Vectronics VEC-1016K, Руководство пользователя, Страница: 21 / 23

[ ] Squelch won't open when control is fully counter-clockwise: Check the value of
the squelch potentiometer. It must be 100K. If a 10K pot is installed at R10, the squelch
won't open.
[ ] Poor sensitivity: Look for antenna problems. Also, check condition of L1, L2. If
they are improperly shaped or if a lead is broken, sensitivity will be poor.
If these checks fail to uncover the problem, repeat the "QC" check one more time.
Service records show that, for most malfunctioning kits, outright component failure is
relatively rare. In most cases, the culprit is a misplaced part, reverse-polarized capacitor
or diode, or a faulty solder connection!
Voltage Analysis: One effective way to pin-point where a circuit problem might be is to
use voltage analysis. To do this, you'll need a voltmeter--preferably a high-impedance
DMM type. Set your meter to the 10-volt dc range and clip the black (-) test lead to a
ground point on the PC board (the frame of the antenna connector is a good point).
Make sure the radio's battery is fresh--the chart readings were made using a 9.0-volt
power source. Using the red (+) lead, check the voltage on each IC pin and compare it
against the voltage chart below. Readings should be within 10-15% of chart value:
U1, MC13135 U2, MC34119 Q1
Pin Voltage Pin Voltage Pin Voltage E B C
1 5.2 13 5.2 1 0.1* 0 .77 7.1
2 4.5 14 0.1* 2 4.0
3 4.3 15 0.1* 3 4.0
4 5.2 16 0 4 4.0
5 4.7 17 2.3 5 4.0
6 5.2 18 5.2 6 8.8
7 3.8 19 5.2 7 0
8 0 20 4.0 8 4.0
9 4.4 21 5.2
10 4.4 22 5.2
11 4.4 23 1.2-3.0
12 .2 (no sig) 24 0
*This represents the squelch-open or "logic-low" voltage. When squelch is closed
(receiver muted), voltage becomes 3.8 volts, or "logic-high").
If you find one or more pins that read radically different from the chart value, it may
indicate the device is bad--or it may mean a circuit problem exists in that portion of the
radio. If you have technical skills and can read a schematic diagram, this will help you.
For example, if you get an unreasonable reading on pin 23 of U1, the schematic shows
that the radio's voltage-tuning circuitry is connected here. You might look for defective
or misplaced components on that portion of the circuit board as a potential cause. If,