Keithley 485 Instruction Manual page 40

5.6.3 Power Supply and Battery Pack (Modal 1766)
5.6.4 A/D Converter and Display
Checks
Table 5-4 shows the various checks that can be made to the
power supplies within the Model 465 and 1758. In addition to
the normal voltage checks, it is a good idea to check the
various supplies with an oscilloscope to make sure no noise is
present.
Make sure the A/D converter and display are operating prop-
erly before attempting to troubleshoot the signal conditioning
circuit. Check these circuits using the information in Table 5-5
and 58.
Table' 6-4. Power Supply Checks and Battery Pack (Modal 1758) Checks
r-
Step Item/Component
1 S102 Line Switch
2 FlOl Line Fuse
3 Line Cord
-I-
Remarks
5102 externally accessible from rear panel.
4 U121** Input (TPl)
5 U121"' Output (TP31
6 U122 Input fTP2)
7 U122 Output fTP4)
8 VR103
9 U107pin 8
lo* QlOl base
Required Condition
Set to 115 or 230V as required.
Continuity.
Plugged into line receptacle;
power on.
+12v flO%
+5v f5%
-20v to -14v
-lov flO%
-8.25V to -8.45V
-7v f5%
0.W while charging (power
switch off).
Line cord disconnected,
battery pack charged,
power switch on.
z 8.8V
+5V with batteries charged.
+ 5V regulator input.
+ 5V regulator output.
Negative supply input.
Negative supply output.
Reference zener diode.
Low noise negative supply.
Current sink.
ll* Battery' Pack
Voltage inverter.
Voltage comparator
12* UlOl pin 8
13* U102 pin 7
'These items are located on the Model 1758 (if installed).
**If U121 is replaced, be sure that the device is properly seated on the mother board so that it will not touch
the IEEE board (if installed).
Table 5-6. A/D Converter Checks
5-6
Item/Component\ Required Condition
/Turn on Dower: select 2mA
range. Engage ;ero check.
U120, pin 38 3.2788MHz Clock
U118, pin 10 655.38kHz Clock
U116, pin 6 81.92kHz Clock
U116, pin 5 40.98kHz Clock
U118, pin 7
163.84kHz Clock
U116, pin 12
1.28kHz Clock
U115, pin 6
+5V to -0V pulse train,
3pec duration every 22Gec.
U109, pin 8 Integrator Ramp
UllOB, pin 6 -1.5v
Ul 106, pin 7
Variable pulse train OV to + 5V.
U117A. pin 6 Variable pulse train, OV to + 5V.
U108B. pin 15
Variable pulse train, OV to f5V.
U108B, pin IO =5msec positive going pulses.
U117B. pin 9
IOOmsec positive going pulse.
Remarks
Crystal (YlOl)
Address Strobe
Synchronous Clock for AID
Synchronous Clock for A/D
Stnchronous Clock for AID
Integrator timebase and real time interrupt.
Charge balance synchronization signal.
Comparator Reference
Comparator Output
Reference current generator.
Control line for charge balance/single
slope.
Control line for integrator.