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Repairing a probe X10, X100 Readout Resistor


 

Has anyone ever tried to repair or change the readout resistor connected to the spring pin of a probe’s BNC Connector?

Can it even be done?

 

Dennis Tillman W7PF


snapdiode
 

Great question. Not on my P6105. It's actually kind of baffling how the collet/BNC thingy was made in the first place.
What's your probe's model number?


Brent W8XG
 

I realize this is an old thread, but I've just repaired a p6129b probe. It has a readout pin, but the scope was not seeing it in 10x when the switch was in that mode. (it has the 1x /10x switch). In 1x, the resistor is simply switched out. So, the ring "floats" putting the scope in 1x mode. With the switch is in 10x the little 1/16watt axial resistor (11k - it's in the compensator box) is switched in, resulting in the scope switching it's V/Div values by 10. Mine had quit. I took it apart. There is a very, very fine wire running from the readout pin, thru the resistor, thru the switch, then to the BNC ground. It's tedious to repair. I spend probably 3 hrs, with magnify glasses exploring/repairing this. It's not for the faint of heart. The fine wire had broke. But finding the break at the comp box or in the probe at the switch, resulted in me taking the whole thing apart. It was quite an education. But It got me thinking.

It's a very simple concept. But the implementation is extremely difficult. I've got a mix of Tek probes with readout pins. I also have other Tek and non-Tek probes, without the pin . I started looking into "spoofing" the readout ring on the scope to make the adjustment for the proper readout value, particularly with non-readout probes. There are a number of solutions out there on the internet, involving the resistor placement. But none we're what I considered "elegant". So, I've gone to work to create that. The results is TekRing (TekRing.net) . It's a 3D printed "washer" that slips on the BNC before the probe is installed. It has a SMD resistor embedded with contacts out to the ground, providing "feedback" to the readout ring,. This provides the correct resistance to the scope so your V/div properly reflect the correct values.

I'm now using these with my 2465b scope. They work well. They are however finicky and time consuming to build. Axial resistors (1/4w and 1/8w) are too fat to be placed inside the washer, and must hang outside, which I find objectionable. (if I could find 1/16w axial they may fit?) Hence the SMD parts. Then getting the contact soldered and embedded is quite a procedure. But, it's working. I've got a few in my amateur radio friends hands now and they like them. I stuck together a little web site about the part.

Note, this only "fixes" the readout value of a probe not "telling" the scope is value. It doesn't make a low mhz probe function any better. But at least you don't have to do the 10x math in you head.


David Slipper
 

Excellent - just what I need :-)   What is the URL for your site ??

Can I suggest that you put the design up on "Thingiverse" as I am sure that many people would be interested.

Regards,
Dave

On 29/10/2020 16:35, Brent W8XG wrote:
I realize this is an old thread, but I've just repaired a p6129b probe. It has a readout pin, but the scope was not seeing it in 10x when the switch was in that mode. (it has the 1x /10x switch). In 1x, the resistor is simply switched out. So, the ring "floats" putting the scope in 1x mode. With the switch is in 10x the little 1/16watt axial resistor (11k - it's in the compensator box) is switched in, resulting in the scope switching it's V/Div values by 10. Mine had quit. I took it apart. There is a very, very fine wire running from the readout pin, thru the resistor, thru the switch, then to the BNC ground. It's tedious to repair. I spend probably 3 hrs, with magnify glasses exploring/repairing this. It's not for the faint of heart. The fine wire had broke. But finding the break at the comp box or in the probe at the switch, resulted in me taking the whole thing apart. It was quite an education. But It got me thinking.

It's a very simple concept. But the implementation is extremely difficult. I've got a mix of Tek probes with readout pins. I also have other Tek and non-Tek probes, without the pin . I started looking into "spoofing" the readout ring on the scope to make the adjustment for the proper readout value, particularly with non-readout probes. There are a number of solutions out there on the internet, involving the resistor placement. But none we're what I considered "elegant". So, I've gone to work to create that. The results is TekRing (TekRing.net) . It's a 3D printed "washer" that slips on the BNC before the probe is installed. It has a SMD resistor embedded with contacts out to the ground, providing "feedback" to the readout ring,. This provides the correct resistance to the scope so your V/div properly reflect the correct values.

I'm now using these with my 2465b scope. They work well. They are however finicky and time consuming to build. Axial resistors (1/4w and 1/8w) are too fat to be placed inside the washer, and must hang outside, which I find objectionable. (if I could find 1/16w axial they may fit?) Hence the SMD parts. Then getting the contact soldered and embedded is quite a procedure. But, it's working. I've got a few in my amateur radio friends hands now and they like them. I stuck together a little web site about the part.

Note, this only "fixes" the readout value of a probe not "telling" the scope is value. It doesn't make a low mhz probe function any better. But at least you don't have to do the 10x math in you head.




.


Brent W8XG
 

Hi David,

Thanks, it's www.tekring.net The project started out quite simple. But it turned into a very deep black hole. The 3D print creates the "washer" itself (that part is simple). However, embedding the SMD and contacts is another matter. It's quite detailed and has taken me a lot of fiddling and learning of how assembly this (under a micro-scope). I really doubt many will attempt this, unless they really like working with SMD's. I've probable destroyed 30-40 printed washers and a while roll of SMD's learning a repeatable technique. it's still not a quick process, and the acceptable success rate is still in the low 20% range. Build and test it. Repeat test.


John Griessen
 

On 10/29/20 1:53 PM, Brent W8XG wrote:
it's www.tekring.net>
The 3D print creates the "washer" itself (that part is simple). However, embedding the SMD and contacts is another matter.
Have you considered capacitive discharge welding to attach the SMT resistor end to the contact ring?


Brent W8XG
 

Hi John,

The concept of the ring is to put it on or take it off, depending on the probe being used (1x or 10x). The scopes don't have a manual switch (like my modern cheap digital one does) to tell it you have a dumb 10x probe on. So this resistor ring is creating that switch function. You don't want to weld to the ring in a permanent fashion to the scope. I do have to solder very fine wires on to the SMD to create the contacts out each side. Capacitive welding of the wire to the SMD is an interesting idea however. I've never done that, but the circuit looks easy enough to work up. A little jig might help?? Thanks,