>>>YOUR ELECTRONICS QUESTIONS ANSWERED HERE BY N&V READERS
general-purpose pushbutton switch to
the exposed ends. Take the remote
apart and check the switch first. Also,
I once found a bad battery connector.
Make sure you measure nine volts at
The receiver has stopped working
a few times. Each time, I found bad
electrolytic capacitors that have dried
out and lost their capacitance.
Replacing the bad ones usually fixed
the problem. If you don't have a
capacitor tester, you could just replace
all of the electrolytics; there are six in
the Sears receiver.
As an aid in troubleshooting, the
demodulated 52 Hz tone is coupled
back to the antenna for viewing on a
scope. You should see a 52 Hz
waveform when you press the remote
button. You will need to find the
circuit return on the receiver board for
the scope ground. It should be the
negative terminal of the main filter
capacitor — usually the largest
capacitor in physical size and
capacitance. I don't think you'll have
to get involved with troubleshooting
the RF section.
Harbor City, CA
#2 I would not try to repair the
original transmitter as most have
proprietary chips with no ID numbers.
I would instead check out a
transmitter/receiver such as what is
listed at www.seeedstudio.com/depot.
They have a tab for communications,
then subtab for wireless on their site.
The transmitter may fit inside the
old transmitter case; the receivers
have relays which can be connected
to the manual button leads on the
garage door opener. Many other sites
have the transmitters/receivers which
are similar, but I have ordered from
Seeedstudio in the past successfully.
[#12103 - December 2010]
CONAR 251 Scope Info
Where can I find out the value of a
fuse for the CONAR Model 251
oscilloscope and/or where can I get a
manual or schematic for this scope?
(CONAR was bought out by the
National Radio Institute - McGraw Hill
Continued Education which is no
longer in business.) I want to power up
this scope and test its output. I need
the fuse type and amps before I test it,
as money is in short supply. Or, is there
a website to find this information?
The fuse in my oscilloscope is
labeled "BUSS MDL 1" on one end,
"250 VOLT" on the other. The manual
says the fuse is a one amp slow blow.
I have two manuals: one is for
assembly, the other is for operation.
This oscilloscope was part of an NRI
course, ca. 1980.
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