Good, Dvm: Fill & Download for Free

A scope shows you the wave form from a amp, buffer or any other devise. The function generator adds a signal square wave, sine wave and the scope shows what has happened in the circuit. Properly used it can show cutoff, flat-topping, strange output wave shaping. A good scope can see RF within a receiver and or a transmitter. Can detect AC component from unit. It can also be used for bias within a tube set.Any good diagnostic test bench should have one. Signal generator, function generator, oscilloscope, grid-dip oscillator, watt-meter and dummy load. Plus a good DVM, DMM. I also have a 1955 Simpson 260 VOM.

Repairing things is probably the hardest thing to do in electronics. It’s a tough thing to have as your first objective. I’ve known a few people who are really good at electronics design, assembly, and theory, but couldn’t fix anything they didn’t design themselves.You will need to start by learning a lot of theory, so you can identify how a thing is supposed to work, and to break things down into blocks of functionality. You;ll also need to learn a lot of practical stuff, like how to identify components, and to understand what parts can be replaced by equivalent alternatives. You’ll need to learn how to use test and measurement gear, and therefore you’ll need access to some of that. A good DVM is de rigueur, a scope is virtually essential, and a decent bench power supply should be on the list as well. Learning how to solder and desolder, and use of basic hand tools will also be necessary.The theory part of your learning almost certainly needs to be accompanied by some lab work. For that, you’ll need to have the above mentioned equipment, as well as some other stuff, like signal generator(s), and probably multiple DVMs. You’ll need access to a wide array of electronics components and the means to assemble them into circuits that you can test and measure.If all of this adds up to something that sounds insurmountable, consider that there is a reason people learn this stuff by going to school. It’s pretty technical stuff, and fairly esoteric.You can probably go a little way in the field by simply learning a bit about basic wiring and assembly. Many faults are from physical damage, and wear and tear. Replacing broken parts can be learned a bit like learning how to repair household things; disassemble, inspect, identify fault, replace or repair the faulty part.I will leave you with one important step that most people seem to overlook: the separation of diagnosis and repair. Many people want to jump right to the repair part without actually doing any kind of diagnosis. Usually, the diagnosis is the difficult part, and the repair is relatively simple.Oh, and one more thing. There is danger involved. Don’t f**k with stuff that plugs into an AC power outlet if you don’t know that it is de-energized. That doesn’t mean switched off or even unplugged. Capacitors can and do hold enough charge to hurt you, even after the AC power source is removed. This is important. Always be safe.

There is no such thing as a ‘perfect’ op-amp. Due to manufacturing tolerances, there will always be a very slight variation of internal components in any integrated circuit. Where the circuitry is purely digital, these internal variations in component tolerance won’t really amount to anything. In digital circuits, a transistor is usually on or off.With analogue electronics, these very small differences can amount to significant errors when you are talking about circuits operating with gains of the order of 100s or 1000s.So…offset null.Assume you have a very simple op-amp circuit with no gain setting resistors. That is to say, you have the full open loop gain of the op-amp available. You short both the inverting input and the non-inverting input to ground. Both inputs have the same gain, and the same zero level DC signal, but when you look at the output on a good DVM or oscilloscope, you actually measure perhaps 100mV on the output.This is your offset. Caused by those slight tolerances in the individual components within the op-amp.The offset null pin on the 741 is intended to remove this offset for DC (steady state) signals. You can happily apply offset to a 741 that is operating on AC signals, but as AC is usually capacitor coupled at some point, this will generally remove any offset anyway.You would normally connect a potentiometer between two resistors connected to +VCC and -VCC and the wiper of the potentiometer generates a small voltage which is used to ‘null’ the output of the op-amp, thus removing any DC offset.It is very rare you will need much more than a volt of offset in either direction, so you wouldn’t put your null pot directly across the supply rails. I would normally use a 47k pot with each end of the track taken to +/- VCC with a 220k resistor.Like I say, for AC circuits the offset null pin is rarely used and simply left unconnected, but where you would definitely require the offset compensation is for analogue computing (integrators, differentiators, summers or subtractors, etc.) or for circuits like servomechanisms where any offset in your op amp can cause drift or other errors.