[R-390] Need value of R235 from a RF deck

[Craig C. Heaton]

Replaced about 5 silver micas this evening. Will double check my
wiring/soldering in the morning. 

Going to check the circuits in the morning with a frequency counter & scope.
Might be able to narrow the problem down to the 200KC circuit or the
multivibrator.

Note: one of the silver micas (15pF) had a crusty coating on one lead. I've
tried to remelt most of the solder joints, but this cap was in a position
hard to reach. Had to remove other components to replace it. That's when I
found the crusty coating. Don't know if the solder area was clean, it was
damned hard to remove! It's clean now.

Craig,



-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Flowertime01 at wmconnect.com
Sent: Tuesday, July 29, 2008 4:12 PM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] Need value of R235 from a RF deck

Craig,

I understand that you believe the problem is in fact the crystal cal 
oscillator shifting to some new frequency every time you switch the function
switch to 
CAl.

Ed W2EMN put in some good thoughts on the crystal contacts. 

Remember the crystal oven is also a plug in device. You may want to check
the 
octal socket contacts under the oven can and the crystal contacts in the
oven 
can also.  And as long as you are checking contacts do the tube socket pins 
also.

I think the variable cap is good as you describe it.  As you get two null 
points, you are not out beyond the limit of the cap to yield a proper
adjustment.

Once you get past the easy mechanical ground tie points and socket points
and 
do not cure the critter, you may have to go looking for bad solder joints in

the circuit.

Something is changing resistance and or capacitance in the circuit as it get

switched on each time.

Eye ball the resistors real close. Finding one that flakes under load is a 
real challenge for test equipment. You almost have to get luck with an eye
ball.

I would hate to think you have to live with this problem until it goes to 
failure so you can find it.

If the deck is still open and you have not done it yet, eye ball the RF band

switch contact mesh and make sure it is in its best alignment through all
the 
band stops and on each wafer switch section.

Are you getting any direct mail with additional ideas?

Let us know what you are finding.

Thanks for sharing with us.

Roger AI4NI

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