Al -
There are two PLL's in the TR-7, one for the bands below 20M and another
for bands above. Your 'high band' VCO is not locking. The 'wandering'
frequency is just the free-running VCO going to it's 'idle' frequency
'or so', which should be around 32 MHz.
First suspect is corrosion on the card connector pins, and of course all
the likely candidates are UNDER the DR-7 board. Get a bottle of DeoxIT
D100L, and set aside an afternoon to remove, DeoxIT and replace all the
boards. It doesn't hurt to twist each of the coax cables a bit at each
termination. If you unplug one, be careful to get the center conductor
(contact 'pin') aligned carefully before pushing it home. Careful also
to get the DR-7 pins nice and straight to ensure they go into the
correct socket.
If that doesn't take care of it, (~95% probability that it WILL,) then
check the +24 VDC supply on the small power supply board just behind the
front panel logo. Careful to not bump the trimpots, especially the
right-most one closest to the side panel. If this voltage is low,
verify that the top half of the DC-DC converter transformer on that
board is in place and firmly in contact with the lower half. Two 'E'
shaped cores, 'face-to-face' and in firm contact. The shorted loop of
wire around the transformer IS supposed to be there, not to hold the
halves together (wrong axis anyway!) but to minimize the external field
from the transformer.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Al Ward wrote:
Hello to the group
My TR-7 local oscillator for bands 20M and above will not lock. The
display shows it wondering up in frequency. The last band position
that works properly is the 7 MHz position and you can step the
frequency segments up to 10 MHz and that is as high as it will go and
stay locked.
Does anyone have any advice on what and where to look for the problem?
I did buy some extender boards in preparation to work on this problem.
Thanks and 73
Al W5LUA
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