could be a good idea to locate the other end of 
this ribbon on the main chassis and unplug it there so giving 
more freedom of movement.





(10) Carefully remove 
the sub-logic board. Now the LCD itself 
is exposed and can be removed. It is held by two screws and two 
detents. There is one power plug and one ribbon cable. The 
ribbon cable is further restrained lightly by a strip of self 
adhesive reinforced packing tape. This latter cable is the one 
that connects to the main chassis as in (9). Remove the cables 
and the adhesive strip and the LCD and its attached board.





(11)  The LCD is 
fitted with a separate black anodized 
escutcheon which is a separate ICOM part number:





Ref No: MP43  Order 
No: 8930042810  Description: 1876 LCD 
cover.





When ordering the LCD, 
it is recommended that a new escutcheon 
also be ordered to go with the new display. I did not realize 
this and was obliged to try and salvage the old escutcheon. 
This was possible - just, as the escutcheon was originally 
attached to the old LCD with some sort of strong adhesive. A 
knife with a thin long blade was used in this case to prize off 
the escutcheon. It is easily possible to damage the part

beyond repair so be careful 
if you must re-use the old one.





(12) Proceed to re-assemble 
in the reverse order, starting with 
the LCD, taking particular care to correctly re-seat the ribbon 
cables, and not forgetting to re-solder the S-meter in place. 
The escutcheon can be refitted once the LCD is screwed into 
place. Don't forget to replace the adhesive tape re-inforcing 
the cable from the main chassis to the LCD board, or the nuts 
from the AF/RF and NR/BAL controls.





The plastic front panel 
just clicks into place over its six 
lugs.





(13) On switching on, 
no problems were encountered that 
required re-setting of the CPU. All memory data was unaffected. 
However the time display did show 00.00 and counting, so had to 
be reset to the correct time from the menu. (See users manual). 
The lithium battery for the clock is mounted on the front panel 
and is obviously disconnected via one of the cables removed 
during the dismantling.









REMARKS:





(a) Some of the processes 
are awkward because of the limited 
length of the ribbon cables, but are achievable. There may be a 
better way to go about the repair but these notes are provided 
to assist those who have wondered if it is a feasible {quot}do-it-yourself{quot} exercise.




(b) At first inspection 
it seems that one can avoid the need to 
remove the plastic front panel thus saving a deal of effort. 
However the critical path in this exercise is the unavoidable 
need to undo the mounting nuts for the AF/RF gain and NR/BAL 
control so that the sublogic board can be removed to get at the 
LCD. This cannot be done with the front panel in place - 
unfortunately.





(c) A service manual 
was available and is always a useful aid. 
However it is not really essential as it contains little more 
than board layouts, circuit diagrams and parts lists. The most 
useful section for this exercise is perhaps the one containing 
{quot}exploded{quot} mechanical views. It does not tell one how to get 
everything apart however. 





.............VK6HK





                                   
-----



--- StripMime Report -- processed MIME parts ---
text/html (html body -- converted)
The reason this message is shown is because the post was in HTML
or had an attachment. Attachments are not allowed.
Please post in Plain-Text only.---