| Products > Test Equipment |
| Keithley 2400 SourceMeter review and teardown |
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| openloop:
--- Quote ---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 --- End quote --- OK, it's starting to make sense... -0.76V and -0.4V at TP213 are both bad. TP213 is the output of control inputs mixer. TP205 (voltage POS), TP206 (voltage NEG), TP207 (current POS), TP208(current NEG) are respective control inputs to that summing thing. What are the voltages on TP205, TP206, TP207, TP208 (in voltage mode) |
| kawal:
TP205 9.4V TP206 4.4V TP207 -3.8V TP208 -3.8V Setting is volts 10.0000V and compileance current is set to 1.05000mA . Reading Amps +0.75753mA. in lower ranges the meter shows overflow for current. Reading volts Overflow on Tp231 is -7.59V Tp230 is +13.9V Pin 2 of U227 +3V Pin 3 of U227 -4.5V Pin 6 of U227 =TP231=-7.59V (measures 0 ohms between these btw.) |
| openloop:
--- Quote ---TP205 9.4V TP206 4.4V TP207 -3.8V TP208 -3.8V --- End quote --- Assuming these values are correct. ;) And in voltage mode, right? Those readings imply that control signal (and output that follows it) is dragged down by the driver that controls current (negative voltages at TP207 and TP208). Surprisingly enough. (unless you mixed up polarity again, then the goose chase will continue) Just to make sure, What are the voltages at TP209, TP210,TP211 and TP212? (these are outputs of buffers for TP205, TP206, TP207, TP208 respectively. Take measurements in the same mode that you had when you've got readings above (so I'm not comparing apples to oranges). See how many test points they've put in this area? The place is trouble. |
| kawal:
Openloop I am grateful for the help. and looking at the points you recommended definitely is making this thing more understandable. The troubleshooting will need to wait as I have a business trip starting today. Will be back to it in 2 weeks. I think thats why I was rushing it and damaged the dacs (I think i did as they measured good before.) Both dacs are running burning hot which I think it is not normal. I will be back in 2 weeks to continue this story. Thanks again for your help I need to figure out the current measurement section as next priority, That side is definitely sick,. |
| kawal:
A user made me aware that there could be a massive failure of the current sense resistor switching circuit. The output would in that case show current as there are back to back protection zener diodes across the current sense section. So if none of the resistor sections are on, there would be a about 5V drop across the Current sense Low and Current Sens Hi . This seems to be what I am experiencing. This would be every bad. :( |
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