(following on from the discussion of leaky DIP sockets) I could really do with an instrument which measures down at the picoamp level or lower. The Keithley 610C seems to be highly regarded around here, but they very rarely come up for sale here in the UK. Keithley's equivalent current model, the 6517B, is $8K, and from what I hear Keithley's build quality isn't what it once was... There is one used 610C on eBay, not working, in the US for about $100. Anybody have any experience of repairing these things? I found a sevice manual online, they don't look particularly difficult to work on, but I'm guessing one of the the most common faults is blown input transistors which are a matched pair on a module, only available from Keithley. Any advice? For $100 I'm tempted to take a gamble and have it delivered to our US office, one of our guys can bring it over next time he visits. OTOH if the parts are unobtainium I'll wait for a working one to appear. TIA
Keithley 610C repair
Started by ●December 1, 2015
Reply by ●December 1, 20152015-12-01
The switch and meter movement are pretty nice, so even if you can't get replacement MOSFETs, you could do a brain transplant with something like an LMC662 or 6001 and have a fairly swoopy gizmo. Cheers Phil Hobbs
Reply by ●December 1, 20152015-12-01
On 01/12/2015 14:05, Phil Hobbs wrote:> The switch and meter movement are pretty nice, so even if you can't get replacement MOSFETs, you could do a brain transplant with something like an LMC662 or 6001 and have a fairly swoopy gizmo. > > Cheers > > Phil Hobbs >If you search back postings in this NG a year or two ago John Larkin posted schematic and photos of a box he built around an LMC6001 which do pretty much the same job as the 610C for femto/pico ampere sleuthing. piglet
Reply by ●December 1, 20152015-12-01
On 12/01/2015 10:18 AM, piglet wrote:> On 01/12/2015 14:05, Phil Hobbs wrote: >> The switch and meter movement are pretty nice, so even if you can't >> get replacement MOSFETs, you could do a brain transplant with >> something like an LMC662 or 6001 and have a fairly swoopy gizmo. >> >> Cheers >> >> Phil Hobbs >> > > If you search back postings in this NG a year or two ago John Larkin > posted schematic and photos of a box he built around an LMC6001 which do > pretty much the same job as the 610C for femto/pico ampere sleuthing. > > piglet >I think it was the same discussion where I was talking about using a charge dispensing loop with a 100-pF Teflon cap to do the same sort of thing. It's easier without resistors. Voltage measurement is pretty easy--you can make a follower and measure its output with a normal DVM. I have a couple of dozen MOSFETs without gate protection, and you can still get 2N7002Es, some of which leak only a few electrons per second. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●December 1, 20152015-12-01
On Tuesday, December 1, 2015 at 10:17:47 AM UTC-5, piglet wrote:> On 01/12/2015 14:05, Phil Hobbs wrote: > > The switch and meter movement are pretty nice, so even if you can't get replacement MOSFETs, you could do a brain transplant with something like an LMC662 or 6001 and have a fairly swoopy gizmo. > > > > Cheers > > > > Phil Hobbs > > > > If you search back postings in this NG a year or two ago John Larkin > posted schematic and photos of a box he built around an LMC6001 which do > pretty much the same job as the 610C for femto/pico ampere sleuthing. > > pigletYeah I might think about building my own too. I've measured pA with a "leaky" Fet opamp. The LMC662 looks nice also (as Phil noted.) And it's a lot cheaper... you could blow up a few for ~$1.5 each. George H.
Reply by ●December 1, 20152015-12-01
On Tue, 01 Dec 2015 15:18:02 +0000, piglet <erichpwagner@hotmail.com> wrote:>On 01/12/2015 14:05, Phil Hobbs wrote: >> The switch and meter movement are pretty nice, so even if you can't get replacement MOSFETs, you could do a brain transplant with something like an LMC662 or 6001 and have a fairly swoopy gizmo. >> >> Cheers >> >> Phil Hobbs >> > >If you search back postings in this NG a year or two ago John Larkin >posted schematic and photos of a box he built around an LMC6001 which do >pretty much the same job as the 610C for femto/pico ampere sleuthing. > >pigletThe Keithley is a fabulous instrument, light-years better than the thing I built. I'd buy the dead one and try to fix it. It might be something easy like the power supply, and even if the input fets are blown, that can be fixed. I see four 610s for sale on ebay at this instant. Used equipment brokers often have them, too, and those can be bought guaranteed working.
