Electronics > Repair

Keithley 225 current source: -136V output voltage

(1/1)

fedora_88:
Hello,
yesterday I recognized that my Keithley 225 current source shows about -136V output voltage at the output under the following conditions:

- polarity: +
- compliance voltage: 10V (it doesn't matter if it is 10V or 100V position)
- filter: on or off doesn't matter
- 100mA range
- all current-knobs in zero position (00,0mA)
- no load on the output, only a 10MOhm Multimeter in voltage mode

When I short the output with a second multimeter, the flowing current is only -10uA. When I open the short again the voltage slowly rises until -136V. When I set current to 1mA or 10mA the voltage rises to the selected compliance voltage (+10V).

Beside of that it works perfectly normal. So I don't know if there is an error, or if that behavior is normal. So to all Keithley 225 owners, can you please check if your device shows the same issue.

kind regards
Thomas

Vgkid:
Have you tried measuring it across a load.

jlmoon:

--- Quote from: fedora_88 on October 21, 2014, 05:40:51 pm ---Hello,
yesterday I recognized that my Keithley 225 current source shows about -136V output voltage at the output under the following conditions:

- polarity: +
- compliance voltage: 10V (it doesn't matter if it is 10V or 100V position)
- filter: on or off doesn't matter
- 100mA range
- all current-knobs in zero position (00,0mA)
- no load on the output, only a 10MOhm Multimeter in voltage mode

When I short the output with a second multimeter, the flowing current is only -10uA. When I open the short again the voltage slowly rises until -136V. When I set current to 1mA or 10mA the voltage rises to the selected compliance voltage (+10V).

Beside of that it works perfectly normal. So I don't know if there is an error, or if that behavior is normal. So to all Keithley 225 owners, can you please check if your device shows the same issue.

kind regards
Thomas

--- End quote ---

Thomas,

I suspect  you have a problem with the differential amplifier section (drive amplifier)  I have fixed a few of the calibrators similar to this one, check the current limiting resistors that are at the top and bottom power supply rails.   These resistors are what feed the supply to the bipolar differential amplifier to establish a balanced supply.  Best of luck!


JLM

Navigation

[0] Message Index