6881094C31-E November 16, 2006
Troubleshooting Charts: RX RF 5-33
RX RF—Page 3
TP502
= 0 Vdc?
No
No
Yes
Yes
Repair
defects
Measure RF levels at first preselector
filter and compute filter loss.
VHF & UHF2: TP401, TP9
UHF: TP13, U401-3
700-800: TP13, D401-3
No
Yes
Loss < 3 db?
Measure RF levels at LNA
and compute LNA gain.
VHF & UHF2: TP9, TP12
UHF: U401-1, TP402
700-800: D401-3, TP402
Measure RF levels at second preselector
filter and compute filter loss.
VHF & UHF2: TP12, TP451
UHF: TP402, TP403
700-800: TP402, TP403
Gain
about
+12 dB?
2
6
No
Yes
Measure RF and IF level at mixer
and compute mixer conversion gain.
VHF & UHF2: TP451, TP15
UHF R1: TP403, TP404
700-800: TP403, TP404
Loss
< 3 dB?
8
No
Yes
Measure
control voltage
at TP502
No
Yes
Fvco
too low?
VHF: < 42.6 MHz
UHF R1/R2: < 71.1 MHz
700-800:
< 107.4 MHz
Remove Abacus shield and
inspect second LO VCO.
VHF & UHF2: SH502
UHF R1/R2: SH501
700-800: SH501
TP502
= 5 Vdc?
3
5
5
No
Yes
Replace
Varactor D550
(D551 for UHF R2)
Check
LNA
Check
mixer
Visual
examination
OK?
No
Yes
Measure IF level at XTAL filter
and compute XTAL filter loss.
VHF & UHF2: TP15, TP455
UHF R1: TP404, TP12
700-800: TP404, TP12
Mixer
gain about
4 dB?
No
Yes
No problem
found
Loss
< 3 dB?
7
MAEPF-27472-C
TP502
(Vdc)
TP501
(MHz)
Fvco
1.7
3.7
71.1
75.6
UHF R1
TP502
(Vdc)
TP18
(MHz)
Fvco
1.40
3.20
42.6
47.1
TP502
(Vdc)
TP50
(MHz
Fvco
0.00
1.85
4.30
5.00
101.0
107.4
111.9
113.0
700-800 MHz
VHF
TP502
(Vdc)
TP501
(MHz)
Fvco
1.57
3.11
71.1
75.6
UHF R2
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