is it safe to short op-amp inputs?

[SleeplessDad]

Sorry in advance for the stupid question but I am carry out a repair on an expensive PCB(about 5K)I can't afford to fry it.

There is a wandering analog signal. There are several op-amps in the amplification circuit.

Am I safe to short the input pins on an op-amp? I was thinking that I could work backwards shorting the different stages until I found where the drift was.

 

[Nigel Goodwin]

It shouldn't do any damage, but shorting out inputs probably isn't the best way to do this - bear in mind inverting opamps are virtual earth mixers, and you would need a really low impedance short to mute it. Far better to trace through with a scope.

 

[audioguru]

An opamp has a DC and low frequency voltage gain of about 200,000. Most opamps have an input offset voltage of up to 6mV. So if you short the inputs of an opamp together then you bypass the negative feedback and the gain of 200,000 times the offset voltage of a few mV will cause the output of the opamp to go to one supply voltage.

 

[kchriste]

Am I safe to short the input pins on an op-amp?

In general, yes. Whether you can do this depends on several things.
What is driving the input? Can the circuit driving the input sustain a "short"?
What is the op-amp driving? ie: If, for example, the op-amp is part of the power supply circuit, will shorting the inputs cause the supply voltage to rise too high and damage other circuitry?
Usually when trying to inject DC offset into a circuit like that I will use a resistor in series to limit the current for safety reasons. A dead short is risky on a $5K PCB if you aren't 100% certain of what you are doing.