Vectronics VEC-1012K User Manual
Page 24
VEC-1012K Owner’s Manual
24
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,
and L3. 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:
MC13135 (U1)
MC34119
(U2)
2SC2498
(Q1)
Pin Voltage Pin Voltage Pin Voltage E B C
1 5.2 13 5.2 1 0.1*
.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
*Squelch open voltage (becomes 3.8 when squelch is "logic-high" or closed)
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