Clarifier unlock for a Kraco KCB-2340 23 channel radio?

[doffo]

Hello,

I was hoping someone would know how to get the clarifier unlocked on this old Kraco KCB-2340. Tried to do some searching but couldn't find much information on it. I do see just 2 wires going up to the clarifier, so hoping there is a way to just get the TX to follow. The board is a Cybernet PTBM034AOX 23 channel radio. The 2 wires that come off the Clarifier, the one goes up front to the 1st shorter board, and the 2nd wire goes all the way back near the Relay.
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Update:
Tracing some stuff down, the yellow wire coming off the clarifier has voltage to it, and the red wire that goes all the way back to the relay seems to not have voltage. When you key it, the voltage at the yellow wire up front goes to 2.54v. Unsure what is regulating the voltage when it gets cut off.

I dont think its as easy as removing the ground from the relay and permanently putting to ground, but hope this helps in tracking on how to unlock the clarifier.
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Here are a few pictures of the area:



Appreciate any help on this. Hoping it can be done without too much trouble.

 

[TM86]

Attaching a PDF of the owner's manual so you'll have a schematic. Schematic shows three wires to the clarifier control, one for RX, which you already found, and one for TX, which is supposed to connect to a fixed point of resistance in the clarifier control, and then one that goes to the varactor in the 14 MHz oscillator.

No idea why you only found two wires going to the clarifier pot. From your description it sounds like the TX side fixed resistance is still there. I've got a PTBM035COX radio that has a similar clarifier circuit. There are two wires going to the normal two out of three terminals you'd expect to see on any potentiometer, and then another contact sticking out the other side of the pot that a third wire goes to. Perhaps your radio has something similar?

 

[doffo]

Attaching a PDF of the owner's manual so you'll have a schematic. Schematic shows three wires to the clarifier control, one for RX, which you already found, and one for TX, which is supposed to connect to a fixed point of resistance in the clarifier control, and then one that goes to the varactor in the 14 MHz oscillator.

No idea why you only found two wires going to the clarifier pot. From your description it sounds like the TX side fixed resistance is still there. I've got a PTBM035COX radio that has a similar clarifier circuit. There are two wires going to the normal two out of three terminals you'd expect to see on any potentiometer, and then another contact sticking out the other side of the pot that a third wire goes to. Perhaps your radio has something similar?

I looked again at the potentiometer, and its only the 2 wires. It still seems that the red wire is going directly to ground, and when you transmit it disconnects it.

I will have a look at the other model you have and see how close they are. Thanks.

 

[NZ8N]

 

[doffo]

View attachment 70459

I seen the area, but I am not sure what to break or disconnect... But like on my radio, it only had the 2 wires connected.

 

[NZ8N]

Ground the RX side of that section of the relay, disconnect the TX side.

Or, unsolder the Red wire back at the relay, solder it to Ground.

 

[doffo]

Ground the RX side of that section of the relay, disconnect the TX side.

Or, unsolder the Red wire back at the relay, solder it to Ground.

Soldered the wire straight to ground, but that hardly makes any changes during transmit. Nothing even noticeable when you adjust the clarifier potentiometer.

 

[brandon7861]

There is a pink wire to investigate. The schematic in the manual TM86 shared has writing in it that shows numbers by the clarifier wires that I assume correspond to the numbers on the board by the relay. This writing could be wrong, but nonetheless, I would like to know where the pink wire goes. Your image shows the yellow wire coming off R205, which should go to the relay center contact.

There are a couple things standing out. If the numbers in that schematic are correct, the yellow wire is may be going to the wrong relay terminal. It also appears that the yellow and pink wire have been removed and re-wrapped on their pins. Something may have been switched around.

Edit: what NZ8N said should have worked even if things at the relay are messed up, so I don't know. Tying that red wire to ground should make RX and TX the same.

 

[brandon7861]

ok... lets say that they didn't have one of those side-tapped pots and had to improvise.

If the TX side of the relay went to the node at R205/R206/R208 via fixed resistor to the back side of the board (where we can't see it in the pics), where the yellow wire comes from, grounding the red wire wouldn't take the TX resistance out of circuit, and it would remain in parallel with the clarifier control even after the recommended change. Clipping the TX wire on the relay may be necessary to take whatever that goes to out of parallel during TX.

 

[doffo]

ok... lets say that they didn't have one of those side-tapped pots and had to improvise.

If the TX side of the relay went to the node at R205/R206/R208 via fixed resistor to the back side of the board (where we can't see it in the pics), where the yellow wire comes from, grounding the red wire wouldn't take the TX resistance out of circuit, and it would remain in parallel with the clarifier control even after the recommended change. Clipping the TX wire on the relay may be necessary to take whatever that goes to out of parallel during TX.

Thanks for the tips. Once I get some stuff done this AM I may try that. Only thing that I could think of see where the board gets the voltage from once the clarifier wire is off. This way, you can grab the 5v and feed it into it using the clarifier to that spot... Just thinking out loud.

 

[Ez2cDave]

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