[R-390] Re: [R390] R390A trimmers

[Graham Baxter]

Hi David,

I suppose paxolin is SRBP, synthetic resin bonded paper.


The little three legged clip is easily removed by placing a jewellers
screwdriver under it close to the pip, and then gently turning it.
This jacks the clip out of its hole and slides it out of the groove in
the rotor shaft in one operation.

The rotor then can be lifted (falls) out.

If the disk and rubber are still bonded to the paxolin, resist the
urge to lever them off. I think it is better to soak them off.

One substance that definitely seems to unbond them is aerosol switch
cleaner. I have learned that if they are still stuck, any attempt to
lever them free will result in a broken disk. But a good soak in
switch cleaner softens the glue without dissolving the silver ink. I
then washed all the parts in alcohol.

Good luck

Graham
G8OAD

On 16/08/07, David C. Hallam <dhallam at rapidsys.com> wrote:
> Graham,
>
> Can you translate paxolin to US English?
>
> I am having a devil of a time with trimmers in a 75A4 and have about decided
> I am going to have to take them apart.  A job I dread.
>
> David
> KC2JD/4
>
> > -----Original Message-----
> > From: r-390-bounces at mailman.qth.net
> > [mailto:r-390-bounces at mailman.qth.net]On Behalf Of Graham Baxter
> > Sent: Thursday, August 16, 2007 4:06 AM
> > To: r-390 at mailman.qth.net
> > Subject: [R-390] Re: [R390] R390A trimmers
> >
> >
> > I did manage to get all the trimmers working again. The problem was
> > that the lower ceramic disk was no longer anchored by the rubber to
> > the paxolin. I dismantled the trimmers and washed them in alcohol. I
> > also polished the silvering where the spring contact will press. I was
> > then able to reassemble them using a spot of cyanoacrylate adhesive
> > either side of the rubber. This has worked well. One of the trimmers
> > had a broken ceramic disk. I reassembled this with cyanoacrylate glue.
> > I bridged the crack on the silvered part by soldering a piece of
> > copper foil across it. I would have liked to use conductive silver
> > paint but I didn't have any. This trimmer at least is scheduled for
> > replacement when I have spares.
> >
> > I found my 9MHz crystal was poor. I tried a cheap HC47 wired crystal,
> > just poking the wires in the holder, and it worked fine on 7, 15 and
> > 24 MHz. So I opened the old crystal, removed the blank and replaced it
> > with the entire new crystal. I replaced the can and it looks great.
> > Interestingly there was a tiny fracture at the edge of the old blank.
> >
> > R390A s are not so common in the UK. I am fortunate to have a couple
> > of friends who are enthusiasts. As well as two EACs I also have a
> > Racal 1772.  It is good but not as good as an on-song R390A.
> >
> >
> > Thanks for your interest
> >
> > Graham
> > G8OAD
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