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Tek p5205 HV differential probe teardown. BTW, what are the red and brown wires?

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128er:

--- Quote from: onlooker on November 17, 2014, 03:40:15 am --- 2). The P5205 was speced to use +/-15.0V power. Will a +/-10.5V supply be adequate?

--- End quote ---

Can't remember which parts of the circuit use the +/- 15V. But IIRC the +/- 15V input is directly followed by two adjustable linear regulator, one for +5V and the other for -5V. And they power most of the probe circuit. Have to look in one of my probes.


--- Quote from: David Hess on November 17, 2014, 03:53:19 am ---Was the differential probe terminated into 50 ohms on the oscilloscope?

--- End quote ---

Don't know if the OWON is capable of 50 Ohm termination. But the probes are specified for 1 MOhm input impedance.



But it is nice to see that the thread is not dead. I have worked a little bit on my Tekprobe PSU at the last weekend.

I like Onlookers idea. It is more like a stand alone solution, instead of my brick like Tektronix 1103 clone  ;D

A few pictures of my PSU . . .

onlooker:

--- Quote ---The frequency of the ringing may yield a clue about the cause but I cannot see it accurately on your image.  Is it 130 MHz?
--- End quote ---

Yes, that should be about right.


--- Quote ---Was the differential probe terminated into 50 ohms on the oscilloscope?
--- End quote ---

MarkL had already quoted the manual earlier: The scope end must have an impedance > 50kR. Or as 128er mentioned, 1MR should be fine.

128er, Your 1103 clone looked quite authentic  and nice.


--- Quote ---Can't remember which parts of the circuit use the +/- 15V. But IIRC the +/- 15V input is directly followed by two adjustable linear regulator, one for +5V and the other for -5V. And they power most of the probe circuit. Have to look in one of my probes.
--- End quote ---

The output is speced to be +/-2.6V.  So, in theory, it is possible that a +/-5V supply is all needed, though a few chips on the PCB can work up to +/-15V. In any case, it should be an interesting item to followup on. If true, the requirement for the PS is further reduced.

David Hess:


--- Quote from: onlooker on November 18, 2014, 01:24:14 am ---
--- Quote ---Was the differential probe terminated into 50 ohms on the oscilloscope?
--- End quote ---

MarkL had already quoted the manual earlier: The scope end must have an impedance > 50kR. Or as 128er mentioned, 1MR should be fine.
--- End quote ---

I am thinking that the original cable had a compensation box on the end and was made from wire similar to x10 probe cable with a resistive center conductor to dampen reflections.  If that is the case, then modifying the new cable to work into a 50 ohm termination may be necessary to get full 100 MHz performance.

The 130 MHz ringing may be from the reflections along the length of the new cable and not anything to do with the probe end.

onlooker:
I would quote MarkL again about the "compensation box" of P5205 that connects to the scope:

--- Quote ---there's no compensation in it.  The coax goes right into the scope.
--- End quote ---

Also, my P5205 had about 5" coax left. The core was made of multi strand silver(?) plated copper wire like RG400.

Then, the manual says: "Output Type: Single-ended  Source Impedance of 50 ohms drives 1 M ohm oscilloscope input". That is, yes, the scope end will reflect, but the scope would never see it since the P5205 end has a matching impedance and will not reflect back the reflection. This is what was meant by "single-ended".

The square wave picture I posted earlier also showed that the output of p5205 followed the input "closely", including the ringing. That is, the ringing should be from the input of P5205. My input cables are about 20cm in length that are shorter than the original cables which are 30cm. I should expect less ringing? 

The problem is that the manual did not spec the ringing. Maybe they should spec it  in some way since the manual did have pictures showing extra ringing as an expected result of using P5205 and adviced to twist the input cable pair.

MarkL:

--- Quote from: onlooker on November 18, 2014, 12:07:13 pm ---I would quote MarkL again about the "compensation box" of P5205 that connects to the scope:

--- Quote ---there's no compensation in it.  The coax goes right into the scope.
--- End quote ---

Also, my P5205 had about 5" coax left. The core was made of multi strand silver(?) plated copper wire like RG400.

--- End quote ---
All the clues you point out correctly conclude it's 50ohm coax and not special resistive coax.

Plus, I'll also add that the 5205 can be used with the 1103 power supply, which you extend to the scope using 50ohm coax.

And to put the question to a final rest, I took the cover off mine and measured 0.1ohm from the BNC center pin to the cable termination solder joint in the 5205 main box.


In one measurement, you're showing ringing on both the input and output.  If you disconnect the 5205 from the dual banana adapter, do you still see ringing on the input coax?

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