Author Topic: Boonton 41-4B power sensor repair advice  (Read 5213 times)

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Online xrunnerTopic starter

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Re: Boonton 41-4B power sensor repair advice
« Reply #25 on: October 25, 2023, 10:03:39 pm »
Do you have access to a VNA?

Yes I do.  :)

Quote
It would be interesting to see what the impedance of your rebuilt probe looks like compared to an official one.

I wish I'd have documented it before it failed. However I have another Boonton sensor model 51010 (4A), I can check the response of that sensor. Or do you have one closer to the 4B that I can compare to?

You see the model 4220 meter I'm using. I got the meter for a steal from Fleabay a couple of years ago because I couldn't repair the abused Boonton Model 42A Microwattmeter the ham gave me with the sensor.

Quote
I think that's the purpose of the offset washers that the resistor leads were clamped under.  By turning the washer you could tweak the termination.

Ed

Oh really that's interesting. I just thought the washers were a secure method of holding the wire. The offset of the washers provides a little spring to the area so if the screw ever got a bit loose the connection would still be tight. But hell if I know you are probably right.


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Offline edpalmer42

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Re: Boonton 41-4B power sensor repair advice
« Reply #26 on: October 26, 2023, 01:27:41 am »
I don't have anything that could make those kinds of measurements at the high frequencies that would be necessary.  For all I know, you might need to step up to one of the 18 GHz probes to see any effect from turning the washers.

Your cable looks a lot different from mine.  I've got two cables and both of them are almost perfectly round rather than wavy like yours.  One of mine has Amphenol connectors and the connectors on the other one are labelled 'KINGS1-1464'.  Unfortunately, it looks like that's the part number for the rubber strain relief.  Kings is a well-known manufacturer of high quality RF connectors.  Neither cable has any labelling on the cable itself.
 

Online xrunnerTopic starter

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Re: Boonton 41-4B power sensor repair advice
« Reply #27 on: October 28, 2023, 10:53:04 pm »
Well that was fun.  :P

I got the 160 ohm SMD 1206 parts. I cobbled together a helping hands holding tweezers to hold each part at the right angle. I then soldered the two diodes and two 160 ohm resistors in place like the original parts were.

It sure looks like it's working - it zeros and calibrates great and no strange noisy tantrums.

I need to test it at more power levels and frequencies which I'll do in the next few days using my Agilent 8648A. Of course I can't compare it directly to the original sensor response now. But I do know during the periods when the original was working, it was only a few tenths of a dB off from the setting of the Agilent over it's power range.  I'll report those results here.
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Offline edpalmer42

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Re: Boonton 41-4B power sensor repair advice
« Reply #28 on: October 29, 2023, 02:49:30 am »
Looks good, xrunner, but I have to admit that I'm worried about those surface mount resistors.  They have no physical strength so a single thump could crack one or more of them.  It should be okay if you're careful, but you could also consider something like a blob of silicone to provide some support by 'glueing' the resistor to the main chassis.  I don't think that would affect the readings, but YMMV.

A radical thought just occurred to me.  Imagine taking a tiny piece of PC board with just enough copper traces to allow you to solder the resistor and a wire at each end.  Maybe a prototyping strip board.  The board would remove almost all the stress from the resistor.  It would be like converting a surface mount resistor into a leaded resistor.
 

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Re: Boonton 41-4B power sensor repair advice
« Reply #29 on: October 29, 2023, 12:00:04 pm »
Looks good, xrunner, but I have to admit that I'm worried about those surface mount resistors.  They have no physical strength ...

Oh now ... it's not true that they have no physical strength. They have a physical "strength" x greater than zero and less than Max. We don't know what "x" is. How hard is it to crack one in two? I have no idea but they don't seem too frail. I've held them with small pliers and tweezers and they don't seem delicate for their size at all.

But were using subjective terms here, so I don't know. I mean, look how the original parts ended up. The red resistor (100 ohm) cracked off at the end on it's own, and I said the 160 ohm just crumbled when I barely touched them and they aren't SMD. That's how Boonton engineers decided to mount those parts. 30 years from now if they break I won't care because I'll be long gone and this meter will either be in a museum of ancient technology or a landfill (which is where it will end up if my family members get hold of it).  :-\

But I'm not worried really. This thing ain't going into the Gaza strip to check transmitters. Remember I made a custom mounting for the 100 ohm that use the copper sheet strips. I specifically made the strips to bend a bit using a little curved spring at one end.

Look at this. I was searching Fleabay for Boonton cables and found this item -

eBay auction: #186114963838

A 41-4B sensor and cable for $60. But one of the connector pins has nothing inside. How well do you think it works? The parts are listed as used which means they works correctly but it's not new. I messaged the seller but no reply yet ...

