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Before you use the 'scope to check for supply line ripple, I would check the DC votlage of all the suppl lines using a multimeter. I asusme you have a digital multimeter rather than an analogue one, but I have no idea which one you hve and whether it has automatic or manual range selection. But the procedure is muc hte same in all cases. If it's an autoranging meter, switch it to the DC votlage (DCV) setting. If it's a manual range meter, switch it to a DC voltage range highr than the rail you awnat ot check, but not too high. Most meters have ranges 2V, 20V, 200V. The 20V ranges is the one you want for most computer PSU voltage tests. Connct the black lead of the meter to the computer 0V (logic ground) rail. In most DEC machbines this is connected to the metal casing. Touch the red probe onto the power rail you want to test with the machine turned on. Finding the power rails is the major problem, actually. You might use the pwoer pins of an IC on one of the boards. Or a pin on the connector between the power suypply and the backplane. Read the votlage on the meter :-). Now for 'scopes. I don;t know your 'scope (I prefer Tektronix...), but all 'scopes have simialr features. I would try to get the manual for the 'scope you have, it may well be on the Agilent website (they are putting up scans of a lot of their older instrument manuals). However, most test instument manuals assume you already know the basic principles of using such an instrument amd just explain the features of that particular one. The older non-digital CRT-based 'scope is a fairly simple instrument, and modern digital 'scopes have generally beed designed to work in much the same wayy for the user. The basics are : The electron beam in the CRT makes a bright dot on the screen. There are obvious controls for controlling the brightness and shapness (focus and astigmatism) of the spot. The input signal moves the spot vertically. There will be an intenral amplifier which will have a gain control calrated in 'volts per cm' or something similar (sometimes 'volters per division where a 'division' is one the squares on the graticule on the front of the CRT). If you wet that to 2V/cm and the spot moves by 2.4cm high on the screen, then that means the input is 4.8V Horizotnally, the spot is moved by a 'ramp' voltage from an internal timebase circuit. It moves from left to right at a constant speed and then quickly flies back to the left and repeats. The speed is controlled by a control calibrated in 'ms/cm' or something similar. Thus the 'scope ploits and displays a graph of the input voltage against time. You can m,easure the time between parts of the waveform (say time between peaks) or the votlage between parts of the waveform There are 2 other fauters that need mentioning. The first is the tirgger sicut. The purpose of that is to make the timebase wait for a particular input voltage (and the right direction of change) of the input signal. The idea is that assumign the input signal is repetitive, the timebase will start on a corresponding point of the wavefor each time, so you will get a steady trace on the screen that you can easily view ans makemeasueemtns from (as an aside, the purpose of storage 'scopes, whether analoge or digital, is to be able to hadnle non-repetitive waveforms. You effectively record the waveform for one sweep of the timebace and display it for evermore). The oterh feature is 'AC coupling' Most 'scopes have a swixch in thge vertical section for htis. It has the same effect as connecting a capacitor in series iwth the input signal (in fact in most caes that's what it really does). It removees the steady DC component of the inptu signal and only lets the AC part through to the amplifier. For example, suppose you have 100V supply rail with 0.1V ripple on it, and you want to look at the ripple. To display that supply rail, you probably have to set the Y amplifier to 50V/cm, which means the ripples is 0.02mm high. You can't see that. If you switch to AC coupling, the steady 100V is ignored, so you can turn up the gain of the Y amplifer, perhaps to 0.1V/cm at which point the ripple is easy to see. A word about probes. Most times you use a proper 'scope probe. This has a gorund lead which is actually conencted to mains earth throguh the 'scope so you can't connect it to just any point in the circuit. However, connecting it to the logic ground rail is fine (and what youshould do). Do not however assupe that the conenction through the mains earth is enough (and that you cna ignore the ground lead), it may be OK for low frequencies, but at high frequences the inducatance of that path through the mains earth wires is enough to mess up the display. Most 'scope probles sau '*10' or somethign similar on them. This means they attenuate the signal by a factor of 10. If you set the 'scope to 0.5V/cm when using such a probe the real sensitivity is 5V/cm. There are good reason ofr having this attenuation in the probe, mainly reducing the effectif ogf the capacitance of the cable to the 'scope on the circuit under test. Will that get you started? -tony