Products > Test Equipment
Keithley 2400 SourceMeter review and teardown
Jens01:
--- Quote from: Kjelt on May 15, 2019, 09:05:01 pm ---
--- Quote from: Jens01 on May 15, 2019, 05:53:41 pm ---Bought an defect 2400, bought as broken/for parts. Unit came from a automated test set-up so visually in good condition.
--- End quote ---
Troostwijk solar factory auction ? Missed those, the prices skyrocketed :(
--- End quote ---
No, Ebay. The name 'Keithley' was misspelled, so i was just lucky to be at the right time at the right place. ;)
kawal:
All,
I got a 2400 (199X vintage shipped with C06 firmware and currently running C11) with output of -240V with or without the output on. I have looked for ideas of what the issue could be on this forum but could not find the same exact issue replicated.
Reading the forum did help to get a general understanding of the possible issues. too bad there is no schematic for these available as it would make fixing these a lot easier.
So far what i have checked :
Output stage transistors - all good. Pulled the Bipolar Darlington power transistors to check.
Power supply 12V ok 5V oK +5VF, +15VF, -15VF, +30VF, -30VF all good
NIDAC, NVDAC signals adjust with output adjust.
EAMP is -7V which is maybe ok for the output of -240V ?
The board must be an early revision as the AD847 power supply clamping zener diodes are soldered direct to pins of the op amp and there is no room for them on the board.
The positive and negative supply of the AD847 was very low so i pulled it to check it.
Checked Q528, Q529 and 100 ohm resistors in the circuit to make sure these are good. ad they are.
With the AD847JN out it seems this might be the issue. While power consumption of the amp is normal (5.5ma) The amp will not work as a normal op amp. The output is not following the input and there is a 1.2V difference between the input + and input -. Maybe input stage is broken ( when setup at unity gain) To test i put the amp in a socket with bypass caps on socket. Amp configured in voltage follower mode with gain on +1. Supply was +/-10V and applied zero volts to positive input. Output was 1.2V and same difference on - Input pin.
Still not sure why the voltage was low on the power pins for the AD847. Waiting for replacement chip
openloop:
Have you checked output stage voltages?
They are separate from analog board sources (the ones you listed).
Output stage power comes through T500 transformer and two bridge rectifiers: CR500-CR503, CR504-CR507.
Their ground is at TP501
U500 (AD847) is bootstrapped so its power must be straddling positive output terminal. Thus, when talking about a voltage, you should mention to what "ground" it's relative to.
Additionally, while testing you probably can use any op-amp you've got - U500's pins 1,8 and 5(?) are not connected.
kawal:
Yes I did check the output stage voltages and they seems fine correct.
In regards to Op amp voltages I checked versus FCOM.
I am ready to put the output stage back in without driver amp. Without the driver the output should be putting out 0V since its a B class + H class hybrid.
I did find a little difference in the schematic and i will post here as it could help someone in the future. Basically the op amp should be working at +/-5.6V power supply and transients no bigger that +/-9V if the zener diods are right. Still waiting on proper amp but will try with AD845 with i got at local shop.
This is not the right amp as its a Jfet but should be ok for testing.
Ok Without Op Amp the output is 10V and 0V measured to FCOM which is strange with op amp its -240V so same as before .
Power is +/-250V and +/- 42V
Op amp power rails without op amp installed is +/- 5.6v
With op amp installed and -240 on output its +4.2V -2V to FCOM
Must be feedback loop issue ?
openloop:
--- Quote ---Without Op Amp the output is 10V and 0V measured to FCOM
--- End quote ---
FCOM is the positive output. So it's always 0V.
--- Quote ---With op amp installed and -240 on output its +4.2V -2V to FCOM
--- End quote ---
-2V is explainable: there are simply no more voltage headroom on the negative side when output is pulled all the way down.
+4.2v is suspect: it should be +5.5 or some such. It is set by VR500 6v zener and Q528 follower. That means that there might be not enough voltage at Q518 collector.
Just for clarity sake (when SMU's output is at -240v):
What are the voltages (FCOM relative) on all pins (2,3,4,6,7) of U500?
(I'm kind of confused by the way you listed them in different places)
What are the voltages on collectors and emitters of Q518, Q521?
Are any of transistors in the output stage warm/hot?
What is the voltage drop across R562? And R563 too? (just to see what kind of current we're dealing with)
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