Circuit Board Checks; Display Board Checks; Table - Keithley 6517 Service Manual

Electrometer

Table of Contents

Troubleshooting

Voltage source

The various voltage source circuits include the digital inter-

face, the DAC, range control, and the power output stage.

Each of these sections is brieﬂy discussed below.

Serial voltage source control information is converted into

parallel form by U303-U306. U304 is a latch that stores

range and operate information, while U305 and U306 store

the 16-bit data word for the voltage source output value.

The 16-bit data word that represents the voltage source value

is converted into analog form by U308, a 16-bit DAC. The

voltage reference for U308 is generated by regulator U309.

The voltage source itself is actually a compound operational

ampliﬁer. U307 provides the overall stage gain, while power

output capabilities are supplied by Q311-Q317. Note that the

±120V supply is used to power the output stage on the 100V

range, while the ±1200V supply powers the output stage on

the 1000V range.

Table 5-2

Display board checks

Step Item/component

FRONT PANEL TESTS

P1033, pin 5

CR902 cathode

P1033, pin 12

U902, pin 43

P1033, pin 10

P1033, pin 8

5-10

Required condition

Verify that all pixels operate

+5V, ±5%

+60V, ±10%

Goes low brieﬂy on power-up, then goes high

4MHz square wave

Pulse train every 1msec

Brief pulse train when front panel key pressed.

Voltage source ranging is provided by selecting feedback

resistor values with elements of U312. Approximate voltage

gain on the 100V range is × 20.5, while the 1000V range gain

is × 207.9.

5.6