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Schematic for Tek P6137 scope probe?

J

Joerg

Jan 1, 1970
0
Is there a schematic for that probe somewhere on the web? Or does
someone know what would be a good replacement for the main calibration
variable cap it there? It's the red plastic one, SMT, square.
 
P

Phil Hobbs

Jan 1, 1970
0
Joerg said:
Is there a schematic for that probe somewhere on the web? Or does
someone know what would be a good replacement for the main calibration
variable cap it there? It's the red plastic one, SMT, square.

I'd measure the capacitance on the scope end, add 10 pF for the scope,
and then divide by 9 to match the voltage divider. That of course
neglects other capacitance in the circuit, but for a trimmer it ought to
be reasonably close.

Cheers,

Phil Hobbs
 
J

Joerg

Jan 1, 1970
0
Phil said:
I'd measure the capacitance on the scope end, add 10 pF for the scope,
and then divide by 9 to match the voltage divider. That of course
neglects other capacitance in the circuit, but for a trimmer it ought to
be reasonably close.

Yes, I'll probe it out if there is no schematic. But these things are
way more complicated. IIRC there were several other trim caps and three
potmeters or so in there. Plus some fixed value SMT components. The
gold-plated BNC as well as the tip cable are clicked into slip ring
holders. Quite impressive, actually.

At least I was able to finish the measurement by wedging a piece of
toothpick in there. Not so with the baseband analyzer. It had been
literally destroyed in shipping. Wanted to measure phase noise on VCSELs
but I guess that has to wait now :-(
 
M

Michael A. Terrell

Jan 1, 1970
0
Joerg said:
Yes, I'll probe it out if there is no schematic. But these things are
way more complicated. IIRC there were several other trim caps and three
potmeters or so in there. Plus some fixed value SMT components. The
gold-plated BNC as well as the tip cable are clicked into slip ring
holders. Quite impressive, actually.

At least I was able to finish the measurement by wedging a piece of
toothpick in there. Not so with the baseband analyzer. It had been
literally destroyed in shipping. Wanted to measure phase noise on VCSELs
but I guess that has to wait now :-(


I thought that the color of the variable capacitor's body told you
its range? I've seen charts that told which color was what range, but
its been a few years.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
J

Joerg

Jan 1, 1970
0
Michael said:
I thought that the color of the variable capacitor's body told you
its range? I've seen charts that told which color was what range, but
its been a few years.

No idea. I am used to ceramic trim caps where the range is printed onto
the base. But on my designs I never use any of that, it's all electronic
auto-calibration so I haven't kept up with the fashion trends ;-)
 
T

Tom Bruhns

Jan 1, 1970
0
Is there a schematic for that probe somewhere on the web? Or does
someone know what would be a good replacement for the main calibration
variable cap it there? It's the red plastic one, SMT, square.


Might it be one of the muRata TZV4 series? Have a look at DigiKey
490-1980-1 and 490-1981-1; slightly different lead configurations of
the same thing. 20pF max, 4.5pF min, N750 tempco.
 
J

Joerg

Jan 1, 1970
0
Tom said:
Might it be one of the muRata TZV4 series? Have a look at DigiKey
490-1980-1 and 490-1981-1; slightly different lead configurations of
the same thing. 20pF max, 4.5pF min, N750 tempco.

Thanks, Tom. Those look a bit larger but could possibly fit. Next time I
am at that client I'll unsolder one and measure it.

The 2nd P/N datasheet link resulted in an invalid part number. But that
isn't anything new at Digikey. After they botched the search engine last
time it hasn't been the same. There are times where just waiting a few
hours fixes a link, then the next day it's broken again.
 
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