[Icom] re sick IC-745

Fri, 7 Feb 2003 08:30:44 -0800

Ok Frank, I really appreciate your help with this. When I last checked the
voltages out of the regulator board (small one on the left side) it showed
all ok but I recall that earlier there was only 2.5 volts dc to the 2nd
oscillator board rather than 7.5 vdc but somehow that's cleared itself so
maybe I should check that reg board again. When I came home last night (late
again) I pulled the logic board out to check for cracks on soldering but
couldn't see anything there. I will resolder them all just for good measure.
I see that whoever tried to fix this rig before has resoldered the pins on
iC-12 and also IC-2.  Now when I look at the back side of the pc board, I
see a diode connected from (band side to pin 1) pin 1 to pin 39 and another
one from pin 39 to pin 38 (with band side to pin 39).  I don't see those
diodes shown on the schematic at all! I really thing that these two diodes
were added. Also noticed the R21 which connects to J2 on the 28M line is
removed (I think this has to do with selection of high/low power 100/50
watts).
    Although I've been in the repair of commercial radios for years, logic
stuff is something that I have really never learned. This rig may be a good
point for me to start. Got a few pointer from Adam Farson but he did tell me
that you are the "guru" on fixing these Icoms so if you don't mind I will
keep reporting to you with my findings.  I do have a good oscilloscope so
will be very receptive at any of your suggestions as to what to do.
    73 and do have a good day. It about -12 Celcius this morning so it's
going to be cool in working outside today with some installs. Got to do a
Globalstar satellite phone/cellular phone installation a loggers truck (my
first one from scratch all new installation) so should be interesting.  The
prices on those has finally tumbled down to around $1K cdn but the "car kit"
which allows handfree operation plus use of external antennas is still too
high at around $1.5 K cdn. Air time usage costs have also come down to a
more affordable price.  The older technology was bulky and very pricy at
around $6K cdn not too long ago.
    Fern

-----Original Message-----
From: Frank A. Ellis <[email protected]>
To: [email protected] <[email protected]>
Cc: [email protected] <[email protected]>
Date: Wednesday, February 05, 2003 6:14 PM
Subject: Re: [Icom] re sick IC-745


>Fern,
>
>If you don't have a frequency display, the Logic Unit or RAM Unit is most
>likely where the problem is. Since you subbed in a known good EX-314
>already, look elsewhere. Even with the VCO caps bad and an unlocked PLL,
you
>will still see a frequency display. Check for bad solder joints or cracked
>traces around the Logic Unit PCB header pins where the EX-314 RAM Unit
plugs
>into the Logic Unit, and check the Vcc source on the Logic Unit board, also
>make sure the outputs from the Regulator Unit (on the radio left sidewall)
>are OK.
>
>All that being good, probe around the processor and look for heartbeats, it
>sounds like the uP is not running and executing opcode from RAM to
>initialize the radio. If you see a good uP clock, there should be activity
>on the processor when the main dial is changed, or when any other main
>function is exercised.
>
>It could be simple, or it could get real ugly . . .
>
>Good Luck.
>
>73, Frank W3UHF
>
>
>>From: "Fern Rivard" <[email protected]>
>>Reply-To: [email protected]
>>To: <[email protected]>
>>Subject: [Icom] re sick IC-745
>>Date: Wed, 5 Feb 2003 18:24:39 -0800
>>
>>     I just acquired another Icom IC-745 transceiver. I found that the
>>lithium battery in the ram board was dead. I substituted the good ram
board
>>from my good working 745 but radio was still dead (no receive or transmit
>>and no frequency display). I then hooked my spectrum analyser to the
output
>>of the VCO and no output there. It does not receive or transmit on any of
>>the bands so I would think that it's not likely that it's just the VCO
caps
>>that need replacing or do they all go bad at once??  Anyone with a lot of
>>experience on these that could give me some more insight as to what to
>>check
>>out next.  I will be ordering the Nardo memory board from IK2RND rather
>>than
>>use the unreliable original Icom ram board.
>>     73 from Fern
>>
>>
>>----
>>Your Moderator: Dick Flanagan W6OLD, [email protected]
>>Icom Users Net: Sundays, 1700Z, 14.315 MHz
>>Icom FAQ: http://www.qsl.net/icom/
>
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>----
>Your Moderator: Dick Flanagan W6OLD, [email protected]
>Icom Users Net: Sundays, 1700Z, 14.315 MHz
>Icom FAQ: http://www.qsl.net/icom/
>