I'm new here. I've spent much time reading through posts and realized I had not seen any posts on basic or safe use of test equipment. What prompted this post was one post I read where a forum member had ordered an o'scope and was asking how to use it to view signals in his amp when it arrived. With the safety culture my recent employers are developing this set off an alarm with me.
Being relatively new to guitar amps I'm not able to contribute much to the technical discussions. However I've worked with electronics since the '80s so do feel qualified to contribute in this way.
While many, if not most, members here are well experienced in the use of test equipment I'm sure there are some who may be new to it-this is an opportunity for the former to share their experience and knowledge with the latter.
If I pass on something dangerous or incorrect please correct me.
One hand rule: only have one hand near/in an amp that is powered up. If you have the other resting on the amp chassis you are providing a path for current to flow through your chest. Put your other hand in your pocket or behind your back.
First up: oscilloscopes. Before using one on an amp, become familiar with your particular scope. There are MANY scopes available and all have their own way of making adjustments. I'm not going to cover the HOW, just the WHAT you should know.
You should know how to adjust it to properly look at a live signal by correctly triggering it and adjusting the amplitude and offset controls at a minimum. A separate signal generator is useful for this as well as being useful for amp troubleshooting.
Know the max voltage rating of the scope and never exceed it. If you need to look at a higher voltage signal use a 10x or 100x probe. When using a 10x or 100x probe many scopes have a setting you can change so the voltages it displays are corrected, others do not so you must do the calculation in your head. I.e. if the scope does not have a setting for a 10x probe but you are using a 10x probe, and it is showing a 5vpp sine wave the wave is actually 50vpp. Know your equipment.
Be able to calibrate the probe. Many scopes have a signal generator that can be used for this purpose.
A scope needs two connections to show an accurate waveform, a reference (typically chassis common or ground) and the signal you wish to view. Know if the scope's grounds for the channels are internally connected. In my experience most are. This is useful because only one ground reference is needed for all channels.
The following is how I use my scope:
My scope was purchased from Amazon for about $200 a couple of months ago. While I have used scopes far more capable (and expensive) this one is more than adequate for amp work.
This scope included a lead with a BNC on one end and two alligator clips on the other. All grounds on my scope are connected internally. I connect this lead to the Sig Gen Out and black clip to the amp chassis, now I have my reference.
The probes I have are equipped with removable ground clip. If this clip were to inadvertently slip and contact live circuitry it could be BAD. Using this clip also severely limits where I can look at signals because it is very short. I remove it. The probe tip has two contact surfaces, a center pin that needs to be put on the point under test, and a ring that is connected to scope ground. Never use a naked probe like this, if you slip you can short something to ground through the scope (remember I connected scope ground to amp chassis earlier). My probe came with an insulator that fits over the tip, covering the ground while allowing the center pin to protrude, and a sleeve with a spring loaded clip. I use either of these as needed.
When I first started, and often still do, is power down the amp-make connections-turn on amp to view waveform. Repeat for each measurement. When I am capturing waveforms I do this.
Topic: Test Equipment-Using it SAFELY and Effectively (Read 4022 times)