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Dx2547

kaos513

Sr. Member
Apr 10, 2014
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Putnam county,NY
Hello guys I ran into an issue with my dx2547 alignment for vco connect freq to tp6 when I do numbers jump around on tx mode but here is wierd part on tp5 alignment for vco on all bands work to adjust don't really know what tp6 does unless vco went bad ? Thanks
 

nomadradio

Analog Retentive
Apr 3, 2005
5,672
8,442
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Louisville, KY
www.nomadradio.com
TP5 and TP6 are not connected to the VCO, or any other part of the radio's PLL section. These two test points are for the carrier oscillator, 10.695 MHz plus or minus 2.5 kHz.

This is a bit tricky. Hooking a probe to these points tends to disrupt the circuit. You could try probing the emitter of Q46, the carrier oscillator transistor. Just one problem. The tip of the probe has capacitance to ground. This will alter the frequency coming out of Q46 when the probe is disconnected. The test points shown are isolated from the crystal and Q46, but the level is really low. Only a counter with a really sensitive input will get you a reading from those.

We use either a service monitor's receiver input or an accurate ham transceiver to 'sniff' the output from this crystal without tapping into the circuit with a probe. This way it gets set on frequency without any disruption to the setting of the trimmer slug for each mode.

One way to minimize the disruption to your counter reading when in transmit mode is to remove the bias-test jumper (mirror board) while trying to get a counter reading in AM transmit. Stray RF from the final stage will leak into your counter probe and disrupt the reading. Removing that jumper while setting the 10.695 MHz AM carrier-frequency adjustment might fix your issue.

73
 

nomadradio

Analog Retentive
Apr 3, 2005
5,672
8,442
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Louisville, KY
www.nomadradio.com
There is a small-value capacitor between the carrier oscillator and TP6. Odds are that your probe has too much capacitance to ground from the probe tip. This creates an AC-voltage divider that cuts the signal level below the minimum for the counter.

73
 
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nomadradio

Analog Retentive
Apr 3, 2005
5,672
8,442
573
Louisville, KY
www.nomadradio.com
All frequency counters will require some minimum input-signal level to show a stable count. When the level is below that threshold, the digits will typically be unstable, or simply read zero.

They're not all created equal on this count. Some are more sensitive than others.

73
 

sonoma

Sr. Member
Sep 14, 2005
2,105
937
123
oklahoma
I have one counter that will act up like yours on certain radios. I put about a 68pf cap on the center lead of the probe and in most cases it will start reading as it should. some times I have to play with the cap as far as what pf it is. 30 to 80 or even 100pf have worked for me. I have a couple freq counters that this does not happen to but the one will almost always do that on a lot of the ranger or galaxy radios.
 

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