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
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