Vectronics VEC-131K - Manual (Page 30)

VEC-131K Owner's Manual Aircraft Receiver Kit
28
aircraft radio systems. The flight crew is not authorized to grant passengers
permission to use radio devices while onboard.
IN CASE OF DIFFICULTY
In very rare instances is a defective component the source of a problem. Ninety-
five percent of the kits returned for factory repair are due to soldering problems
or parts in the wrong locations. We advise repeating the assembly instructions
step-by-step, looking for mistakes or soldering problems. Be especially wary of
electrolytic capacitors and semiconductors. Kit builders often miss obvious
mistakes. What is needed is a “fresh” set of eyes. Enlist a friend to go over
your work.
Always check the obvious! Is the battery dead, or have the battery leads been
accidentally reversed or broken? The speaker and antenna plug should be
carefully checked for shorted or open connections. Check the solder connections
for the antenna and speaker jacks—frequent removal and insertion may have
caused a solder joint to fatigue and open.
Look for clues to help you determine what stages are working, and which ones
may be in trouble. For example, if you can “peak” IF transformer L5 so
background noise, or hiss, is audible in the headphones or speaker, you know
that the audio stages and IF stages are probably working. That’s well over half
of the radio! The problem is probably in the LO, mixer or LNA stage.
You can “prove” the LO is working by using one of the alignment techniques
involving a frequency counter or monitor receiver. The only remaining stages
that may be in trouble at this point are between the antenna jack and the mixer.
See if this general checklist helps isolate your problem:
Does not turn on:
Check battery condition, snap clip, and power leads. Also, make sure lead
polarity is correct (red to +, black to GND). Make sure power switch is "on".
Check operating voltages.
Turns on, does not receive signals:
Check antenna, antenna lead, and plug for shorted or open condition. Also,
radios may not pick up signals in metal building without an outdoor antenna.
Drifts off-frequency rapidly, "motorboats", weak audio:
Symptoms of a weak battery or insufficient operating voltage. Be sure to check
battery voltage "under load" (with the radio turned on).