RB1
16
TROUBLESHOOTING GUIDE:
If your RB1 does not work at all, recheck the following:
correct orientation of diodes, electrolytic capacitors, ICs and transistors.
resistor color codes; 2.2K and 22K resistors are easily confused. The
orange and red color bands look the same under certain conditions. This is
also true for 4.7K and 47K resistors.
soldering; solder bridges and cold solder joints are two of the most common
problems we see on kits returned for repair. You shouldn’t need a
magnifying glass. If a connection is suspect, resolder it!
the power supply; make sure you have 12 volts and if you’re using a DC
supply, be sure that the tip is positive.
If you have given your kit a thorough visual inspection, touched up any solder
connections that look less than perfect, and still haven’t found the problem, you
are ready for some more serious troubleshooting. There are several points that
can be checked with a voltmeter or an oscilloscope and may lead you to the
problem. If you have no test equipment of any kind and can’t borrow a meter
from someone, move on to the warranty section at the back of the manual. If
you have a voltmeter you can check the following:
Across the speaker terminals you should see about 12 to 15 VRMS. If you
get any reading move on to the next step.
You can check the output of U1 on pin 3. On AC, the voltage will vary from
0.4 to 2.2 VRMS. On DC, the voltage will vary from 0.2 to 10.5 VDC. The
best way to see what is happening is to check pin 3 with an oscilloscope.
You should see a square wave from zero (0) to twelve (12) volts (or source
voltage if you’re using something other than a 12 volt input) with a period of
two (2) seconds.
If the output of U1 is good, check the output of U2 at pin 7. You should have
about 6 VDC, or approximately 11.5 vpp (AC volts will be changing
constantly. On the oscilloscope you will see a square wave, 0 to 12 (or
source) volts that is sweeping back and forth. The period of the wave will
depend on the frequency setting at S2. If the square wave is not sweeping
but is steady, the problem is in or around the NE555 IC.
The same signal seen on pin 7 of U2 should also be on pin 3 and pin 11 of U3.
If you have a good signal at pin 3 and not at pin 11, U3 may be bad. If you have
a good signal at pin 11 and nothing across the speaker terminals, the problem
is centered around the speaker - Q1, 2, 3, or 4 or R12, 13, 14, or 15.
