FM-100 Page 49
TROUBLESHOOTING
PROBLEM: Nothing happens at all when I turn it on.
SOLUTION: Check your fuse. If it is blown you will want to check section L for
rear panel wiring or section K for the power supply. Use a volt meter to check
your power supply voltages. Verify that there is +8, +5, and -8 volts on the out-
puts of the regulators. Also check U2 pin 3 for a 1.5MHz clock signal.
PROBLEM: Everything works, but only some or no lights light up on the front.
SOLUTION: Check section A and make sure you put your LED displays in the
correct way. Also check your 5 wire jumpers for correct installation.
PROBLEM: I can’t get the FREQ LOCK LED to light and I can’t pick up the
signal on the receiver.
SOLUTION: You will definitely want to check your parts placement in section
G for misplaced components. Check the voltage on R11, if it is less than 0.2
or greater than 4.8 and L1 doesn’t have any effect then the VCO may not be
oscillating. Make sure the crystal is 6.00MHz. Check around Q2 and D10. Also
check C11 for proper orientation.
PROBLEM: One channel out completely, other one sounds OK.
SOLUTION: More than likely a short somewhere in any one of the audio sec-
tions. These are usually a bugger to find without a signal tracer or an oscillo-
scope. Inject a signal into both sides and trace through the circuit. Compare
one channel to the other all the way through the circuit until one side is not
present. You can bet you can now locate the problem.
PROBLEM: Very distorted sound.
SOLUTION: Turn down your level controls. If that does not help, check your
power supply voltages. If a negative or positive supply is not there, the signal
will be lousy.
PROBLEM: Transformer gets hot.
SOLUTION: Ignore it. Transformers are made to run hot at their maximum rat-
ings and we are running close to it with our unit. Don’t worry, we have given it
many long term tests to make sure it doesn’t burn the house down! Of course
if it does singe your hand, there may be a problem in the power supply. Give it
a check, especially the capacitor and regulator orientation.
PROBLEM: Lots of AC hum in the audio on the tuner.
SOLUTION: Again check your power supply. If there is a heavy load due to a
faulty circuit somewhere, the power regulators won’t regulate, letting raw DC
into the audio circuits.
PROBLEM: Still lots of AC hum in the audio.
