Page 36 - Troubleshooting Analog Circuits

Choosing the Right Equipment 23

often identify problems. You can also use the good circuits to make sure that your
specialized test equipment is working properly.

17. A sturdy, broad workbench. It should be equipped with a ground plane of metal that
you can easily connect to the power ground. The purpose of this ground plane is to
keep RF. 60-Hz, and all other noise from coupling into the circuit. Place insulating
cardboard between the bench and the circuit-under-test. so that nothing tends to short
to ground. Another way to prevent noise from interfering with the circuit is to use a
broad sheet of single-sided copper-clad board. Placed copper-side down and with a
ground wire soldered to the copper. it provides an alternate ground plane. To prevent
electrostatic-discharge (ESD) damage to CMOS circuits. you’ll need a wrist strap to
ground your body through 1 Ma.

18. Safety equipment. When working on medium- or high-power circuits that might
explode with considerable power in the case of a fault condition. you chould be
wearing safety goggles or glasses with safety lenses. Keep a fire extinguisher nearb!.
too.

19. A suitable hot soldering iron. If you have to solder or unsolder heavy busseh from
broad PC-board traces, use a big-enough iron or gun. For small and delicate traces
around ICs, a small tip is essential. And, be sure that the iron is hot enough. An eas!
way to delaminate a trace or pad, whether you want to or not, is to heat it for too long
a time. which might happen if your iron weren’t big enough or hot enough. (The old
Heathkit warnings not to use a hot iron became obsolete along with the germanium
transistor.) In some cases, a grounded soldering iron is required: in others. a portable
(ungrounded or rechargeable) soldering iron is ideal. Make sure you know whether
your iron is grounded or floating.

20. Tools for removing solder, such as solder wick or a solder sucker. You should be
comfortable with whatever tools you are using; a well-practiced technique is sonie-
times critical for getting good results. If you are working on static-sensitive compo-
nents, an antistatic solder-sucker is less likely to generate high voltages due to in-
ternal friction than is an ordinary solder-sucker. I have been cautioned that a large
solder-sucker may cause problems when working on narrow PC traces: in that case.
solder wick may be the better choice.

2 1. Hand tools. Among the tools you‘ll need are sharp diagonal nippers. suitable pliers.
screwdrivers. large cutters. wrenches, wire strippers. and a jack knife or ExactoThf
knife.

22. Signal leads, connectors. cables, BNC adapters, wires. clip leads, ball hooks. and
alligator clips-as needed. Scrimping and chintzing in this area can waste lots of
time: shaky leads can fall off or short out.

23. Freeze mist and a hair dryer. The freeze mist available in aerosol cans lets you
quickly cool individual components. A hair dryer lets you warm up a whole circuit.
You’ll want to know the dryer’s output air temperature because that’s the tempera-
ture to which you’ll be heating the components.
NOTE: Ideally we should not use cooling sprays based on chlorofluorocarbons
(CFCs), which are detrimental to the environment. I have a few cans that some
people would say I shouldn’t use. But what else should I d-send the can to the