Nanovoltpreamptroubleshooting; Dc Volts Attenuator Troubleshooting; Diacircuittroubleshooting - Keithley 181 Service Manual

MAINTENANCE
MODEL 181
5-25. Nanovolt Preemp Troubleshooting
The Nanovolt Preamp Operation is explained in the Theory of
Operation. It is recommended that the troubleshooter read the
Nanovolt Preamp section of the Theory of Operation before
troubleshooting the Preamp. The following Table 56 is a step
by step procedure to breakdown and isolate the problem
quickly and easily.
FIGURE 5-22. Quiet U401 lOpV/cm 5Omsfcm
5-29. DC Volts Attenuator Troubleshooting
The DC Volts Attenuator is made up of a precision voltage
divider iR313A. B, C and D, R314, R315, R309, R3lO and
R3111, ranging relays iK301 and K3021 and input protection
FETs ID301 and Q3021. The Attenuator is located on the
Analog Board PC-529. The Attenuator divides the input signal
1" the appropriate switching FET.
5-W. IEEE Bus Circuit Troubleshooting
Bus address toggle switches iS103) set the Bus address, The
address cannot be changed while power is applied, To change
this address, select new address by 5103 and cycle the poww
Visually check the 181 display to see that it is "peratlng
properly. If it is nonfunctional, flickering or displaying
incorrect data then check the display circuit UllO, "201.
U202, U203, Q201-0208. If the display is "perat,ng
properly, then proceed to Step 2.
Program the controller to input any command string and
output data. Check buffers U133 and U134 for input and
output of data. Check T/R1 (Pin 271 and T/R2 IPin 281 of
U131 for toggling 10 to 5V switching).
Check t" see that tha Bus Address can he changed, Turn
off the instrument and toggle in a different Bus Address.
Turn power on and see that the new Bus Address is
present by appropriate controller address.
5-31. DIA Circuit Troubleshooting
Visually check the 181 display t" see if it is cperatlng
properly. If it is nonfunctional, flickering or displaying
incorrect data then check the display circuit UllO, U201,
U202, U203. 0201-0208~ If the display is operating
properly, then proceed to Stop 2.
Input a ramp voltage of -2V t" +2V at a .5Hz rate f" the
Banana Jacks on the 2V range. Using an oscilloscope
measure the signals located on Pins 4-15 of Ull7. The
signals should he switching from 0 volts to + Svoits (f"ggl~
ingl. This should be done with the Analog Output Gain
Switch t" Xl. If the pinsare toggling proceed to theanalog
section of the D/A circuit. If the pins are not toggling pr"~
teed t" Step 3.
Monitor bits 1~4 of "117 to see that they are toggling. If
they are not toggling, check UllO. If the pins are toggling,
then proceed to Step 4.
Monitor bits 5-12 of U117 to see that they are toggling~ If
they are not toggling and Pin 11 (Enable of U1161 is
toggling, then Ul16 is had. If Pin 11 (Enable of 1161 is not
toggling, then check UllO. if Pin 5~12 of U117are toggling,
then the digital section of the D/A circuit is functioning
properly.
5.32. Switch Input Section Troubleshooting
The switch input section is shown on Schematic 30583D.
Sheet 2 of 2 and consists of UlM, Q102, RlOl, R129, and
R133.
Check that the Front Panel Range and Function Switches
opera" properly. Also check that the appr"pr,ate frequency
was displayed upon power up. II the Front Panel Switchs
operate properly and the appropriate frequency was displayed
upon power up, then the Switch Input Section IS operating
properly. If the Front Panel Switches are not operating
properly or an inappropriate reading for frequency was
displayed upon power up, then check UlM, QlO2, RlOl, RI29
and Rl33~
5-12