[Premium-Rx] WJ 8617 Synthesizer Problem SOLVED

Mon Oct 12 12:51:25 EDT 2009

Rye:

Just like us. We need a kick in the tail to get us back moving again.

Michael C. Martin
Roi-Namur, KWAJALEIN ATOLL
CMR #702 PO Box 8211 
APO, AP  96557-0003

Don't worry about the world coming to an end today.
It's already tomorrow in The Marshall Islands.

From: Rye Gewalt [mailto:ryerson at bellsouth.net] 
Sent: Tuesday, October 13, 2009 4:37 AM
To: premium-rx at mailman.qth.net
Cc: 'Steve Pappin'; 'David Schofield'; 'sigintdf'; 'Michael Martin - Roi-Namur, Marshall Islands';
jmcvein at teleport.com
Subject: Re: [Premium-Rx] WJ 8617 Synthesizer Problem SOLVED

Thanks to the encouragement and advice from several individuals on the list, my WJ 8617B is working
again  As I suspected - and others confirmed - the problem was with the 2nd LO.   Specifically the
4.4 to 5.5 MHz VCO which was out of lock  -- probably due to component drift over the years.  This
seems to be rather a common condition.

The most daunting problem was getting the assembly out of the receiver and wired back into operation
laying outside of the chassis.  I am fortunate to have the maintenance  tool set that includes two
coax extender cables and that solved the problem.  

I used the very helpful VCO Alignment  Process  by Spencer Bahner to give me courage and make the
actual adjustments.  It's somewhere around here on the net, but I can't seem to find the link at the
moment.  It's a necessity...

As suggested, capacitor C7, a very (very) small piston cap, that sets the center frequency of the
VCO needed adjustment.  It took almost two turns to get everything back in operation.  

My radio is probably newer production (CA 1987) and  it has several features that seem a bit
different from some of the units discussed on the list.  

It has a test point (E2)  on the top of the box for measuring the loop control voltage - some don't
have this feature.

There is a hole in the bottom of the box to allow C7 to be adjusted.   HOWEVER, it is almost
impossible to get the adjustment tool  into the tiny slot on the recessed capacitor working blind
through the hole  --  so it makes sense to try to do the adjustment with everything outside of the
receiver with the cover removed.  Even then it is hard to get the screwdriver into the slot of the
piston capacitor unless you look closely or have a very sensitive feel.  Once the VCO is adjusted
for 7.2 volts on the test point, putting the cover back on changes the voltage appreciably and you
have to do some trial and error adjustment until the voltage is at the correct point with the cover
on.   (The VCO runs at 500 MHz)

There doesn't seem to be much discussion about the two LEDs on the board .  The LEDs can be seen
through two holes in the top of the box when it is slid partly out the receiver.  These appear to be
a VCO setup tuning aid  -- or maybe just an out of lock indicator.  If either LED is lit, the loop
is out of lock.  One LED indicates that the VCO is out of lock and at the high end of its tuning
range  -- while the other indicates that the VCO is  at the low end of its tuning range and out of
lock.  Adjusting the capacitor so that both LEDs are off would seem to be a first step in setting
the VCO, but getting it set to precisely  7.2 volts (the nominal middle if its tuning range) seems
to assure it won't go out of lock when tuned to max or min frequency.

Be sure to check that the VCO stays locked when at the high and low limits of its range (20/21 MHz).
If it doesn't you probably have to adjust the center 'voltage' to accommodate the tuning range.   I
guess some receivers run at about 5.5 volts..

A note on the tuning tool that I got with the maintenance kit.  It is marked Sprague Goodman JFD
5284.  A quick look at their web page indicates that a similar tool is still available (JFD 5284Z).
http://www.spraguegoodman.com/206/206p1.html   If you want to make a tool, the metal blade is .015"
thick, .100" wide and .064" long and is imbedded in a plastic rod that is about .100" in diameter.

I have pictures of a lot of this activity and if anybody is interested I would be happy to email
them.

Thanks again to all of the helpful people on the list.   I wouldn't have had the courage to dig into
the radio without your help.

Regards
Rye
K9LCJ since 1957

My words mean exactly what I want them to mean, neither more, nor less.   Lewis Carrol