[TenTec] Omni6+ (564) intermittent problem

[Jack Mandelman]

The Omni6+ intermittent problem that I posted on Friday Aug 8 appears to 
be fixed.

FWIW, on Monday I removed the plate on which the NB and FM boards are 
mounted, to access the XTL osc/L.O. board.  All cables to the XTL 
osc/L.O. board were then disconnected and the board was removed.  I 
should add that before removing the NB and FM board, I verified by scope 
that the L.O. ouput for 15/12M was indeed intermittent.  All solder 
connections associated with the shared 15/12M L.O. output filter were 
then reflowed.  Although several of the solder joints looked suspicious, 
I couldn't positively identify any cracks or opens.

Since the radio has been operating flawlessly all week since I did the 
work, I'm hopeful that the reflow operation fixed an intermittent solder 
joint.  Although at first I was a bit apprehensive about working on this 
buried board, TenTec's excellent labeling of cables and connectors 
quickly relieved my fears.  I took photos along the way, but found that 
they were not required to put things back together again; the pictures 
in the manual were sufficient.

Jack K1VT


______________________________________________________

To: <tentec at contesting.com> Subject: [TenTec] Omni6+ (564) intermittent 
problem From: "Jack Mandelman" <modeler at bellsouth.net> Reply-to: Jack 
Mandelman <modeler at bellsouth.net>, Discussion of Ten-Tec Equipment 
<tentec at contesting.com> Date: Fri, 8 Aug 2008 20:14:55 -0400 List-post: 
<tentec at contesting.com">mailto:tentec at contesting.com>

The other day I decided to check for propagation on 15M, and was
surprised by how unusually quiet the band sounded; even the infamous
21.333MHz birdie was not to be heard!  I then discovered that the
maximum key down power output was about 2 watts, with very little
sensitivity to RF output control setting.  12M exhibited the same
symptoms, but the 564 operated normally on all other bands.  After about
15 minutes the receiver abruptly returned to life and TX output was
normal, on both 15M and 12M.  This intermittent was repeatable for every
one of the several times I checked the rig from a cold start.  The
problem has not been observed after the rig is warmed up.

Based on the symptoms and examination of the schematics, I suspect an
open in the bandpass filter for the L.O. output on the XTAL osc/L.O.
mixer board.  12 and 15 meters share the same filter for the L.O. output
before L.O. signal is sent to the BPF/front end board.  The symptoms may
indicate an open in this filter.  I expect that the switching diodes
(D38 and/or D43) to the filter are not blown, since diodes usually fail
permanently in an open or shorted condition; an intermittent internal to
a diodes is very rare.  I would like to reflow all the solder
connections associated with the L.O. filter served by these diodes.

My question is how to best access the XTAL osc/L.O. mixer board.  Has
anyone had experience with accessing and removing this board?  I believe
it is under the FM and LL driver/NB boards.  Haven't yet removed the
covers to look at this problem. When I do, I will take many photos of
the disassembly along the way.

All comment/suggestions are appreciated.

Jack, K1VT