OT: Semi-functional scope?

Scopes are pretty simple beasts. Basically they work as follows: Part 1: 1) Hold the beam of to the side waiting for a "trigger." 2) When the trigger occurs send the beam to the right of the screen at a very well calibrated speed. 3) Go to 1) Note: There is a knob called "horizontal position" that biases the horizontal deflection circuit so that the beam starts at a particular point (left/right) on the screen. You may want to start with this in the mid-point position. Part 2: 1) Connect a signal amplifier to the vertical deflection circuit of the scope. 2) Adjust the gain of the amplifier such that a specific voltage results in a specific deflection of the beam vertically. NOTE: there is a knob called "vertical position" somewhere that biases the vertical input such that the beam sits on the scope at some point with zero input signal (ie grounded input). To start you should set this to the mid point. Both parts run simulataneously, so when you feed a repeating signal into the input, and trigger the scope at an even multiple of the input frequency, you see what appears to be a static display on the tube. Scope checkout then requires three steps: 1) Check out the triggering circuit. 2) Check out the vertical amplifiers. 3) Check out the calibration of the above. Some very simple scopes have only two trigger modes "Line", and "Ext". When set to "Line" they trigger every time the AC power crosses 0 or 60 times/second. On "Ext" they trigger whenever the signal connected to the external trigger input exceeds a particular threshold (usually settable, sometimes it is fixed at 0 volts). Once you have found the triggering section, set it to "Line". You should now see a horizontal beam. If you don't try moving the vertical position knob back and forth to see if you can make it appear. If you can, adjust the knob so that the beam crosses the middle of the screen. Hook up a square wave source (a kludged up 555 works well for this) to the trigger input. Set the trigger for "Ext" verify that you see the beam again. Now put the trigger back to "Line" and hook up your square wave source to the channel 1 input (or sometimes called Y input). You should now see two lines or perhaps some square waves all jumbled together. If you don't see them, but you do see a line when the square wave is disconnected, then set the gain (the knob marked "volts/division" to a higher number. Repeat the experiment. Now check to see if your triggering section has a setting for "channel 1" or "Internal". Set it there and the squarewaves should stop jittering and appear. At this point changing the "time base" knob will change how many cycles of wave you see and changing "volts/div" knob will change how big they appear on the screen. --Chuck At 06:58 PM 9/21/99 -0400, you wrote: