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Theory of Operation
3-92
2715 Spectrum Analyzer Service Manual
The CRT is biased as follows:
Cathode --2750 VDC
Heater --2750 VDC, 6.2 V
RMS
Grid --2880 VCO
Accelerator 24 VDC
Focus --2200 to --1925 VDC
Astigmatism 115 to 0 VDC
D3, D4 ave 24 VDC
D1, D2 45 VDC
Geo mesh 115 to 0 VDC
Anode 11000 VDC
TRACE ROT +30 mA to --30 mA
The voltage multiplier is encapsulated in high insulation material. Both cathode
and anode multipliers are AC coupled within the multiplier and have multiplica-
tion factors of --2 and +8, respectively.
The high voltage regulator circuit takes a sample voltage from the cathode and
controls the impedance of Q130 for a steady cathode voltage. The parallel
combination of C130 and Q130 (with R637) is switched into the high voltage
current loop when the voltage at pin 23 of T230 goes negative (CR531 turns off
and CR530 turns on). The positive DC voltage on C130 is added to the negative
excursion on the high voltage winding. Therefore, the total peak to peak voltage
seen at the input of the high voltage multiplier is the peak to peak voltage at the
transformer secondary minus the DC charge on C130. The high voltage outputs
are changed by varying the impedance of Q130, which discharges C130. VR530
and VR630 provide a 300 V clamp that protects C130, Q130, CR530, and
CR531 from overvoltage. The cathode has almost 300 V of regulation range.
NOTE. In instruments with serial numbers B030000 or above, C130, CR530,
CR531, Q130, VR530, and VR630 were changed to extend the cathode regula-
tion range to nearly 400V. Voltage regulators VR530 and VR630 provide a 460 V
clamp.
The Vertical Display circuit is a video amplifier (preamplifier and a paraphase
amplifier). Gain and DC offset (Vertical Position) are set so the signal at the
input of the paraphase amplifier swings from --0.7 V to +0.7 V for a full screen
signal. The output of the paraphase amplifier then drives the vertical deflection
plates.
Three signals may be applied to the Vertical Display circuitry:
H LOGVID (Detected video from the Log board)
H DSVER (from the Display Storage board)
H VIDVERT (Vertical Scan signal from the Sweep board)
Vertical Display