[ICOM] 761 Problem

[Vladimir Sidorov]

As a temporary solution the following may cure the problem for some time.
- First, locate the 4 trimmers. Make sure, you note particular positions of 
their rotors.
- Rotate each of the rotors back and forth several times +/-45-90 deg around 
the noted original position.
Leave the rotors back in the original position.

By doing so you mechanically destroy chemicals (resins or oxides, whatever) 
accumulated between rotors and stators.

You may do so even keeping the radio on. Sometimes it is just 1 trimmer 
failing. When you massage the falty one, after a few moves the oxide may go 
and you immidiately hear a totally dirrefent sound in the speaker, i.e. the 
receiver is back to its normal state. Obviously it would be good to check 
the loop voltage afterwards and adjust it, if necessary.

Although temporary, this little massage may leave your radio working for 2-3 
years. Then you can repeat the procedure actually.

Replacing trimmers to ceramic ones helps once and forever, but it requires a 
lot of massive soldering on the fragile board.

73,
Vladimir VE3IAE

---


----- Original Message ----- 
From: "Wayne Johnson" <vk6eh at westnet.com.au>
To: "ICOM Reflector" <icom at mailman.qth.net>
Sent: Thursday, August 12, 2010 1:26 AM
Subject: [ICOM] 761 Problem


> Gday Allan, Sounds like the PLL VCO's are either unlocked or on the
> verge of unlocking. Most of that generation of Icoms had bad plastic
> trimmer caps used to set up the lock voltage in the individual vco's,
> over time they become faulty (some say because of resin contamination
> from when they were first soldered into place.You may find some bands
> are OK, there's 4 of them in the radio and it's a common failing
> Replace them with good quality ceramic types, they were available at
> Altronics (Check the service manual for values required)
> Easy the replace and setup the correct loop voltage, the service manual
> shows the procedure for adjustment, you should only need a good digital
> Multi meter.
> Best to check the loop voltage first for the band and frequency as
> detailed in SM, if it is not at spec. replace the trimmers.
>
> Cheers and all the best
>
> Wayne
> VK6EH
> ----
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