AC DC Voltage tests?

"Uriah"

...... Phil

There are many guidelines ... for example, the Vbe drop is always around 0.7 volts when a transistor is turned on. The Vce drop is always about half of the supply voltage in a linear amplifier.

The voltage drop across a resistor is current X resistance.

There are many instances when the drop across a capacitor is 0. And, there are many when this is not so.

I was just reading in Perozzo's book where He said that a Zener Diode should have a voltage drop equal to its ratings. So a 12volt Zener should have a 12 volt drop on it. This sounds simple enough. So I am going to check a few out to see if it follows.

Would a cap ever have 0VAC and 0VDC across it when measured with a scope?

And if I see .7Vbe on a transistor then I should get some kind of larger drop on Vce? , and if not that might point to something?

:> > Are there any basic guidelines for testing caps, transistors, :> > resistors,etc, in-circuit with power on? I know there are a lot of :> > variables but can you discover any clues from a meter or scope when :> > checking voltage across components without a schematic? I am working :> > on a monitor chassis and am just wondering. For example, with power :> > on using a DVM and checking caps should they ever read 0VDC? What :> > about diodes or resistors or transistors? In general. On transistors :> > should I always read some kind of drop between C&E. Or would 0V show :> > me anything. I hope there are some clues because I am running out of :> > options on this one. :>

:> There are many guidelines ... for example, the Vbe drop is always around 0.7 :> volts when a transistor is turned on. The Vce drop is always about half of :> the supply voltage in a linear amplifier. :>

:> The voltage drop across a resistor is current X resistance. :>

:> There are many instances when the drop across a capacitor is 0. And, there :> are many when this is not so. : :I was just reading in Perozzo's book where He said that a Zener Diode :should have a voltage drop :equal to its ratings. So a 12volt Zener should have a 12 volt drop on :it. This sounds simple enough. :So I am going to check a few out to see if it follows. : :Would a cap ever have 0VAC and 0VDC across it when measured with a :scope? : :And if I see .7Vbe on a transistor then I should get some kind of :larger drop on Vce? , and if not :that might point to something?

I am starting to get worried...

You appear to have little knowledge about components and how they work yet you are blundering around in a live computer monitor - you are bound to have a bad end.

Components in live circuits don't necessarily have volt drops or anything else. This depends upon circuit function. You have to know how the circuitry around the components functions in order to determine if what you see or measure is within expected parameters. Your zener diode might be operating as a peak clipper for a varying voltage so you won't be able to measure a steady state voltage across it. Unless you know how the circuit should operate in the first place otherwise you are just guessing.

This sounds very dangerous! Monitors contain very high voltages, 1000s of volts, and this can be stored in capacitors so you can get a shock even when it isn't plugged in.

If you want to learn about electronics start with something safer.

If you want to get a working monitor just buy a new one. You are unlikely to find the fault without the schematic, and even if you do, it will be difficult to get a replacement part.

It isn't worth risking your life over an old monitor!

Say "Hello" to Lindsay for me (same given name as you!) - knew her at NEC and a number of recent GSM sites