Products > Test Equipment
Keithley 2400 SourceMeter review and teardown
kawal:
openloop
DAC U660 is back in - still runs hot - super hot
When set to 10V out the NVDAC pin shows -5.00V
DAC U661 is cold and output on pin NIDAC now remains 40mv no matter what current is set - so I killed something
I set ouptut to 10mA
With these conditions I get the following readings
OP AMP out -1.2V
TP213 -2.3V
TP212 0.36V
TP211 -1.67V
TP210 +7.8V
TP209 +12.7V
TP205 +12V
TP207 -0.44V
TP230 -13.9V
TP231 -0.83V
kawal:
--- Quote from: openloop on February 29, 2020, 06:03:55 pm ---
--- Quote ---Do you have a schematic of this unit ?
--- End quote ---
Nope, just bad experience. ;D
--- Quote ---TP207 = -7.4V
--- End quote ---
So the current control is bad...
Let's check the summing point where feedback is added to (current) DAC's output:
R238 pin 1: DAC
R238 pin 2: DAC + feedback
R238 pin 3: feedback
What are the voltages on those pins?
--- End quote ---
R238
pin 1 = -43mv
pin 2 = -0.833V
pin 3 = -0.833V
pin 4 = -0.833V
pin 5 = -43mV
openloop:
--- Quote ---TP213 -2.3V
TP211 -1.67V
TP207 -0.44V
--- End quote ---
That does not compute. Can you recheck those three? Value at TP207 seems wrong.
And while at it, check voltages at TP205, TP206, TP208
kawal:
--- Quote from: openloop on February 29, 2020, 07:18:29 pm ---
--- Quote ---TP213 -2.3V
TP211 -1.67V
TP207 -0.44V
--- End quote ---
That does not compute. Can you recheck those three? Value at TP207 seems wrong.
And while at it, check voltages at TP205, TP206, TP208
--- End quote ---
OK TP207 was wrong its +0.44V
Rechecked the Resistor network as well
R238
pin 1 = -43.3mV
pin 2 = -0.438V
pin 3 = -0.833V
pin 4 = -0.833V
pin 5 = -0.395V
pin 6 = +43.3mV
OP AMP out -1.2V
TP214 -2.3V
TP213 -0.4V (corrected)
TP212 +0.4V
TP211 -1.6V
TP210 +10.3V
TP209 +10.2V
TP205 +9.4V
TP207 +0.44V
TP230 -13.9V
TP231 -0.833V
While messing with the unit I set it to current mode and complacence voltage to 2.100V and the meter measured 2.10018V I checked the output and it was right no the money (2.10018V measure with Keithley 2700). The current was set to 10ma but the DAC must be dead as it always Measures 43mV on NIDAC . Current reading on the meter is 0.833mA and the output stage is not outputting any current at least based on the measurement across R562 R563 being 0.000mV
Tried it with Compliance Voltage of 21.0v and that works as well.
But current is always reading 0.833mA same as pins 2, 3 off R238. So the current feedback must be trying to correct for its reading.
U227 feeds directly to the pin IFB which I think is Current Feedback.
And this is the issues there is a large voltage on the indeed of this chip. The chip is a AMP03G which makes sense.
Now to figure out where this voltage difference is coming from there is a ton of switching going on in this area.
In voltage mode i get -240V all the time even when output is off. So something is working.
Updated firmware from version C11 to C32 while i was inside. Used images from Xdevs and TL866II plus programmer.
The memory was TMS28F020 and I saved C11 just in case.
So the measurement side is working and the output side is working .
NV dac still crazy hot probably needs to be changed - but outputting correct values.
openloop:
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 (FCOM), #4 and #7: 15V power, pin #6 output - in this situation it should be driven to its positive rail.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version