Re: Replacing cable on P6075A probe


Colin Herbert
 

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Daveolla
Sent: 17 November 2020 17:44
To: TekScopes@groups.io
Subject: Re: [TekScopes] Replacing cable on P6075A probe
Greeting, Also, take note of what the manual says about shortening
the cable and Connector Replacement" page 2 ( 6 of 11) of the P6075A
version from the links given earlier in this thread;
http://w140.com/tekwiki/wiki/P6075
It is also repeated (or vise versa) in the plain P6075 manual on page
5 at the same link.
It states;
"Substitution of non-standard parts is not advisable if the original
performance is to be restored. Even shortening the cable by more than
a few percent will have a noticeable effect on the transient response
of the probe. The resistive center conductor has been specifically
selected for critical dampening of reflections that would otherwise
exist."

And then is the "Conector Replacement" next with step 1 as "Remove
the snap- fit cover on the compensation box." They dont tell you how
to do that though. Perhaps the plastic has stiffened
somewhat suggesting you need a good pry from a screwdriver. Perhaps
a blade edge of knife gently if a finger nail wont budge it. It can
also be stuck and needs to be cracked loose. If you nick or dint then
you gotta fix that somehow........or I do. Leave no marks is the goal.
Im sure we have all seen somones attempt at opening stuff up, TVs,
phones, etc that looked like a jackhammer attacked it everywhere. Use
a screwdriver for what it was intended, prying open paint cans!!!
So why is it called a screwdriver and not a paintcanpryer? Sorry, but I can
be a bit funny about the misuse of tools - I hope you were joking, here.

On a side note, what is the difference in the plain P6075 and the A
version? I see the specs for the plain versions input impedance is
10meg within 0.4% and 0.5% for the A.
Dave
At 07:51 AM 11/17/2020, you wrote:
Not quite right to compare 250 to 10Meg and declare 200 to be
therefore ok. By that logic, zero ohms should be just fine, too.
Yet, Tek went to the trouble to use resistance wire. Clearly there's a
reason!

The purpose of the resistance wire is to damp out reflections due to
mismatch. There's a Goldilocks optimum for each length that balances
bandwidth against aberrations. If you deviate from that balance,
either parameter degrades.

That said, you're probably not going to notice any dramatic change.
But if you had before and after measurements, you'd see a difference.

Tom

Sent from my iThing, so please excuse the terseness and typos

On Nov 17, 2020, at 5:24, "Brent W8XG" <brent@pwg.net> wrote:

No, I did not do a YouTube video. But I've seen one out there. I
didn't have a replacement cable or other parts. I cut my cable off
at both ends as close as I could to the strain-relief parts, then
tested the cable. It tested good, so I knew I'd cut out somewhere
the break. I used the typical wire strippers to remove the
insulation. I was very slow and methodical. But I was surprised at
how fine that wire was. Then I had to clean out both strain
relief's, with a Dremel. Once cleaned out, I pried them open just a
little, to be able to slip the cable in and then crimp.

So my cable is now a little shorter. The 250 ohm's is likely
about right given the size of the wire, but I didn't measure it. So
my cable might be 200 ohm's now. But with the 9k resistor in there
to make it a 10x probe, I doubt it matters much.

I don't know what the grommet is for. Maybe it's to slip over the
cable and then crimp to become strain relief??

Regards,





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