 :popcorn:
   
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Offline edpalmer42

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Re: Boonton 41-4B power sensor repair advice
« Reply #30 on: October 29, 2023, 05:51:18 pm »
A 41-4B sensor and cable for $60. But one of the connector pins has nothing inside. How well do you think it works? The parts are listed as used which means they works correctly but it's not new. I messaged the seller but no reply yet ...

 :popcorn:
 

That could be fine.  It likely means that when it was soldered at the factory, the solder didn't run down far enough to plug the end of the pin.  I'm not aware of any requirement that the wire itself has to go right to the end of the pin.  If I was looking for a cable I'd grab it and inspect it on receipt.  Worst case, you're just resoldering the end of the cable.

Ed
 
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Online xrunnerTopic starter

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Re: Boonton 41-4B power sensor repair advice
« Reply #31 on: October 29, 2023, 11:30:45 pm »
Here's the initial checkout of the repaired sensor. It's working about the same as it was before (whenever it decided to work for a bit). The Agilent 8648A has a stated amplitude accuracy if +/- 1 dB, although I know from many different comparisons of power meters over the years it's more accurate than that, more like tenths of a dB.

On the +10 dBm setting I do know the output is always a little less accurate than the lower ranges (but still within specs) so the Boonton is reading correct there also.

PWR   1 MHz   100 MHz   1 GHz

+10   +9.7   +9.7   +9.5
   0      0.0    0.0       0.2
-10   -10.1   -9.9    -10.1
-20   -20.1   -20.1   -20.2
-30   -30.2   -30.1   -30.2
-40   -40.1   -40.1   -40.3
-50   -50.0   -50.0   -50.2
-60   -60.2   -59.9   -60.4
   
Oh I forgot to test the input impedance, I'll do that next.
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Offline ch_scr

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Re: Boonton 41-4B power sensor repair advice
« Reply #32 on: October 30, 2023, 08:16:33 am »
Looks good, xrunner, but I have to admit that I'm worried about those surface mount resistors.  They have no physical strength ...

Oh now ... it's not true that they have no physical strength. They have a physical "strength" x greater than zero and less than Max. We don't know what "x" is. How hard is it to crack one in two? I have no idea but they don't seem too frail. I've held them with small pliers and tweezers and they don't seem delicate for their size at all.
(...)
From my experience, what breaks (or rather rips off) is usually the metallized termination on the ends, not the ceramic carrier itself. The lever on the metallized end is quite large if you have the part soldered down to something solid with it's end sticking up.
In a carefull home shop you should be fine with it, but if one were to knock this around daily I'd guess one of them might break from the shock loads, from the looks I'd mostly be worried about the ones going to the diodes, with their rigid mounting on both ends. Would be interesting to mount this to a shaker table to see what actually breaks  :-DD
I suspect mini- or microMELF components to be more rigid (regarding their terminations especially) than flat SMD's and that might make them more suited for such a repair.
With all that said, good job on the repair nonetheless!
 
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Re: Boonton 41-4B power sensor repair advice
« Reply #33 on: October 30, 2023, 06:18:18 pm »
With all that said, good job on the repair nonetheless!

Thanks for your comments.

Here's a microscope pic of several items for comparison.

From top to bottom -

SMD 1206 zero ohm
original 100 ohm Boonton part
Same as above
original 160 ohm Boonton part

The 1206 part is very close to the same length as the resistors, which is the reason I chose that dimension SMD.

The original problem was that one of the 100 ohm parts (red part) was cracking loose right at the solder joint. Why this happened we can't say for sure. However, these parts are decades old and I'd bet money they haven't been touched or repaired since they left the factory. Only the original damaged part was going to be removed and replaced. However, they were so delicate that they just fell apart at the ends (see red parts in pic). Even the metallic coating came off.

Not to stop there, a 160 ohm part (tan resistor) had one end of it crack off. Basically the sensor was at it's end-of-life. After what - 3 decades, it needed to be re-built or tossed. What caused the degradation in reliability? Was it banged on a table numerous times or were the parts the wrong choice from the beginning (for long-term reliability). I know it was in the hands of Ham radio operators for some time, so draw your own conclusions there.

The point is, the original parts Boonton selected, and the original way Boonton engineers told the assembly line workers to construct the center area of the sensor (the soldering) didn't fare all that well in the long run. What I've done is either going to last for a little while (subjective time) or a long while (subjective time). I don't abuse equipment so I'm guessing a long while (years) but we shall see. I'll test it at least once per year and report if if fails.
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Offline Kosmic

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Re: Boonton 41-4B power sensor repair advice
« Reply #34 on: October 30, 2023, 11:57:05 pm »
A 41-4B sensor and cable for $60. But one of the connector pins has nothing inside. How well do you think it works? The parts are listed as used which means they works correctly but it's not new. I messaged the seller but no reply yet ...

The pins are hollow, and as Ed said, it's not required for the solder to go through up to the tip. As long as the wire is soldered correctly to the pin.

