BY SAM GOLDWASSER
Repairing Remote Controls
helping others on the Internet news-
ELCOME TO THE FIRST INSTALLMENT OF THE ALL
groups; writing the Internet repair and
troubleshooting guides mentioned above,
W NEW SERVICE CLINIC. AS YOU CAN SEE FROM THE
as well as other articles; providing free
BYLINE, MY NAME IS SAM GOLDWASSER. THOSE OF YOU THAT repairs for those who cannot afford pro-
fessional service; and doing other things
FREQUENT THE INTERNET MIGHT BE FAMILIAR WITH MY ONLINE that I find interesting. For now, this is
more fun and much more rewarding than
repair and troubleshooting guides, locat- curiosity and unending search for chal- a real job.
ed at lenges continue to this day. With that out of the way, lets turn to
ipg/REPAIR/, and mirrored at several After a long and varied career in engi- our first topic.
sites around the world. If not, perhaps a neering, teaching, and business, these
little introduction would be in order. days I am an independent engineering Remote Control Repair
An electrical engineer by profession, I consultant, but spend much of my time Fifteen years ago, a wireless remote
have always had a passion for fixing
mechanical and electronic devices. As a
kid, household appliances represented the
beginning of my fascination with technol-
ogy. It wasn t long before the workings of
the TV were of more interest to me than
the shows on its screen. Naturally I had to
see what was inside everything. Fairly
soon, I figured out that getting things
back together again was generally not that
much more difficult than disassembling
them in the first place. That insatiable
PHO
GND
FIG. 1 -THIS DETECTOR CIRCUIT
could be used for testing IR remote con-
trols, CD-player laser diodes, and other
low-level, near IR emitters. Component val-
ues are not critical. Test points are provided INSIDE A TYPICAL TV/VCR remote control transmitter. This schematic is for a unit made
for use with an oscilloscope. by Zenith.
control was a $50 or $100 option (in
1980 dollars) to a TV or VCR. Early
units used ultrasonic or RF analog sig-
nals and could perform only limited
functions. You were lucky to get any-
thing beyond on/off, volume, and chan-
nel up/down.
Today, a remote control is standard
even with low-cost, basic electronic
equipment. Nearly all modern remotes
use Infra-Red (IR) light for digital data
transmission. Some have more buttons
and functions than a personal computer!
Unfortunately, those added features and
functions sometimes come with a bur-
den of its own-many remotes have row
upon row of tiny, identical size buttons
with no logical layout of functions. On
the other hand, some are masterpieces of
ergonomic engineering, almost operat-
ing by themselves.
There are two kinds of problems with
remotes:
1. They seem to have legs of their
own and disappear at the most inconve-
nient times.
2. They get abused by being dropped,
dunked in Coke or beer, or chewed on
by the pet tiger, or are left alone to
develop dead, leaky batteries.
While there are some remotes that
will respond to a whistle and beep back
to identify their locations, most are the
ordinary deaf, dumb, and blind variety.
Unfortunately, I can not help you locate
your missing remote. If you suffer from
disappearing remote syndrome, a well-
designed universal remote-on a teth-
er-might make a good investment.
Fortunately, most actual problems
with remotes can be solved relatively
easily. First of all, it is important to rec-
ognize that most failures are of a physi-
cal nature. Since remotes operate on low
voltages under non-stressful conditions,
spontaneous electronic failure is rela-
tively uncommon. In short, if you don t
abuse your remote control, it is likely to
go a long time between failures.
Testing Remotes
All troubleshooting begins with the
simplest steps. Start by eliminating the
obvious. First, confirm that your prob-
lem is not simply due to a selector
switch in the wrong position or an acci-
dental press of a key selecting VCR
instead of TV If your broken unit is a
universal type, make sure it has not sim-
ply forgotten its programming or
codes-reinitialize it. A common cause
of memory loss is the batteries failing
out or losing contact for an instant due can t fall upon the photodiode. Select a
to a fall or bump. photodiode that is sensitive to near IR
Also double check to be certain that (about 750 to 900 pm). You could also
you are using the correct remote. A lot salvage one from an optocoupler or pho-
of remotes look alike, and sometimes tosensor. Dead computer mice also use
remotes for similar equipment from the photodiodes that could be salvaged.
same manufacturer can not be swapped. Finally, a salvaged IR sensor module
Next, try to determine whether the from a TV or VCR might also be used as
problem is indeed in the remote itself and an IR detector. Those usually operate
not the controlled equipment. The easi- from a single supply (5 V to 12 V is typ-
est way to do that is to temporarily pro- ical) and output a clean demodulated
gram a universal remote to match your signal (you will not see the carrier, only
equipment. If that equipment then oper- the 1s and Os).
ates successfully, you can be pretty certain Once we are certain that the remote is
that the problem lies in the remote unit. at fault, it is time to see if we can repair it,
or if it is even worthwhile to do so.
Diagnosing the Problem Unfortunately, as we have used up all of
To narrow down the problem, use an our room for now, that s a topic that will
IR detector to determine if the remote is have to wait until next month. Until then,
emitting an IR signal when each button is you can visit the sci.electronics.repair
pressed. While such a device does not FAQ homepage which is located at
guarantee that the signal is correct, it http://www.paranoia.com/-filipg/REPAI
eliminates most common problems from R/. If you ve got comments or questions,
consideration. An IR detector card or an can e-mail them to me at
You
IR detector circuit (like the one shown in sam@stdavids.picker.com.
Fig. 1) is very handy for testing remote
controls and other IR emitters. Another
alternative is to use a camcorder: Some
camcorders are sensitive to IR as well and
will show a bright spot of light if aimed at
a working source of IR.
Modern remotes use a pulse-code-
modulated carrier to send the command.
A typical carrier frequency is around 36-
to 56-kHz, with each pulse consisting of
multiple cycles (e.g., 20 for each bit) of
that carrier. For buttons that repeat, typ-
ical rates are 10 to 20 Hz, and the entire
code might actually be sent only when
the button is first pressed with only a
repeat code sent while it is held down.
The carrier frequency and coding
schemes have apparently not been stan-
dardized and vary quite a bit, even from
device to device from the same manufac-
turer. Therefore, it is beyond the scope
of this document to enumerate them all.
If more information is needed or
desired, it is possible to monitor the
waveforms with an oscilloscope. That
could be done by monitoring internal
signals of the remote including certain
pins on the main IC as well as the LED
or its driver. A simpler approach would
be to monitor the signal across the tran-
sistor in the detector circuit of Fig. 1;
the schematic includes test points for
that purpose.
Speaking of the detector circuit, the
only important point to keep in mind
when building the circuit is to make sure
that the LED is placed so that its light
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