Snap-On Low Amps Probe (MT3000A440); What does it do?

[lschwarcz]

Hi Everyone,

I have a Snap-On MT3000A Counselor II 'scope. I has the Amp Probe but I also see online the "Low Amps Probe" (MT3000A440) and it's listed in the user manual as an optional accessory. But, I can't find any information about what it's for or how to use it.

Is this information hiding in plain sight in the manual and I'm just overlooking it? Is there some other documentation for it that I just haven't found? Any pointers or clues?

Thanks!
Larry.

 

[2ndGearRubber]

I know nothing of your specific scope: however a low amp probe is typically 20 or 60 amp peak, designed for things like motors, ignition coils, fuel pumps, injectors, etc.

I like them for intermittant shorts, identifying if it's a component overloading the circuit or an actual short.

 

[lschwarcz]

Hi Everyone,

I have a Snap-On MT3000A Counselor II 'scope. I has the Amp Probe but I also see online the "Low Amps Probe" (MT3000A440) and it's listed in the user manual as an optional accessory. But, I can't find any information about what it's for or how to use it.

Is this information hiding in plain sight in the manual and I'm just overlooking it? Is there some other documentation for it that I just haven't found? Any pointers or clues?

Thanks!
Larry.

I found a bit more information about this specific attachment. It's not mentioned in the user manual but I did find some info in the service manual. I also discovered that when you bought one it came with some supplemental pages you were instructed to put in the back of your user manual.

From the service manual:

GENERAL
The High Amp Probe is used for the Cranking Amp Bar Graph Screen and the Lab Scope Screen. The Low
Amp Probe is used to gather amp readings in the 20 amp (or less) range. These “low amps” readings are
displayed in the Lab Scope Screen. Both probes consist of an inductive probe and a printed circuit board in a
small metal case. The AUXILIARY connector from the Main Leadset is connected to the 16 pin connector on the
Amp Probe interface box.

A three pin lead identification system informs the tester that the Amps Probe is connected and how the signal
processing circuitry should be configured. The pins are grounded or pulled high to form a code identifying the
device that is connected.

THEORY OF OPERATION
HIGH AMP PROBE

The High Amp Probe provides an output of 1 volt for every 100 amps sensed by the probe. The circuitry on the
printed circuit board (in the Amplifier Box), provides the needed amplification, offset adjustment, and filtering for
the signal. The output from the High Amp Probe can be used on the Lab Scope Screen and the Cranking Amp
Bar Graph screen.

There are 4 connections to the Hall Effect chip. The red and black wires are for the positive and negative control
current (25 ma). The white and green wires are the signal outputs from the Hall Effect IC. This signal is
connected to an instrumentation amplifier composed of 3 operational amplifiers. The first 2 operational amplifiers
provide gain and allow an offset adjustment to null out the Hall Effect probe and operational amplifiers. The third
op amp changes the signal to a single ended signal, and is followed by a low pass filter to remove noise. The
output is connected to the Aux A line of the AUXILIARY lead of the main leadset. The AC coupled amplifier
connected to Aux B is not used for anything at this time.

For the High Amp Probe, the ID1 and ID2 lines are pulled high, and the ID3 line is connected to ground. This
signals the scope that the High Amp Probe is connected to the leadset.

LOW AMP PROBE
The circuitry on the printed circuit board of the Low Amp Probe provide the needed amplification, offset
adjustment, and filtering for the signal. The output from the Low Amp Probe can be used on the Lab Scope
Screen. The Low Amp Probe outputs to the AUXINA input only.

The Amp Probe has 3 voltage regulators, + 8 and - 8 volts for the circuit power. Another is used as a constant
current source for the Hall Effect chip in the probe.

There are 4 connections to the Hall Effect chip. The red and black wires are for the positive and negative control
current (25 ma). The white and green wires are the signal outputs from the Hall Effect IC. This signal is
connected to an instrumentation amplifier composed of two operational amplifiers. These operational amplifiers
provide gain and allow an offset adjustment to null out the Hall Effect probe and operational amplifiers. The
output is connected to the Aux A line of the AUXILIARY lead of the main leadset.

For the Low Amp Probe the ID2 and ID3 lines are connected to ground, and the ID1 line is pulled high. This
signals the scope that the Low Amp Probe is connected to the leadset.

I found one used on eBay that includes the supplemental instructions. When I get it I'll scan and post them.

Thanks!
Larry.

 

[Schurkey]

The low-amps probe is wonderfully handy, although I didn't realize it was only good to 20 amps. I don't use mine much since getting a different low-amps probe usable with multimeters and 'scopes. The low-amps probe is used for looking at fuel pump motors, HVAC blower fans, electric radio antenna motors, and so forth. You can check the amperage draw of each individual bar of the motor armature; and calculate motor RPM. Fuel pump diagnosis is especially useful, since labor to change the pump/motor is often very high.

For the record, the MT3000A is a real upgrade over the previous MT3000; the "A" revision includes additional protection circuitry, and has the capacity to measure Lambda when used with the matching exhaust-gas analyzer (if the "special" O2 sensors for the exhaust analyzer are still available.)

I had a '3000A until a garage fire destroyed it. Replaced with a '3000.

Either one--3000 or 3000A--is a fabulous automotive oscilloscope, but getting old and potentially unreliable now.

 

[lschwarcz]

Hi Everyone,

I have a Snap-On MT3000A Counselor II 'scope. I has the Amp Probe but I also see online the "Low Amps Probe" (MT3000A440) and it's listed in the user manual as an optional accessory. But, I can't find any information about what it's for or how to use it.

Is this information hiding in plain sight in the manual and I'm just overlooking it? Is there some other documentation for it that I just haven't found? Any pointers or clues?

Thanks!
Larry.

I added the Low Amps Probe manual to my post with the other Counselor II manuals. You can find it here:

Snap-On Counselor II MT3000A Service/Repair manual. FOUND THEM!

Hi Everyone, I just bought a used Snap-On Counselor II MT3000A. It came with the user manual but I'm hoping someone out there has a service/repair manual for it too. Being so old it's bound to need some work eventually! I'm also missing two of the cables; The Main Lead Assembly (MT3000A200)...

www.garagejournal.com

Larry.

 

[Schurkey]

^^^ THANK YOU for posting those manuals!


Oh, yeah.

The Counselor II (MT3000/3000A) was also sold as a "Sun" branded product. I don't remember the model number. It used a different housing and keypad. (Different "form factor".) I've only seen photos of them, but so far as I can tell none of the function changed, but they look completely different.