[ICOM] IC761 Power supply

[Bert Almemo]

Hi Alan,

I read the message below on the reflector earlier today and maybe it can be
of some help. Good luck!

73 Bert, VE3OBU




 Jim,

As others mentioned check the power supply. But there is more.
If you take off the top cover you will find the internal power supply is
connected through a 6 pin DC connector most Icoms use. You can unplug the
internal supply and use an external supply to make sure the 765 works
normally from a 13.8 VDC 20 amp supply. PLEASE observe the correct polarity
and make sure the external DC cable is fused with 20 amp fuses. There are no
internal fuses in the 765 for the PA unit. 

If the 765 operates at full power the information below is a most common
trouble with the internal supply.

Inside of the power supply there is a flat bar about 1.5 inches long and 1/4
inch wide. Most likely the solder joints are cracked on one or both ends of
this bar. The bar is the power supply current shunt so all the current the
power supply generates goes through this bar. Its for the current limiting
capability of the supply. High current heats the now resistive joints and
they open thus causing current starvation.

The fix is not hard. You will need to remove the circuit board from the
power supply case. Get the Skill electric screwdriver warmed up as it will
see a lot of use. On the bottom of the circuit board you will see the flat
bar. Look closely for cracked solder. I suggest you remove the bar, clean up
the solder with some solder wick or other de-soldering equipment. Replace
the bar, I like to use liquid solder flux when doing this and re-solder it
into place. DO NOT solder the length of the bar or go past the two holes
drilled into the bar. Doing so will change the resistance of the bar and the
current limiting of the power supply. reassemble and reinstall the power
supply and give it a try.

I hope this helps.

Gary K8IZ
 -------------- Original message ----------------------
From: "James Bartlett" <jimbartlett at oceanfree.net>
> Hi Guys,
> I am looking for help. A friends '765 has gone faulty.
> It receives ok. The problem is on transmit.
> When keyed in the SSB mode it is ok until talking into the mic, then 
> it shuts down completly. In AM or RTTY mode it shuts down straight away.
> I am wondering if this is a PA or Power Supply problem and am looking 
> for any advice before starting to pull tyhings apart.
> Any help greatly appreciated.
> Thanks in advance
> 
> Jim. Ei2BB
> ----
> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net Icom 
> Users Net: Sundays, 1700Z, 14.316 MHz Icom FAQ: 
> http://www.qsl.net/icom/


----
Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net Icom Users
Net: Sundays, 1700Z, 14.316 MHz Icom FAQ: http://www.qsl.net/icom/

-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of zl3kr
Sent: Monday, April 24, 2006 10:43 PM
To: Icom
Subject: [ICOM] IC761 Power supply

While operating PSK (approx 20-25 watts out) the overload cut in and closed
the rig down. After 2 to 3 minutes I switched back on and it powered up ok,
however as soon as I went to transmit it shut down again.
I repeated this a couple of times with same result but then tried the rig on
CW and SSB where it was able to run full power, went back to PSK and it shut
down again.
Now on trying to switch on again the overload relay clicks in about 3 times
and shuts down straight away.
A visual inspection of the Power Supply shows no signs of Capacitor leakage
or overheating on the PC Board.
I wonder if anyone has any suggestions as to the most likely place to start
looking for the problem please. I appreciate any help.
Alan ZL3KR

----
Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net Icom Users
Net: Sundays, 1700Z, 14.316 MHz Icom FAQ: http://www.qsl.net/icom/