TEK2221A Scope Usage

[LoveChet]

Just got a oscilloscope (TEK2221A). Is this forum a proper place to ask about general use as in how not to kill it checking out my Fender Deluxe amp , etc etc

[LoveChet]

BTW how can I correct the topic name ?

[g1]

edit: thanks for fixing and moving, big_teee !

[big_teee]

Thread moved, and Title Changed.
Mod-T

[loudthud]

Inputs are protected to 400V peak with a 1X probe. Note that most Tek 10X probes also have a 400V peak limit. If you can find a 100X probe, that would have a higher Voltage limit, but you have to check the limits of each probe model. AFAIK Tek doesn't make a 1X-10X switchable probe.

A 10X or 100X probe requires an adjustment to compensate for the input capacitance of the oscilloscope. If you don't know how to do this, try looking on U-Tube, search for "Oscilloscope Probe Compensation".

Now that you own one, avoid the embarrassment and spell Tektronix correctly. I just had to add it to my spell check dictionary.

[Greg Robinson]

Also, depending on the model of oscilloscope, the division factor may or may not apply for DC voltages in AC coupled mode. Some oscilloscopes AC couple before the 1Meg input impedance, others after. This may be buried somewhere in the manual, or be completely absent. Easiest way to check is to set your scope for AC coupled mode and use a multimeter to check for DC resistance at the BNC input of the scope. If you measure OL or significantly higher than 1Meg then DC voltages are not divided in AC coupled mode. Ideally you should get a reading of ~1Meg, in which case the division factor applies to both AC and DC modes.

[loudthud]

First off, a link to the Operations Manual : https://w140.com/tekwiki/images/b/bc/070-8156-02.pdf

Google is pretty good at finding Tek manuals, if you have Tek probes, search for the manual(s).

The limits on input Voltage are on a graph on page A1. For the old scopes I have Repair Manuals for, the capacitor used for AC coupling is a .019uF 600V. To protect the input of the scope when using AC coupling, first set the input coupling switch to GND. Connect the probe to the circuit with DC, then move the coupling switch to the AC position. This protects the input from the nasty charging currents of the cap, the cap charges through a 1Meg resistor. Same when you disconnect the probe. Set the switch to GND, disconnect the probe and touch the tip to ground, then you can move the switch to DC.

Tek seems to always put the AC coupling cap at the input where the DC-GND-AC switch is. Having the cap downstream doesn't make any sense, it would be like having a cap feeding the grid of a tube.

[JP-Stereo]

One important thing to respect is the personnality of the ground of the Device Under Test...
All the Scope measurments are in reference to it's grounds.
Here an isolation transformer come handy, it may be applied to the DUT or to the Scope itself.

So if the Line and the Returns are ever inverted, no spark.
A lot of amp circuits also have mid rail ground that are a kind of floating so most scope can't take it for a ground reference to test a rail, since it's not at the same exact potential of the Scope's ground.

In some case, only a battery powered scope is insulated enough or a multimeter...

[Greg Robinson]

Here an isolation transformer come handy, it may be applied to the DUT or to the Scope itself.

You must NEVER float the scope. It is completely unsafe. If you can't think of a way to perform testing safely without defeating the protective earth of a mains powered scope, you're doing something VERY wrong. Only ever float the DUT, use an isolated (battery powered) scope, math function with two channels, or a differential probe. There are ALWAYS other options besides defeating scope ground, and they are ALL MUCH safer.