To Next Page

To Previous Page

Test 303.2 — LO OHM PATH

Bank DC/OHM

Inputs Open

Expected Value 12.4 volts

Limits 0.5 volts

Fault Message 13.3V SOURCE

Description

This test is similar to test 303.1. The +13.3V reference is switched to REF-

BOOT again by closing U133 pins 6 to 7. Q124 and Q126 are turned on by

setting the OHMA control line low. +14V is applied to R195, and since Q124

is on, +13.3V appears on the other end of R195. The voltage across R195

(70.6K

Ω

) is 0.7V. 10µA therefore ﬂows through R195, Q126, Q119, CR114,

and Q120 (/LOWOHM control line low).

The current (labeled OHM) then ﬂows through R304, U107, VR106, and

VR105 to LO. This is again the clamping circuit described in test 301.2. The

+12.4V reference is routed through Q104, to BUFCOM, and on to the A/D

MUX with a gain of

1. Measure +12.4V at AD_IN.

Bit patterns

Bit pattern Register

87654321

—U106—

110v1111

87654321

—U109—

00101111

87654321

—U134—

0v01001v

—U130—

10111101

87654321

—U121—

01100100

ACDC_STB

MUX_STB

IC pins: Q8=11, Q7=12, Q6=13, Q5=14, Q4=7, Q3=6, Q2=5, Q1=4

2-38 Troubleshooting

Keithley 2000 Repair Manual

Other manuals for Keithley 2000