Flatness Control (Rf Gain Dacs) - Agilent Technologies 8564EC Service Manual

Flatness Control (RF Gain DACs)

Refer to function block M of A3 Interface Assembly Schematic Diagram
(sheet 4 of 6) in the 8560 E-Series Spectrum Analyzer Component Level
Information.
RF Gain DACs control the A15 assembly flatness compensation
amplifiers. The RF Gain DACs are arranged so that the output of one
DAC is the voltage reference for the other DAC. This results in an RF
GAIN voltage which is exponentially proportional to the DAC settings.
Each DAC is set to the same value. The A15 RF assembly converts the
RF GAIN signal to a current for driving the PIN diode attenuators in
the Flatness Compensation Amplifiers. The exponentially-varying
voltage compensates for the nonlinear resistance-versus-current
characteristic of the PIN diodes.
1. Place the WR PROT/WR ENA jumper on the A2 controller assembly
in the WR ENA position.
2. Press ,
CAL MORE 1 OF 2
. Press
FLATNESS DATA
displayed.
3. Press the key until DATA @ 300 MHz is displayed. Note the
number directly below DATA @ 300 MHz this is the RF Gain DAC
value.
4. Connect a positive DVM lead to A3J400 pin 13 and the negative
DVM lead to A3TP4.
Check that the DVM reading increases from near 0 Vdc to between
5.
−1.3 and −1.9 Vdc as the RF Gain DAC setting is increased from
0 to 4095.
6. If the DVM readings are incorrect, press
,
MORE 1 OF 2 SERVICE CAL DATA
Press
NEXT BAND
key until DATA @ 300 MHz is displayed. Proceed as follows:
a. Check the +10 V reference.
b. Check for narrow, low-going pulses at A3U417 pin 13 (LWRCLK).
c. While rotating the front-panel knob, check for narrow, low-going
pulses at A3U417 pin 1 (LDAC1) and pin 14 (LDACU1).
d. While rotating the front-panel knob, check for narrow, low-going
pulses at U417 pin 16 (L_IA0) and pin 15 (IA4).
7. If the LWRCLK, LDAC1, or LDACU1 is incorrect, refer to the
Interface Strobe Select block in this chapter.
Chapter 8
,
SERVICE CAL DATA
until FLATNESS BAND # 0 is
NEXT BAND
,
FLATNESS
until FLATNESS BAND # 0 is displayed. Press the
ADC/Interface Section

Flatness Control (RF Gain DACs)

, , and
FLATNESS
, ,
PRESET SGL SWP CAL
, and
FLATNESS DATA
,
.
389