Keithley 2400 help - wrong button - goes dead - Page 1
Forum section: electronics / repair

author: elee
author_rank: Newbie
timestamp: November 30, 2023, 12:36:48 am
content: While connecting the Keithley directly to an 5 1/2 Owon multimeter on auto range to compare precision - i did some stupid things that i regret...Keithley was sourcing voltage, around 5V and all was good. While playing with the other buttons on the Keithley, i clicked Measure voltage, measure current - and at the end pressed the "source current" while being still live voltage source (lamp was on) -> afterwards was short click and whole device went silent. No screen, no sign of life.As far as i remember the previous setting for the current source was in nA range..- I always believed the Keithley 2400 has short circuit protection, or im fundamentally wrong?- The fuse on the cord plug is good. Is there any other place to check for fuses?- Can some of the Keithley veterans point to me where to start looking, and maybe share theory what could have happened?Thank you!!!

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: November 30, 2023, 03:41:50 am
content: You probably cooked off a trace somewhere. I don't see many images of the internals inside, but from what I can see, the traces that connect to the input receptacles seem to be thin so hopefully they acted as a fuse and the failure didn't fry everything.I also don't see any fuse anywhere for the current range.Please include images of the internal guts. There's likely soot everywhere, don't clean off the soot yet, take a good image of the two PCBs on two sides, and then you can start cleaning off the soot.The soot locations would help locate what components released the magic smoke.Edit: This website has many images of the internals:https://xdevs.com/fix/kei2400/

author: ArdWar
author_rank: Frequent Contributor
timestamp: November 30, 2023, 06:12:06 am
content: SMU are supposed to be self limiting/self protecting, hence the apparent lack of protection on theoutput. It shouldn't be able to kill itself, as long as you don't backdrive it.There's "service manual" in Tek's website (orhttps://xdevs.com/doc/Keithley/2400/2400_902_01D.pdf). For a start just follow the testpoint checklist in pp.10-4/10-5. Beware of the 200V supply!That there's "no sign of life" is kinda concerning tbf. Hope its's just the digital board, or digital board's supply that gave up.

author: alm
author_rank: Super Contributor
timestamp: November 30, 2023, 10:25:40 am
content: Quote from: elee on November 30, 2023, 12:36:48 amThis was not a short circuit, however. It was set to source current (e.g. adjust the output voltage until the output current reaches the set point), and possibly got fed a voltage well outside its set compliance range (you don't specify the compliance voltage range or the voltage it was fed). Check the theory of operations in the service manual with the rough schematic of the output stage. If it was a high voltage my guess is that some of the output FETs got blown, and possibly the circuit driving their gates. That wouldn't cause the unit not to turn on, so it's possible that the external voltage got on the +/- 36V rails and killed something in the power supply.I don't really see how this could cause just the digital circuit to fail unless it's just a random failure.

author: openloop
author_rank: Regular Contributor
timestamp: December 01, 2023, 12:54:44 am
content: Thou Shalt test voltages.Service manual has the diagram of how the whole thing is powered. Start there.