Service manual

8-16 11713A Operating and Service Manual

Servicing the Attenuator/Switch Driver

Troubleshooting the A3 Latch Assembly

The A3 latch assembly contains 10 J-K flip-flops and a power-up circuit.

To Troubleshoot the A3 Latch Assembly

1. If any of the following conditions cannot be met, replace the A3 latch

assembly.

a. Turn the power off and then turn it on again. All attenuator lights

and the local light should be on.

b. Press each attenuator switch. Only the corresponding light

should turn off. No other light should flicker or change status.

c. Send a remote command to turn the attenuators off and then on.

All attenuators should come on.

d. Send a remote command to individually control each light

OFF/ON. Only the corresponding light should turn off. No other

fight should flicker or change status.

2. If these tests are inconclusive, test the Al interconnect, A7 switch,

AS GPIB, and A4 remote local logic board assemblies in this

sequence before replacing the A3 latch assembly.

Assembly Overview

When the driver is in the local mode, the J and K inputs to all ten

flip-flops are in the logic high state. The flip-flops then operate as

"toggle" flip-flops and respond to the front panel pushbuttons. The

pushbuttons function as clock pulses for the flip-flops.

In the remote state, the A4 assembly A or B flip-flop controls the J, K

inputs. In the A state, the J inputs are in the logic low state and the K

inputs are logic high.

The decoder on the A4 assembly generates the clock pulses for each

flip-flop. In the A state, flip-flops 1 through 10 are set so the Q = 1 and

NQ = 0. In the B state J inputs = 1 and K inputs = 0. Clock impulses

from the decoder set flip-flops 1 through 10 on the negative edge as

commanded by the bus.

The power-up circuit sets the state of all flip-flops so that the

instrument powers up in the local state and with all switches set to the

A (LEDs on) condition. Any attenuators connected to the driver are set

to maximum attenuation on power up.