E4422B-01
SERVICE NOTE
SUPERSEDES: None
E4422B RF Signal Generator
Serial Numbers: 0000A00000/9999Z99999
(valid for all units with motherboards listed below)
Replacement Procedure for Q501 on Motherboard/CPU
Duplicate Service Notes:
E4400A-02, E4400B-01
E4420A-02, E4420B-01
E4421A-02, E4421B-01
E4422A-02, E4422B-01
E4430A-03, E4430B-01
E4431A-03, E4431B-01
E4432A-03, E4432B-01
E4433A-03, E4433B-01
To Be Performed By: Agilent-Qualified Personnel or Customer
Parts Required:
P/N Description Quantity
1854-0828 TIP-122 Transistor 1 (see text)
ADMINISTRATIVE INFORMATION
SERVICE NOTE CLASSIFICATION:
INFORMATION ONLY
AUTHOR:
JV
© 1999 AGILENT TECHNOLOGIES
PRINTED IN U.S.A.
ENTITY:
5320
Continued
DATE: March 1999
ADDITIONAL INFORMATION:
1 of 2
Page 2 Service Note E4422B-01
Situation:
A large proportion of motherboard failures have been caused by stress fractures internal to
Q501, the series-pass transistor for the +9 volt power supply.
Since replacement of the motherboard is complex and time consuming, it is best to first check
any motherboard failure for proper operation of this supply. If this supply should fail, Error
508 (Synthesizer unlocked) will be generated and no RF power will be seen. The +9 volt LED
(DS505) will not be lit, which is easily visible once the cover has been removed. In most
cases, replacement of this transistor will restore proper operation with no further
calibration required.
This problem only affects motherboards with the following part numbers:
E4400-60001
E4400-60124
E4400-60192
Solution / Action:
If the +9 volt LED is not lit, check the voltage on the leads of Q501. Remove the 15 screws
holding the bottom shield in place. Q501 is the TO-220 style transistor located on the
bottom side of the motherboard, at the front of the instrument, next to the front panel ribbon
cable connectors. Viewed with the mounting tab on top, the leads are BCE (left to right). The
base should be about +11 volts, the collector should be about +12 volts, and the emitter
should be about +9.5 volts. If the base or emitter voltages are incorrect, replace Q501.
Unscrew, then unsolder, the old defective transistor. Set aside the shoulder washer
(0340-1162) and screw (0515-0372) for later reuse.
Obtain a new transistor and bend all three leads with needle nose pliers as shown in the
drawing below. This may take some practice so it helps to order several replacement
transistors. This lead formation is done to prevent future failures caused by stress fractures.
Insert the transistor into the motherboard but do NOT solder it yet. Use the shoulder washer
and screw to fas ten th e t ra ns i st o r, maki n g su re th e sh ou l de r was h e r is pr op er l y se at e d. On ce
the transistor is mechanically secured, it may be soldered from either the top or bottom side of
the board. Using an ohmmeter, verify the transistor’s tab is not shorted to ground.
Apply power and verify the proper voltages are obtained and the LED is lit. Verify proper RF
output. If all is okay, reassemble the instrument. Make sure the bottom shield does not come
in contact with the raised leads of the transistor. For extra assurance against shorts, a small
piece of mylar tape, properly positioned, may be attached to the shield. No instrument
adjustments should be necessary.
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