Scoping the supply lines (was RE: new here)

Do you have documentation for the scope? The HP stuff is usually good about "first time user" guidance. Agilent (the test equipment spin-off from HP) has it online: Google hp1703a manual for the link (it's a weird dynamic link or I'd just include it here). I have two scopes of this line, I can't recall exactly which ones but I think the 1701 and 1702. It's a very good scope, but there are a lot of knobs on the front. :-) Fortunately most things require using only a few of them. You'll want to look at volts/div, which is the input sensitivity and controls the vertical aspect of the display; input coupling (AC/DC/GND), which either allows or removes the DC component of the input signal (or grounds out the input to the channel); time/div, which is the sweep speed and controls the horizontal aspect of the display; and triggering, which controls whether the sweep actually... sweeps! Set it to 'auto' for most purposes, but if you read nothing else from the manual, read about triggering. It gives you a lot of control over what you see on the screen. What I would recommend is using the scope to look at all the voltages from the power supply. Probably the easiest way to do this is to set the input coupling to AC and (with a 10:1 probe, which is what most scopes come with) set the input sensitivity to 0.1v/div, and set the time/div to maybe 10mS or so. This means that each vertical division on the screen represents one volt. If you see one or more volts of waveform with this setup, you have a problem. A ripple of 1v on a 15v line isn't great but isn't a deal-breaker; on a 5v line, it represents a 20% variance over time, which is bad. (Actually, you really don't want more than a token ripple on the 5v rail - even a half-volt is 10% and can really confuse the logic.) Ideally, you would see a flat line; if you switch the input coupling to DC, the trace should displace 1v/div (e.g. the 5v rail would displace five divisions from a no-input trace). To reiterate: with AC coupling, if you're looking at a pure DC input there will be a flat line at zero volts. I know it doesn't need to be said, but I'll say it anyway: be sure you've hooked the ground lead from the probe to a good voltage ground! On the stuff you're working with here, the chassis of the power supply is a ground reference. Cheers -- Ian