I got some Boonton cables here and some of them are exactly like that.

 

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Re: Boonton 41-4B power sensor repair advice
« Reply #35 on: October 31, 2023, 12:05:21 am »
The pins are hollow, and as Ed said, it's not required for the solder to go through up to the tip. As long as the wire is soldered correctly to the pin.

I got some Boonton cables here and some of them are exactly like that.

I've always seen pins like that with holes at the end soldered at the end and the excess wire cut off afterwards. That's always the way I've done it too, but hey, I haven't seen it all in in this field and never will.

 :-//
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Offline Kosmic

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Re: Boonton 41-4B power sensor repair advice
« Reply #36 on: October 31, 2023, 12:14:35 am »
Probably depend how it's soldered. Heatkit was recommending to have a extra long wire and cut the excess.

 

Offline edpalmer42

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Re: Boonton 41-4B power sensor repair advice
« Reply #37 on: October 31, 2023, 01:41:18 am »
The problem with trying to solder those pins from the end is that it's almost impossible (for me, anyway) to finish the job without getting solder on the outside of the pin.  If that happens, the pin won't fit in the socket so then you have to remove the excess solder and if it takes too long, the plastic holding the pin softens and the pin moves and it still won't fit in the socket and now the plug is ruined and I have to cut it off and start everything from scratch!!!  :palm: :rant:  |O
 

Online xrunnerTopic starter

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Re: Boonton 41-4B power sensor repair advice
« Reply #38 on: October 31, 2023, 01:43:51 am »
OK now I have to ask it ...

If you don't solder it at the end where you can clearly see the quality of the work, then how do you know it's a quality solder job on the inside of the pin down in there.

 :scared:
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Offline edpalmer42

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Re: Boonton 41-4B power sensor repair advice
« Reply #39 on: October 31, 2023, 08:25:46 am »
There are lots of situations where it's difficult or impossible to visually inspect a soldered joint.  You do the best you can with the specifics that you've got, the limitations imposed, and the quality demands that are present.

You might dump the soldered joint and go for a crimped joint, if you can find such a connector.
You might get a roll of super small solder that you can fit through the hole in the end.
You might cut a small piece of solder and shove it into the open end of the pin, then heavily tin the wire, heat the pin, shove the wire in.
You might search for a connector where the pins are removable so you can solder the wire externally without worrying about melting the plastic.
You might inject a drop of liquid flux into the pin to help ensure that the solder wets the surface.

In all of the above, you're working blind.  Being able to see the wire at the end of the pin tells you little about whether you got a good joint or not.

We have to deal with:
- old oxidized connectors vs. new, clean ones
- old solder which, oddly, sometimes doesn't want to melt
- unknown heat resistance of the plastic surrounding the pins

The solution to the problem is critically dependent on whether you're doing a repair or building new or, as in our case, dealing with an almost unobtainium connector.  Remember that the connectors available on the auction site might be NOS that have been sitting around for 20 years.  Solder might stick to the inside of those pins with no trouble or it might be almost impossible to get it to stick.  One brand might work fine while another brand might be a disaster.

This is what you have to deal with when you're working on equipment that's old enough to vote!

Ed
 

Online xrunnerTopic starter

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Re: Boonton 41-4B power sensor repair advice
« Reply #40 on: October 31, 2023, 12:06:46 pm »
Being able to see the wire at the end of the pin tells you little about whether you got a good joint or not.

Well let's move on, but seeing the solder work even at the end of a pin like that is better than not seeing it. Seeing something is better than seeing nothing. That's been my avowed policy for quite a number of years.  :P

Anyways ... here's the input impedance plots from both Boonton sensors I have. The top plot is a Boonton 41-4A which to my knowledge is original and not repaired. The bottom plot is the repaired 41-4B. Smith chart and S11. Draw your conclusions as you will.

 :popcorn:
« Last Edit: October 31, 2023, 09:58:39 pm by xrunner »
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Online factory

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Re: Boonton 41-4B power sensor repair advice
« Reply #41 on: September 22, 2024, 01:52:18 pm »
Another Boonton 41-4B power sensor, this one is a little older than the one repaired in this thread, it came with a 1970s 42AD microwattmeter.

I'm going to need to do some surgery to this one, as there is a short across the input capacitor, this is the one between the 100Ω resistors & the two diodes, to me it looks as if someone made some repairs and accidentally shorted it with solder. It would be interesting to see if anyone else has an older 41-4B & some pictures of the insides for comparison.

The sleeving for one of the output leads needs replacing too, it's worn through where it goes into the connector section, this was intermittently shorting on the casing.

David
« Last Edit: September 22, 2024, 01:55:12 pm by factory »
 
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Re: Boonton 41-4B power sensor repair advice
« Reply #42 on: September 22, 2024, 11:15:01 pm »
This will be a good contribution to the thread. I'll be watching with great interest.  :popcorn:
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