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| Keithley 2400 SourceMeter review and teardown |
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| 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. |
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