Electronics > Repair

Boonton 41-4B power sensor repair advice

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edpalmer42:
Here's a web page that talks about various RF probes.

https://web.archive.org/web/20110303221109/http://members.shaw.ca/novotill/RfProbeSensorMvUw/index.htm

Note that unlike most probes, ours have the terminating resistors exposed to DC that might be coming from the DUT.  Even if they didn't burn out, thermal cycling could stress the solder joint and cause eventual failure.  I thought that my probe had the resistors protected from DC, but it turns out that I was wrong.  The same failure mode also exists with repeated exposure to high RF levels.

I've also attached a French document that talks about repairing a Boonton probe.

Ed

xrunner:

--- Quote from: Kosmic on October 22, 2023, 05:23:53 pm ---Well, everything is possible if your not necessarily interested in accuracy and higher GHz range.

--- End quote ---

Yea under 1 GHz is pretty much going to cover my needs.  :)


--- Quote ---This guy made his own probe  :)

--- End quote ---

I did see that. Seems to work reasonably well.


--- Quote from: edpalmer42 on October 22, 2023, 07:04:45 pm ---Here's a web page that talks about various RF probes.

https://web.archive.org/web/20110303221109/http://members.shaw.ca/novotill/RfProbeSensorMvUw/index.htm

Note that unlike most probes, ours have the terminating resistors exposed to DC that might be coming from the DUT.  Even if they didn't burn out, thermal cycling could stress the solder joint and cause eventual failure.  I thought that my probe had the resistors protected from DC, but it turns out that I was wrong.  The same failure mode also exists with repeated exposure to high RF levels.

--- End quote ---

I'm sure the sensor I'm dealing with was abused, because I know the ham very well I got it from. He gave me a Boonton Model 42A and the sensor I'm trying to repair. He got them at a hamfest but didn't understand how to use it to test his handheld transceiver, which puts out either about 1 W or about 5 W. I'm pretty sure he zapped the sensor with of of those two power levels because he didn't understand he would need an attenuator, but for how long I'm not sure.  :palm:


--- Quote ---I've also attached a French document that talks about repairing a Boonton probe.

Ed

--- End quote ---

Oh nice thanks.

By the way, does anyone know where I can get the connectors for the Boonton sensor cable (and preferably the correct cable wire also). I want to put new connectors on the cable or build a new one, because the one I have isn't in great shape. I can't manage to find the parts anywhere. I know here it comes ... they aren't available any longer.  :-\

edpalmer42:
Looks like the connectors are available on the standard auction site, but only at the cost of one or two body parts.   :o :wtf:  If you have a strong stomach, search for < Amphenol microphone connector "2 pin" >.  I think that's the right connector, but you should do some further checking.

If you have to replace the cable itself, I think I read somewhere that it's very special.  Due to the very low DC values that will be present at low RF levels, the cable has to be low microphonic, low triboelectric, shielded and yet physically rugged and flexible.  IOW, pure magic!

Kosmic:

--- Quote from: xrunner on October 22, 2023, 07:35:05 pm ---By the way, does anyone know where I can get the connectors for the Boonton sensor cable (and preferably the correct cable wire also). I want to put new connectors on the cable or build a new one, because the one I have isn't in great shape. I can't manage to find the parts anywhere. I know here it comes ... they aren't available any longer.  :-\

--- End quote ---

The connector is Amphenol 80-MC2M. They are not made anymore.



As for the cable it look pretty standard to me (shielded with 2 conductors. see picture below). I made a new one using Canare L-2T2S Audio Cable and could not see any differences in term of performance.


xrunner:


--- Quote from: edpalmer42 on October 22, 2023, 09:19:10 pm ---Looks like the connectors are available on the standard auction site, but only at the cost of one or two body parts.   :o :wtf:  If you have a strong stomach, search for < Amphenol microphone connector "2 pin" >.  I think that's the right connector, but you should do some further checking.

--- End quote ---

Ah thanks I found them on Fleabay - "AMPHENOL 80-MC2M 2 PIN OFF-SET MICROPHONE PLUG FOR COLLINS HEATHKIT BROWNING NOS"

 :wtf: $39 to $50 for ONE? They can shove it where the sun don't shine!


--- Quote ---If you have to replace the cable itself, I think I read somewhere that it's very special.  Due to the very low DC values that will be present at low RF levels, the cable has to be low microphonic, low triboelectric, shielded and yet physically rugged and flexible.  IOW, pure magic!

--- End quote ---

You mean I can't use the roll of old Radio Shack speaker wire in my junk box?  :-DD


--- Quote from: Kosmic on October 22, 2023, 09:42:22 pm ---The connector is Amphenol 80-MC2M. They are not made anymore.

--- End quote ---

That's what I was afraid of, and I'm also afraid of NOS prices.  :(


--- Quote ---As for the cable it look pretty standard to me (shielded with 2 conductors. see picture below). I made a new one using Canare L-2T2S Audio Cable and could not see any differences in term of performance.

--- End quote ---

I could just unsolder the connector pins, clip back the cable a few inches past where it's been flexing for 40 years, and make it all back up again. I did see that brass ferrule that is crimped on the braid. I doubt I can use it again. I'll have to figure out to get a good ground from the shield to the connector housing. Do the two signal wires also have their own shield and are these shields tied to the main outside shield?

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