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Basic Troubleshooting - A Rationale
One of the most tense and frustrating moments in the adventures of a Do-It-Yourselfer is when the
project we have finished fails to "start right up the first time".
Fear not, this happens to everyone, even veterans with years of construction experience.
There are a few general, logical techniques to troubleshooting that can make the process a lot less
painful and actually quite a rewarding lesson. Remember, we don't learn from doing something right,
we learn from our mistakes. So forget the panic, take a deep breath, and get analytical for a mo-
ment…
Equipment
While a really hot shot tech might be able to diagnose a few problems based entirely on his past ex-
perience with a particular circuit, one really needs a minimal collection of test gear to sort out a prob-
lem. Most important (and most likely to show the location of the typical problem ) is the Volt-Ohm me-
ter, whether an analog meter or a digital voltmeter (a.k.a. DVM or DMM). Along with this a few clip
leads can be a tremendous help in hooking up meters, substitute parts, etc. For real "tough dogs"
and new designs an oscilloscope is almost mandatory, but we will deal here with the more straight
forward kinds of problems that are usually encountered when one completes an electronics kit.
An Example
Let's create a scenario to help us understand the troubleshooting process. You've been playing your
preamp for a couple of hours, and suddenly you started hearing a noise in one channel of your sys-
tem. It's making you crazy, and you're wondering how you ever talked yourself into the idea that you
could build your own gear.
Rule number ONE
Break the system into its component parts
I cannot emphasize this enough. The first step is to determine where in the system and/or where in
the component the problem lies. This is done by the process of elimination.
So let's slow down and get logical. Start by eliminating the parts that we know aren't broken. First we
know the problem is only in one channel. So let's not bother with the other channel, in fact if we can
turn the amp off on the channel that's OK, let's do so.
Now let's disconnect the preamp from the amp on the noisy side. Shut the amp and preamp off and
disconnect the interconnect between them. What we want to do now is to short the input of the amp.
You can do this with a shorting plug, which is just an RCA plug that has the center pin connected to
the outer shell, or you can just use a clip lead to short the center conductor of the RCA jack in the
amp to the ground tab on the RCA jack. Turn on the amp and see if you hear the noise.
For grins let's say you don't hear the noise. OK, now you know that the problem is not in the amp. So
it must be in the preamp or the source component ahead of the preamp ( i.e. your CD player, DAC, or
phono setup). Now shut everything down again, hook the preamp back up to the amp, and discon-
nect the source component from the preamp input. Once again use your shorting jack or trusty clip
lead, this time on the preamp input. Fire the system up and listen.
Let's assume that we hear the noise. OK, now we know that it's not the amp, not the source, so it
must be a problem in the preamp.
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