8902A-14
SUPERSEDES: None
DATE: 04 August 1992
8902A Measuring Receiver
Serial Numbers: 3122A02709 / 3122A02984
Problem with TRFL Measurements using Track-Mode Tuning
Parts Required:
0160-4807 Capacitor, Ceramic 33pF 100V
Situation:
A problem has been noted with certain 8902As (serial numbers noted above) while performing Tuned RF Level (TRFL) measurements using track-mode tuning. Track-mode
tuning is used with TRFL to make low-level measurements of drifting signals. The failure
can only be observed by enabling Special Function 32.9. Failure symptoms appear as an
inability to properly track drifting low-level signals or loss of phase-lock onto the RF
input signal while this mode of operation is enabled.
The problem is caused by a transistor (A4Q9) in the precision limiter circuitry of the FM
Demodulator which breaks into oscillation. This oscillation causes errors in the output
voltage of the FM discriminator which is used to re-tune the LO when Track-mode tuning
is enabled. Installing an AC ground at the collector of this transistor eliminates the oscillation.
1 of 2
AUTHOR: LHL
ENTITY: 1000
© 1992 AGILENT TECHNOLOGIES
PRINTED IN U.S.A.
SERVICE NOTE
ADMINISTRATIVE INFORMATION
MODIFICATION RECOMMENDED
SERVICE NOTE CLASSIFICATION:
ACTION
CATEGORY:
LOCATION
CATEGORY:
CUSTOMER INSTALLABLE
ON-SITE
SERVICE CENTER
AGILENT RESPONSIBLE UNTIL: 01 October 1996
ADDITIONAL INFORMATION:
IMMEDIATELY
ON SPECIFIED FAILURE
AGREEABLE TIME
AVAILABILITY:
PRODUCT’S SUPPORT LIFE
RETURN
SCRAP
SEE TEXT
SERVICE
INVENTORY:
RETURN
SCRAP
SEE TEXT
USED
PARTS:
STANDARDS:
Labor 2.0 Hour
Continued
Page 2 Service Note 8902A-14
Solution/Action:
Install a 33 pF capacitor on the backside of the A4 assembly from the collector of Q9 to
the positive (+) end of C36. Insure that the lead length is kept as short as possible. Refer
to the component locator diagram for the A4 assembly which is located on the back of
Service Sheet 10 in the 8902A Service Manual, Volume 3. Re-adjustment of the tracktune mode offset (Adjustment 7, 8902A Operation/Calibration manual) is required. Recalibration is not required.
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