Rx Rf - Motorola ASTRO XTS 5000 Detailed Service Manual

Troubleshooting Charts: RX RF
RX RF—Page 3
2
Measure RF levels at first preselector
filter and compute filter loss.
VHF & UHF2: TP401, TP9
UHF: TP13, U401-3
700-800: TP13, D401-3
Loss < 3 db?
Yes
Measure RF levels at LNA
and compute LNA gain.
VHF & UHF2: TP9, TP12
UHF: U401-1, TP402
700-800: D401-3, TP402
Gain
about
+12 dB?
Yes
Measure RF levels at second preselector
filter and compute filter loss.
VHF & UHF2: TP12, TP451
UHF: TP402, TP403
700-800: TP402, TP403
Loss
< 3 dB?
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
Mixer
gain about
4 dB?
Yes
6881094C31-D
control voltage
No
6 VHF: < 42.6 MHz
UHF R1/R2: < 71.1 MHz
< 107.4 MHz
No
Check Remove Abacus shield and
LNA
inspect second LO VCO.
VHF & UHF2: SH502
UHF R1/R2: SH501
700-800: SH501
examination
No
8
Varactor D550
(D551 for UHF R2)
Measure IF level at XTAL filter
and compute XTAL filter loss.
VHF & UHF2: TP15, TP455
No Check
mixer
3
VHF
TP502 TP18 TP502
(Vdc) (MHz) (Vdc)
Fvco
Measure
1.40 42.6
3.20 47.1
at TP502
Fvco
too low?
No
= 0 Vdc?
700-800:
Yes
TP502 No
5
= 5 Vdc?
Yes
Visual
No Repair
defects
OK?
Yes
Replace
UHF R1: TP404, TP12
700-800: TP404, TP12
No
Loss
< 3 dB?
Yes
No problem
found
MAEPF-27472-C
UHF R1 UHF R2 700-800 MHz
TP502
TP501 TP502 TP501
(Vdc)
(MHz) (Vdc) (MHz)
Fvco
Fvco
0.00
71.1
71.1
1.85
75.6 75.6
4.30
5.00
No
TP502
5
Yes
7
July 21, 2004
5-25
TP501
(MHz)
Fvco
101.0
107.4
111.9
113.0