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

[Craig C. Heaton]

Roger,

I don't think it was crud. When I brought the Amelco home in 2006 and
recapped the beast, the crystal calibrator section never worked correctly.
In trouble shooting it, I swapped crystals, the entire oven, and tried a
crystal that someone sent me. De-Oxit was applied to the pins. Nothing is
impossible, but dirty pins on the crystal or oven are highly unlikely. Must
of pulled it out a dozen times! Also had the original crystal pop out of the
heater as I was prying on it. Bounced on the floor a couple of times, and
rattled ever since. Done broke it. 

Those that have recapped the RF section know there are two BBOD's in the
crystal calibrator section, but are connected to the heater element of the
oven. Kinda hard to mess things up. I looked for hours trying to find any
passive components touching, wires rubbing, etc., before warming up the
soldering iron. 

My guess it was a combination of things. There is a 1meg ohm resistor
paralleled across a 15pF silver mica. Its value had drifted to around 1.5meg
when hot, dropping in resistance as the circuit cooled. A couple other
resistors had increased 20% or more. Then R235 was just plain wrong, but has
no bearing on the oscillator circuit.

What I don't understand is why the new crystal from International Crystal
Manufacture doesn't work in the Amelco, but in the Motorola it functions
just fine???????????My guess is not too many people get enough practice
making crystals of that type, and I was sent one that is just border line.
Just, almost, good enough to be sold for $104.00 US dollars. They made one
and they sold it, hoping it would work. 

I have no way of testing what they sent, but bet there is someone that has
the equipment and/or the experience to do so.

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: Sunday, August 03, 2008 10:34 AM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] Need value of R235 from a RF deck

Craig,

So are we going to write this one up as no trouble found?

Just crud on pin and plug contacts and after enough parts are pulled and 
replaced, enough crud gets displaced to return the circuit to operation.

Another routine R390/A problem.

Roger AI4NI

P.S. It sure was fun while it lasted. Maybe not for you Craig, but I'm just 
looking on.   </HTML>
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