Agilent Technologies 5517B Operation And Service Manual page 90

8-129. +15V and -15V are supplied by the system power supplies via the rear panel connector A1J2. Fuse A3F1
protects both the A3 digital and analog control circuits. The +5V is generated by regulator A3U7. A3CR2 protects
A3U7. A3C5 stabilizes A3U7 and A3C4 filters A3U7 +5V output. Output +15V is the supply after being filtered by
A3L2 and A3C11. A3L1 and A3C12 filter -15V. A3 capacitors C2, C6, CI6, CI 7, and C21 provide local decoupling of
the supplies.
8-130. A4 Sampler Board
8-131. The A4 Sampler Board connects to A3 Controller/Reference board. The only active component on A4 is
A4CR1, a photodiode that provides a signal to A3U11D (Pin 13) on A3. Pads on the underside of A4 connect to the
liquid crystal via two elastomeric connectors which project from the A6 Sampler Assembly. Liquid crystal operation
is discussed in the A3 theory section.
8-132. A3 CONTROLLER/REFERENCE BOARD TROUBLESHOOTING
8-133. Service information for the A3 Assembly is divided into the following procedures:
8-122. A3CR5 is reverse biased to reduce its capacitance. The +15V bias voltage is filtered by A3R46 and A3C27. A
polarizer, oriented at 45° to both optical frequency components, passes optical power at the reference frequency onto
A3CR5. The reference frequency is the difference in frequency between the two optical frequency components of the
laser beam.
8-123. A3U17 contains two amplifiers. The gain of the first amplifier is set by A3R44. The gain of the second
amplifier is fixed. A peak detector circuit charges A3C28 to a DC value proportional to the output of A3U17. With
nocurrent from the photo diode, the voltage on A3C28 is approximately equal to the voltage on A3C24. When
photodiode current is present, the change in voltage on A3C28 is the amplitude of the signal coming out of the
second amplifier. When the amplitude exceeds 100 mV, the voltage at A3U17 Pin 2 (~REF ON) drops to TTL low.
A3Q6, A3CR6 and A3R45 shift the output of A3U17 to TTL levels. A3 capacitors C22, C23, C24, C26 and C29 are
used for coupling and bypass. A TTL high on A3U17 Pin 11 (-LTO) gates off the reference frequency output and
raises A3U1 7 Pin 2 to Vcc.
8-124. Line Driver (K)
8-125. A3U16 provides the necessary power to output the reference frequency signal to the system electronics. A3L3
limits the current spikes in A3U16. The special grounding and decoupling of the line drivers and receivers prevent
crosstalk and oscillations.
8-126. Power-On Reset (POR) (G)
8-127. When power is turned on, or REF ON drops low during the locked state of the optical mode, the power-on
reset circuit sets the state machine in preheat state.
8-128. Laser Head Power Supply Conditioning (C)
8-129. +15V and -15V are supplied by the system power supplies via the rear panel connector A1J2. Fuse A3F1
protects both the A3 digital and analog control circuits. The +5V is generated by regulator A3U7. A3CR2 protects
A3U7. A3C5 stabilizes A3U7 and A3C4 filters A3U7 +5V output. Output +15V is the supply after being filtered by
A3L2 and A3C11. A3L1 and A3C12 filter -15V. A3 capacitors C2, C6, C16, C17, and C21 provide local decoupling of
the supplies.
8-130. A4 Sampler Board
8-131. The A4 Sampler Board connects to A3 Controller/Reference board. The only active component on A4 is
A4CR1, a photodiode that provides a signal to A3U11 D (Pin 13) on A3. Pads on the underside of A4 connect to the
liquid crystal via two elastomeric connectors which project from the A6 Sampler Assembly. Liquid crystal operation
is discussed in the A3 theory section.
8-132. A3 CONTROLLER/REFERENCE BOARD TROUBLESHOOTING