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Keithley 2400 SourceMeter review and teardown

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kawal:

--- Quote from: openloop on March 01, 2020, 01:28:57 pm ---You provided different values for TP213. It was both -2.3V and +0.4V
Did you mix-up TP214 and 213?
TP213 cannot be -2.3V - it's clamped.
Man, focus!

+0.4V at TP213 is good so control input is correct - it tries to pull the output up.

If TP214 is indeed -2.3V then the suspicion lands on U236 (and its neighborhood) which is the last buffer between TP213 and TP214.
Check voltages on its pins.
pin #3 must be the same as TP213, pin #2 should be at floating ground, #4 and #7: 15V power, pin #6 output - in this situation it should be driven to its positive rail.

--- End quote ---

Yes got TP213 mixed up at the very start adn continued to name it incorrectly.  TP214 is EAMP and that is -2.3V in voltage mode but it is absolutely fine in current mode (around 0V).
Pretty sure the issue is not U236 as it works as should in current mode
Either way DACs are hot and current  dac is dead along with the current sense loop showing something that is not there.
I think at the end i need to figure out the current sense loop around the resistors at the input and the switching of these resistors. There is a voltage imbalance there.

openloop:
 |O

So what's on TP213 in voltage mode?

kawal:
TP213 -0.4V.....-0.76V  (must have switched leads at some point as it seems to always negative)


OK  in Voltage mode :
   TP213 in voltage mode is -0.76V  in lower current ranges and -0.4V in higher current ranges
   TP214 is -2.3V
In Current mode
TP213 440uV
TP214 70uV


openloop:

--- Quote ---TP213 +0.4V
--- End quote ---
And TP214 is still -2.3V?

Then check voltages on U236 as I asked before. Something is wrong there.

kawal:

--- Quote from: openloop on March 01, 2020, 02:11:11 pm ---
--- Quote ---TP213 +0.4V
--- End quote ---
And TP214 is still -2.3V?

Then check voltages on U236 as I asked before. Something is wrong there.

--- End quote ---

U236 in voltage mode

pin 2 0V
pin 3 -0.4V (depends on current ranage)
Pin 6 -13V (output i guess)
pin 4 -15V
pin 7 +15V


U236 in current mode
 pin 2 0V
pin 3  uVs
Pin 6 -2.3 (output i guess)
pin 4 -15V
pin 7 +15V

In Voltage mode the unit is trying to limit the output as the current its reading is wrong. So based on the data the analog section must correct the situation and the result -240V on output.
In current mode the current measured by the unit  is below the settings  ( I give it a 1mA setting )  and the meter shows less than that with output open.
In current mode the output reaches compliance voltage settings.   I can change the compliance voltage setting and the output follows the setting exactly. 

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