Agilent/Keysight N2893A Current Probe (Teardown and Repair)

[HighVoltage]

I just obtained another broken Agilent current probe with a cut wire and repaired it.
This one is the Agilent N2893A
- 15A Max current
- 100 MHz bandwidth

The repair was a success and the probe works now perfectly with my MSO7000B series scope.
The repair was easy and straight forward, so I share with you the teardown pictures and repair procedure.

This probe does not have a "zero" wheel, instead it is calibrated by the scope's software with the push of a button for "Demag & Calibrate".

[HighVoltage]

More pictures of the teardown and repair

[HighVoltage]

Last set of pictures

[lukier]

Very nice. I'm also looking for a current probe, but these things, even decades old (I guess) Tek probes hold their prices (except maybe AC only ones), beyond my wallet capability

I've noticed fair amount of probes with their cable cut on eBay, or sometimes each part listed separately. I suspect this might be intentional, something required by the accounting laws to dispose equipment and write it off the books - horrible practice!

[dom0]

Now I'm curious what they need the 13600 (OTA) and 675 (power OP) for... any schematics available?

[HighVoltage]

I've noticed fair amount of probes with their cable cut on eBay, or sometimes each part listed separately. I suspect this might be intentional, something required by the accounting laws to dispose equipment and write it off the books - horrible practice!

You are probably right.
I was also a little scared that someone might have deliberately killed something inside.
It really is a horrible way of getting new equipment for some companies, it seems.

[HighVoltage]

Now I'm curious what they need the 13600 (OTA) and 675 (power OP) for... any schematics available?

No, unfortunately there is only a "user guide" and nothing else, not even a calibration guide.
Maybe someone here on eevblog has any schematics?

Mechanically it is built very well and can be disassembled easily with simple tools.
So, it seems it was built for possible repairs.
But must likely for internal Agilent repair only.

[tesla500]

Now I'm curious what they need the 13600 (OTA) and 675 (power OP) for... any schematics available?

The power amp is used as part of the DC bias correction for the current transformer, allowing it to measure DC. I repaired the Tek version of of these probes awhile back, I believe they use the same Japanese made Hall/CT components as the Agilent ones. There's an overview of their operation at 4:55 in the first video below, and a look at the 1979 version of these probes/amps in the second video.

Tektronix TCPA300 current probe amplifier debugging


Tektronix TCPA300 debugging 2 and a look at an AM503 probe amp


AM503 service manual with schematics

[HighVoltage]

The power amp is used as part of the DC bias correction for the current transformer, allowing it to measure DC. I repaired the Tek version of of these probes awhile back, I believe they use the same Japanese made Hall/CT components as the Agilent ones. There's an overview of their operation at 4:55 in the first video below, and a look at the 1979 version of these probes/amps in the second video.

Thanks for the links to these really interesting videos and service guide.
I wish they would still make service guides like in those days.

Tomorrow I will do some more test's in the mA range, to see how accurate the Agilent probe is in the lower current ranges

[I4E]

Very Interesting!

Joy

[HighVoltage]

Ok, now the other side of the scale:
Here is a current measurement of a signal current of around 30 mA with a 750 us pulse duration.
It seems the Agilent N2893A is well capable of measuring this.
The limit of the probe / scope is 20mA / div.

[Mechatrommer]

i think you can reuse the cable end black holder. carefully slide out the damaged cord, poke with tweezer etc if necessary, slide in the other undamaged remaining cord and soldered to the probe. appearance back to original with only few cm short of the original cord.

[HighVoltage]

Hello Mechatrommer
That is exactly what I did.
The last pictures show the repair and the probe functioning.

I just tested the N2893A on my Agilent DSO-X 3034A
And it also works very well.
The probe calibrates itself via software and is really stable at this 1.0 MHz 13 mA RMS signal
I took a signal from a Agilent 33522B signal generator and shorted the output.

[HighVoltage]

Can you elaborate why they will do this? Seems reasonable, but not knowing why?

Some companies have the policy to only replace equipment that can not be repaired and then some genius just kills equipment.
I have seen it a few times now. I just bought a "dead" scope and all it had was a "removed" cable inside. Probably the same reason.

BTW, the current probe works still like a charm after a couple month.

 

[lukier]

Can you elaborate why they will do this? Seems reasonable, but not knowing why?

Something along these lines:

https://www.eevblog.com/forum/testgear/abused-test-equipment/
https://www.eevblog.com/forum/chat/i-died-a-little-inside-today/

[lukier]

So why not donating them or internally auction them? Also writes off things, without ruining them. Whoever made this rule is a BITCH.

Usually a piece of equipment depreciates 20% per year (assuming use 5 years before decommissioning), so at the last year, it worths 1/5 the list price.

Assuming a company pays 30% income tax, that makes it to pay 6% the list price if they auctioned it, instead of destroyed it. I'm pretty sure employees will be happy to own it for 6% the new price.

I completely agree. Unfortunately, people don't see destroying/dumping equipment the same way they see throwing away food or burning books. 

Also, various laws related to his were put in place I suppose, because buying used equipment for 6% of the price or getting it from the dumpster is bad for the economy, doesn't generate as much GDP as buying new stuff all the time.

[I4E]

 I guess it depends  on what kind of company you run.  If for some reason we got something like that  and couldn't sell it to another deal for parts we could atleast write it off as a loss I believe.   However having said that I'd never buy something in really rough condition .

 I know someone who actually went to the dumpster and dug out the unit the company tossed . It was  a unit that was easily worth 10K used. 
 
Have a good day everyone!

Joy

[radhaz]

Does that board say HIOKI on it?

[HighVoltage]

Does that board say HIOKI on it?

Yes, it does, see enclosed picture.
Is that the manufacturer or designer of the PCB?
You think this was not designed by Agilent?

[Someone]

Does that board say HIOKI on it?

Yes, it does, see enclosed picture.
Is that the manufacturer or designer of the PCB?
You think this was not designed by Agilent?

Many probes are rebadged, I only know of two manufacturers of those high performance current probes: Hioki (rebranded by HP/Agilent/Keysight and Lecroy) and Tek.

[r0d3z1]

R&S should be the only one big that design its own current probe

[HighVoltage]

R&S should be the only one big that design its own current probe

Which one?

All R&S current probes that I have seen at trade shows are Hioki type, looking exactly like Keysight probes.
Like in this attachment.
They are probably a "little" more expensive than other brands of the same type.

[r0d3z1]

Which one?

You are right, they looks like HIOKI.

[HighVoltage]

Yokogawa also has really nice current probes but they are also only a rebranded Hioki current probe, like this one.

I just bought a broken Yokogawa probe and fixed it to like new condition.

[PartialDischarge]

Yokogawa also has really nice current probes but they are also only a rebranded Hioki current probe, like this one.

I just bought a broken Yokogawa probe and fixed it to like new condition.

What do you measure with this probes, dc, sinusoidal or pulsed currents?

Also it did strike me that this models have a fixed scale, I still prefer the old tektronix am503 amplifiers where v/a scale is selectable for both the a6303 and a6302 probes