FX 146
•
140
help after all.
VCO & PLL Faults:
(manual pages ref. 21-24, assm.35-36, 43-48, 52-57)
1.
PLL not locking. (L7 will not set correct voltage @ TP1)
a.
Check for proper programming inputs to U6 (pins 10-25). If
incorrect, fault lies between diode matrix and inputs to U6.
b.
Check VCO for proper range of operation. Follow the test on page
assm. 39-40 of your manual. (You will need to remove R47 for
this test) The VCO should tune smoothly from approx. 120 Mhz
to 180 Mhz as seen on TP2. If not, check area of Q7. TP3 should
indicate approx. 1/64 of the frequency at TP2. If not, check area of
U3.
*Common faults:
?
Solder shorts between traces.
?
Diodes installed in reverse.
?
Excess lead length on VCO components
?
Improper frequency readings. Try probing on other components,
(Q7, Q16, R113) for a better reading.
2.
VCO Frequency Incorrect.
a.
If frequency is incorrect on one channel only, recheck diode
programming for that channel.
b.
A few channels are off by the same amount. Check for similar
diode programming on these channels to find your faulty area.
(ex. Let’s say our faulty channels are all off by 10 Khz, and they
all use the # 2 diode programming position. Hmmm, if we refer
pin ~ VDC
pin ~ VDC
pin ~ VDC
pin ~ VDC
20 ~ 0/0
16 ~ 0/0
12 ~ 5/0
24 ~ 0/5
19 ~ 5/5
15 ~ 0/0
11 ~ 5/5
22 ~ 0/0
18 ~ 5/5
14 ~ 0/5
10 ~ 0/5
21 ~ 0/0
17 ~ 0/5
13 ~ 5/0
25 ~ 0/5
23 ~ 0/0
VOLTAGES ON U6 @ 146.52 MHZ IN RECEIVE/TRANSMIT
FX-146
•
7
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