FM Tuner Problem
Thu, 9 Mar 2006 22:31:10 -0800
The FM Tuner on my recently-acquired Harmon-Kardon 430 doesn't work. No
audio at all -- no static or anything. The AM side of the tuner works
Nothing is visibly broken inside. I looked at the service manual for a
while, but I'm not sure where to start. If anyone's interested, here's
There's an adjustment knob for the FM muting in the back of the unit,
with this knob in the right position and with FM muting turned on, I
can get a signal, albeit quiet and muffled-sounding. Another
interesting quirk is that it goes silent again if I touch a screwdriver
to a certain part of the FM Front End.
Anyone have any idea what's going on? I'm a reasonably technical person
and I love to learn new things, so I'd like to think I can fix this. On
the other hand, I'm not really sure where to start, and I've heard that
FM Front End repairs can be a little tricky.
Any help would be much appreciated!
You had better limit yourself to measuring voltages at the test points
listed in your service manual. Without the needed FM signal generator and a
good oscilloscope, all you could do by attempting adjustments would be to
make things much much worse.
However, there is no good reason for a front end failure other than
oxidation of switch contacts or cold solder joints that finally quit
working. Failure of transistors normally happens after high load stress,
not likely found in this application. Clean up all mechanical parts and
check for circuit board loose connections and damage. Use the voltage chart
to find sections that seem out of spec to concentrate your cleaning efforts.