Power Supply - Wavetek 39A Maintenance Manual

Trigger Generator
This is created by a counter-timer in IC10. The counter-timer produces a squarewave in the range
100kHz to 0.005Hz. The FPGA, IC221, may be set to use this as the internal trigger.

Power Supply

The transformer has two separate secondaries; one provides ± 15V by IC30 and IC31, the other
provides +5V by low drop-out regulator IC32 and −5V by IC33. The display backlight is driven by
a current source made up of Q22 and associated components and is approximately 150mA. IC34
provides local regulation for the +5V analogue. IC204 provides local regulation for the VCO.
IC226 provides local regulation for the PLL. PJ5 is a test point for the supply rails. Four PCB
mounted fuses protect the transformer secondaries under fault conditions.
Required values measured at PJ5:
Waveform DAC and Filters
IC210 is a high speed 12-bit DAC whose data is latched on the rising edge of DACCLK. The
output current is 20mA fullscale giving 1Vp-p into 50Ω, from 0V to −1V. The DAC has an internal
−1.23V (−1.27V to −1.17V) reference. R218 sets the full-scale output current. An internal control
amplifier mirrors this with respect to the −5V rail.
L201,L202,L203 and associated components form the 16MHz 7-stage elliptic filter. The inductors
are factory set before board assembly and must not be adjusted. L204 provides sinx/x correction
and is adjusted at initial calibration.
L205,L206,L207 and associated components form the 10MHz 7-stage elliptic filter. The inductors
are factory set before board assembly and must not be adjusted. L208 provides sinx/x correction
and is adjusted at initial calibration.
L209, C252 and C253 form a Bessel filter. L209 is also factory preset.
Amplitude Control, Sum and Modulation
IC215 is a 4-quadrant multiplier driven differentially via IC211. The main signal is at M and is 0V
to −1V; a dc reference, M1, of half this is generated by IC200-A. Amplitude is controlled by
IC218-A; with the output set to maximum the voltage at its output is approximately 1V.
External AM is selected by IC214-A and is summed with the amplitude control voltage at the input
of IC218-A.
Sum is selected by IC214-C and the external signal is summed at the multiplier output via its
Z input.
IC212 and IC213 form the sum input attenuator.
Amplifiers and Attenuators
With the amplitude at maximum the signal at the output of the multiplier is approximately 1Vp-p.
IC219 gives a gain of 5.5 to give 5.5Vp-p and IC220 gives a gain of 3.8 to give 20Vp-p.
IC218-B provides DC offset for the main output; when set to maximum, i.e. +10V, IC218-B's
output will be approximately −10V and its input approximately –3.6V.
Relays RL201 and RL202 select 20dB output attenuators and IC217 selects an intermediate
−10dB attenuator.
16
pin 1: +5VCPU ± 0.2V
pin 2: 0V
pin 3: −5V ± 0.2V
pin 4: −15V ± 0.6V
pin 5: +5VA ± 0.2V
pin 6: +15V ± 0.6V