Motorola SSETM 5000 service manual Lna

9-22 Troubleshooting Charts: RX RF

RX RF—Page 3

2

Measure RF levels at first preselector

filter and compute filter loss.

UHF: TP13, U401-3

No

Loss < 3 db? 6

Yes

Measure RF levels at LNA

and compute LNA gain. UHF: U401-1, TP402

Gain		No	Check
about
			LNA
+12 dB?
	Yes

Measure RF levels at second preselector

filter and compute filter loss.

UHF: TP402, TP403

Loss	No	8
< 3 dB?

Yes

Measure RF and IF level at mixer and compute mixer conversion gain. UHF: TP403, TP404

Mixer	No	Check
gain about
		mixer
4 dB?
Yes

3		UHF R1
	TP502		TP501
	(Vdc)		(MHz)
Measure			Fvco
	1.7		71.1
control voltage
at TP502	3.7		75.6

Fvco			No		No
too low?				TP502		5
UHF: < 71.1 MHz				= 0 Vdc?
	Yes			Yes
		No
TP502				5
= 5 Vdc?

Yes

Remove Abacus shield and inspect second LO VCO.

UHF: SH501

Visual No Repair

examination defects OK?

Yes

Replace

Varactor D550

Measure IF level at XTAL filter and compute XTAL filter loss.

UHF: TP404, TP12

Loss	No	7
< 3 dB?

Yes

No problem

found

MAEPF-27472-B

November 11, 2004 6881094C12-A