Motorola SSETM 5000 - Manual (Page 126)

November 11, 2004 6881094C12-A
9-22 Troubleshooting Charts: RX RF
RX RF—Page 3
TP502
= 0 Vdc?
No
No
Yes
Yes
Repair
defects
Measure RF levels at first preselector
filter and compute filter loss.
UHF: TP13, U401-3
No
Yes
Loss < 3 db?
Measure RF levels at LNA
and compute LNA gain.
UHF: U401-1, TP402
Measure RF levels at second preselector
filter and compute filter loss.
UHF: TP402, TP403
Gain
about
+12 dB?
2
6
No
Yes
Measure RF and IF level at mixer
and compute mixer conversion gain.
UHF: TP403, TP404
Loss
< 3 dB?
8
No
Yes
Measure
control voltage
at TP502
No
Yes
Fvco
too low?
UHF: < 71.1 MHz
Remove Abacus shield and
inspect second LO VCO.
UHF: SH501
TP502
= 5 Vdc?
3
5
5
No
Yes
Replace
Varactor D550
Check
LNA
Check
mixer
Visual
examination
OK?
No
Yes
Measure IF level at XTAL filter
and compute XTAL filter loss.
UHF: TP404, TP12
Mixer
gain about
4 dB? No
Yes
No problem
found
Loss
< 3 dB?
7
MAEPF-27472-B
TP502
(Vdc)
TP501
(MHz)
Fvco
1.7
3.7 71.1
75.6
UHF R1