[R-390] R-390 alignment attempt #1, need advice - Crystal Deck

[Roger Ruszkowski]

Frank,
 
You did not mention if this R390 was new to you.
Or had it worked OK in the past.
Or you just do  not know if it has worked in the past.
 
It is fixable.
 
But it is an R390.
 
Getting into the crystal deck of the R390 is more complex than on the R390A.
 
The crystals come un seated in the oven and the terminals pins of the crystals get 
oxidized.
 
And if the receiver was not stored in a heated place and allowed to freeze real good
some of the crystals may have given it up.
 
As long as you have to do this maintenance procedure there is no reason to do only part of it.
 
Your going to have to pull the RF deck and the crystal oscillator deck as a pair.

You are going to have to open the oven covers (two layers) to get to the crystals.
Once you get that far into the receiver you can get to the trimmer caps and the 
big selector switch.

Pull all the crystals and clean (deoxit) the pins and sockets.
Clean up the caps but not necessary to disassemble them.
Clean up the selector switch contacts.

If the missing ones are hit and miss then its likely crystal need sockets and pins cleaned.
If every thing drops out on one end or the other it can be selector switch mechanical alignment.

As long as you have the RF deck out to get to the crystals you should do the whole RF deck 
cleaning and lubrication maintenance and check the RF band switch alignment.

Worry not about that green gear thing its way over rated.
But if you have it use it.
If not you will just have to make sure things are aligned as you reinstall the RF deck.

Then you can put every thing back together and see how many mega hertz bands you recovered.
You can look at the missing mega hertz bands and decide if it a crystal with all of its harmonics missing
or a trimmer cap as some of the crystal fundamentals and harmonics are there.

And see what is still missing then you can swap in some crystals from your spare deck.
Or ask the fellows for some help with the crystals you think you need.

Then you can take it all apart again to install the crystals.

It Is not hard to do. It is  just a slow screw job going both ways and takes time.

Moving these receivers down the road takes out more crystals than any thing.
The crystals just do not like to be bounced around.

Frank if you need some R390 photos put up another post and I will send you some direct
from a R390 rebuild I did a couple years ago.

It could be worth your time to bread board up a crystal oscillator that you 
use to check the fundamental of all the crystals with. Just looking at the output level with a scope.

Trying to match up the  stray capacitance to see if they are on frequency will not be of much value.
The crystals will oscillate or not oscillate.
Once you get a circuit built up that some crystals work in then you can expect that the ones that do not work are bad.

It will be a combination of things. a bad crystal, a dirty trimmer, a loose crystal, an oxidized switch contact.

A good maintenance cleaning will cure every thing except the real bad parts.
And the few problems that remain will be easy to diagnose and resolve.

Roger AI4NI
 
 
-----Original Message-----
From: Frank Hughes <fsh396ss at gmail.com>
To: r-390 <r-390 at mailman.qth.net>
Sent: Sun, Aug 3, 2014 4:39 pm
Subject: [R-390] R-390 alignment attempt #1, need advice - Crystal Deck


Hi,
I went through the first pass of alignment on the R-390, found some things
that need attention, not sure how to proceed.

Section 77 , Chapter 3 "Repairs and Adjustments" in TM 11-5820-357-35.
"Alignment of Second Crystal Oscillator"

Some of the crystals won't adjust w/ the trimmer.

Initially did not think this was important, as they are bands I don't use.

But by the time I got to the RF deck alignment, it became clear that I will
have to fix them.

All the manual says is "If no indication is obtained, check the
"Crystal-oscillator bandswitch".

If the "Crystal-oscillator bandswitch" is the big wafer switch inside the
crystal deck, I might be able to get some Deoxit on the wipers/traces, but
WOW, that thing is buried.

But could the problem also be a dirty trimmer and/or bad crystal?

I have a spare crystal deck to swap parts out of, if needed.

Thanks & 73
Frank
KJ4OLL
______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:R-390 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html