I just wanted to let you know I managed to get the high VCO
working. I was removing transistors and checking them on my
tester, and when I removed Q504 and noticed that the Gate lead was
broken off half way down to the board. I tested it and it was okay
so had thought I had done that so I put it back in and soldered
the lead together. Put the radio back together and decided to see
what the DR7 readout said and the radio happened to be on the 10
meter band and it was showing the correct frequency. Checked 15
meter and that was working as well. I still have one problem but
will post later on that. My thanks for all the help on this
problem to everyone.
Jim VE1RB
?
On 2025-01-01 20:17, Jim Harris via
groups.io wrote:
toggle quoted message
Show quoted text
Yes Gary that does interest me a lot. We will talk
about that and make a deal I hope. Many thanks for the offer.
Jim VE1RB
On Wed, Jan 1, 2025 at 5:33?PM
Gary Follett via <xntrick1948=
[email protected]>
wrote:
You know, the VCO board in the TR7 is the same as the one
in the R7. I happen to have a working R7 VCO board if this
interests you.
Gary
W0DVN
Okay
I will get it out and have a look see.?
Jim
VE1RB
On Wed, Jan 1,
2025 at 5:28?PM Gary Follett via
??<xntrick1948=
[email protected]>
wrote:
Well, your 30 MHz scope is not entirely
useless. Even though the ~80 MHz VCO will be
severely attenuated, you should still be
able to see it and determine what it looks
like That VCO signal is pretty stout at the
point at which you are observing it (several
volts per to peak).
Gary
W0DVN
Gary
the frequency counter is hook to
5/24. I will check the input to
the two 5 volt regulators and let
you know. I do have ?a scope but
it only goes to 30 mhz but I know
where I can get a good 100 MHz
one. Will get that as soon as I
can and have a looks at those
outputs. Many thanks Gary for all
your help otherwise I would be
working in the dark.?
Jim
VE1RB
On Wed, Jan
1, 2025 at 4:45?PM Gary
Follett via
??<xntrick1948=
[email protected]> wrote:
If that oscillator is
showing anything real (~152
MHz) then it is being
selected. This selection is
enacted by the application
of +10 volts on U502. The
VCO board has no other
information about the band
selected by the band switch.
The only other
information the VCO gets
from the outside world
comes in via pin 5/9 (500
KHz Reference) and pin
5/11 (this is roughly 500
KHz as well, and is the
result of the 40 MHz
Reference, the PTO and the
VCO signal divided by N (N
being the selected number
produced by the band
selection logic) and this
is the signal that closes
the PLL loop.
However, even with the
loop open and unlocked,
the frequency at the
output of the VCO should
never exceed 80 MHz,?
Where are you
measuring the 152 MHz?
If grounding RFC505
on the away end does
nothing, try grounding
the other end. If
still no change, then
ground the physical
junction at CR511A, B
and CR510 A,B. This
should pull the
frequency down a lot.
If not, ground the
Drain of Q504 through
a capacitor of about
0.01 uF. That should
clearly kill any
oscillation and remove
any output from the
VCO.
Then humor me on
this one - measure the
voltage on the inputs
of both 5 volt
regulators U501 and
U502 when a low band
(less than 15 MHz) and
a high band (greater
than 15 MHz) are
selected by the band
switch. If there is a
switching issue,
perhaps BOTH VCO¡¯s are
on when High Band is
selected. I would have
a hard time deriving
what would happen in
this condition but I
am quite sure things
would not go well.
This is when an
oscilloscope would
be handy. You could
look at the waveform
at the output of the
VCO, at pin 5/24,
the output of the
VCO to the radio.
You should see ?a
nice sine wave of
roughly constant
amplitude when
either VCO is
selected.
Gary
W0DVN
Gary
I tried that
ground on
RFC505 and no
change. Is it
not getting
band
information?
Jim
VE1RB
On Wed, Jan 1, 2025 at 3:02?PM Gary Follett via
??<xntrick1948=
[email protected]>
wrote:
If you
are reading
152 MHz, the
you should
ground RFC505
on the end
away from the
varactor
diodes. The
frequency
should come
down.
Gary
W0DVN
Jim
maybe this
will help. I
touched up
several solder
joints
although they
didn¡¯t look
good but not
cracked. I
switched the
input to the
counter and it
is reading 17
to 18 mhz
?
<IMG_1166.jpeg>
as the
frequency is
jumping around
so is not
locked. I
wonder if that
is a clue??
Jim
VE1RB
On Wed, Jan 1, 2025 at 12:52?PM Jim Harris via
??<radiove1rb=
[email protected]> wrote:
Good
ideas Jim and
I will get at
doing that
today. It is
windy and
raining here
quite hard. A
good job
inside hi hi.
I will let you
know how it
goes. Many
thanks for the
suggestions?and help.
Jim VE1RB
At this point
I am
suspicious of
that 1.3 MHz
reading. That
may be a
spurious
reading. It
seems to me
that the VCO
should not be
able to run
there. What is
the level of
the signal?
The frequency
determining
components are
L502 and the
varactor
diodes. Resist
the temptation
to try to
adjust L502.
As a long time
tech told me
back in the
dim past, when
you have a
failure "it is
never the
alignment".
At this point
I think I
would inspect
the solder
connections in
the high VCO
circuit under
magnification
and good
lighting. You
could have a
failed joint
or via. Check
the voltages
on the three
JFETs. C156 or
C517 could be
suspect. You
have a working
low VCO to
compare
voltage and
resistance
readings to.
On Wed, 1 Jan
2025 07:41:18
-0400
"Jim Harris
via?" <radiove1rb=[email protected]> wrote:
> Yes Gary
I did the
ground on
RFC505? when
looking at the
frequency on?
> the
counter and it
does drop a
lot. So I
guess you are
saying the
High?
> VCO is
oscillating at
1.3 MHz . If
that is the
case there
must be?
> something
wrong on that
board unless
the info it
gets is wrong.
Hope?
> this
helps.
--?
73
-Jim
NU0C
