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ICOM IC-745
EXPD. RF
1- Remove the power and antenna.
2- Remove the screws and open the radio.
3- Locate RF board on the side of the radio.
4- CUT the light brown wire on J7 pin 1.
5- Reassemble the radio.
IC745
IC-745 - PROBLEM: TUNING COUNTS SLOWLY DOWN
I have a problem with my 745. When I rang Bellevue, WA, they said: Never
heard of it. My friend in LA who has the
same problem got the same answer. The problem is as follows:
The tuning counts slowly DOWN whether it's memory or VFO. I temporarily
used the set by turning the dial in the UP
direction faster than the countdown and then used the lock button when the
set arrived on the desired frequency. The
XIT?RIT can be used for small corrections. My friend who has a complete
professional lab at his disposal found a
temporary fix. He grounded pin 40 of the I/O IC which steers the CPU.
Everything works fine except that you miss the slowest tuning speed and
that the UP/DOWN button on the mic does not work. I did the same and my
set work the same. The tuning is a little bit coarse now but usable except
you have to be careful especially with RTTY or AMTOR. The local ICOM
repair shop is too busy at the moment with their normal wo4k, and I don't
like to be without this set for too ong a time.
I can't use the 730 to drive my linear at least not without a lot of
trouble. I suspect that one of the two transistors
has gone but which? I just wonder if any of your readers has had the same
problem and fixed it. (ED Note: Anyone have the solution?) (Thanks, Bob
Bartelings, VE6CBN, 170 Haysboro
Crescent, Calgary, Alberta Canada T2V 3G3)
RELAYED BY...N0KGX...GENE
| Icom IC-745 (IC 745 IC745) RAM Card Backup
Battery Replacement Instructions |
| In the early 1980s Icom America
marketed a group of transceivers and radios that utilized the
latest state-of-the-art computer technology to enhance the
operation of the radios. This technology improvement allowed
hams to afford a reasonably priced high performance transceiver
which until then was only available on units costing much more.
Features now available to the hams included: higher frequency
stability, better frequency resolution, digital frequency
display, almost instant recall of saved frequencies (memory
channels), quick mode signal processing and built in tones and
offsets for the rapidly emerging repeater operation.
Implementation of all these features
required a CPU with associated logic circuitry. In the early
80s, the most cost effective way to implement data processing
and memory functions was through a DRAM (Dynamic Random Access
Memory) to control the CPU. This DRAM was a volatile memory
integrated circuit which required a lithium battery to retain
its instruction set. The following receivers and transceivers
had such RAM units:
IC-271 ; IC-471 ; IC-1271 ;
IC-745 ; IC-751/A ; IC-R71A
The lithium batteries in these units
typically lasted about 5 to 7 years before replacement was
required. This was specifically noted in each of the Owners
Manuals for the products.
This lithium battery can be replaced by
the radio owner if care is used. The following is a recommended
procedure to accomplish this:
Procedure
- Disconnect the power cable from
the radio, and take the cover off.
Unplug the RAM board and remove it from the radio.
Temporarily solder a 3 Volt DC battery source across the
existing battery terminals (see suggested connection points
on the circuit board pictures).
Unsolder the old lithium battery and replace it with a new
one. (BR2325 1HC, ICOM stock number 945 03112)
Unsolder your temporary 3 Volt DC source.
Reinstall the RAM board into the radio.
Cautions
- Do not use an AC powered 3 Volt DC
source, your grounded soldering iron tip could short out the
battery (+) terminal. Use a 3 Volt battery DC source only (2
alkaline cells for example).
Do not solder the external DC wires directly to the lithium
battery tab pads. If you do so, you will not be able
unsolder the battery without having the wires drop off.
If by accident you lose power to the RAM unit it must be
sent to Icom America for reprogramming.
Be careful not to damage or bend the connector pins on the
radio side while removing or reinstalling the RAM card.
Pictures
There are two versions of the ICOM RAM
boards. Both are identical in operation, and they are
interchangeable. The differences are in the circuit board
layouts only. Note that the black and red wires visible on these
images are the suggested way of connecting the external DC
backup voltage while the battery is being replaced. The wires
are not a part of the RAM card, and should be removed when the
battery replacement procedure is complete. Refer to the
replacement procedure outlined above.
RAM card version A images:
 
RAM card version B images:
 
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| Icom IC-745 Cure for drift problem |
Hello all, I read recently an article about
changing out the notorious
C5 variable trimmer on the 2nd IF board.
What I did was to change the 30 pf variable to a 2-5pf variable and
change the 6pf fixed under the board to a 27 pf NPO type. Before this
change I would have a drift of about a 25-30 hz over a several hour
period. Now after changing these two components out it is down to about
a 2-3 hz drift! The rig is rock stable now. Hope this helps those who
have this fine rig!
By W4SEF |
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KB2LJJ