Ramsey Electronics FX Series Manual page 128

VCO & PLL Faults:
(manual pages 21-24, 82 - 89, 90 - 97)
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.
VOLTAGES ON U6 @ 223.5 MHZ IN RECEIVE/TRANSMIT
pin ~ VDC
20 ~ 5/5
19 ~ 0/0
18 ~ 5/5
17 ~ 5/0
b. Check VCO for proper range of operation. Follow the test on page
assm. 86-87 of your manual. (You will need to remove R47 for this
test) The VCO should tune smoothly from approx. 220 Mhz to 260
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.
c. 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 back to the
manual, isn't our "n" number for 10 Khz right about 2? Some
coincidence! Now we can guess that our fault is between the # 2
position trace and the input to U6.)
pin ~ VDC
16 ~ 5/5
15 ~ 5/5
14 ~ 5/5
13 ~ 5/0
pin ~ VDC
12 ~ 0/5
11 ~ 5/0
10 ~ 0/0
25 ~ 5/5
pin ~ VDC
24 ~ 0/5
22 ~ 5/5
21 ~ 0/0
23 ~ 0/0