Reply by ●December 1, 20152015-12-01
On Tue, 1 Dec 2015 10:22:23 -0000, RBlack <news@rblack01.plus.com> wrote:>Any advice? For $100 I'm tempted to take a gamble and have it delivered >to our US office, one of our guys can bring it over next time he visits. >OTOH if the parts are unobtainium I'll wait for a working one to appear.At $100, there's almost certainly something wrong with it. Still, methinks it's worth trying to fix it. 610c manual at: <http://122.physics.ucdavis.edu/course/cosmology/sites/default/files/files/Ferro%20Electricity/Keithley610manual.pdf> The schematic is dated 1968 so I would suspect that the big electrolytics in the power supply have dried out. If that doesn't do the trick and it looks like the two input FETs are fried, carefully remove them (using static protection) and replace them with whatever you can find that's close, just to see if it works. If it works, but leaks badly on the higher sensitivity scales, try to find suitable substitute FETs. The manual does not list a replacement part number for the input FETs, which are designated as part of the input PCB, Keithley 23733A. However, the photo looks like they're easily replaced: <http://holzleitner.com/el/keithley-610c-electrometer/keithley-610c-input-section.jpg> Note the black Fairchild xsistors above the FETs. They're epoxy filled and might be IR light sensitive. Internal detail and photos: <http://holzleitner.com/el/keithley-610c-electrometer/index-en.html> Calibration costs about $250 to $300 which might make it more attractive to buy something that works and is calibrated. Interesting readings and photos: <http://www.eevblog.com/forum/projects/electrometer-input-stage/> -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Reply by ●December 1, 20152015-12-01
On Tuesday, December 1, 2015 at 2:22:27 AM UTC-8, RBlack wrote:> (following on from the discussion of leaky DIP sockets) > > I could really do with an instrument which measures down at the picoamp > level or lower. The Keithley 610C seems to be highly regarded...> There is one used 610C on eBay, not working, in the US for about $100.> I'm guessing one of the the most common faults is blown input > transistors which are a matched pair on a module, only available from > Keithley.You can get CD4007UB with several pairs of MOSFETs, for very cheap and experiment doing the replacement. Or, ALD sells well-matched pairs, PMOS or NMOS... <http://www.mouser.com/catalog/catalogusd/645/2382.pdf> There's some bootstrapping in the Keithley input circuit, so the replacement's leakage will be far below the 'tested' leakage-under-bias spec.
Reply by ●December 3, 20152015-12-03
Phil Hobbs wrote:> On 12/01/2015 10:18 AM, piglet wrote: >> On 01/12/2015 14:05, Phil Hobbs wrote: >>> The switch and meter movement are pretty nice, so even if you can't >>> get replacement MOSFETs, you could do a brain transplant with >>> something like an LMC662 or 6001 and have a fairly swoopy gizmo. >>> >>> Cheers >>> >>> Phil Hobbs >>> >> >> If you search back postings in this NG a year or two ago John Larkin >> posted schematic and photos of a box he built around an LMC6001 which do >> pretty much the same job as the 610C for femto/pico ampere sleuthing. >> >> piglet >> > > I think it was the same discussion where I was talking about using a > charge dispensing loop with a 100-pF Teflon cap to do the same sort of > thing. It's easier without resistors. > > Voltage measurement is pretty easy--you can make a follower and measure > its output with a normal DVM. > > I have a couple of dozen MOSFETs without gate protection, and you can > still get 2N7002Es, some of which leak only a few electrons per second. > > Cheers > > Phil Hobbs >...which brings up a question: can one count the electrons (like Millikan oil drop bit)?
Reply by ●December 3, 20152015-12-03
On 12/03/2015 01:42 AM, Robert Baer wrote:> Phil Hobbs wrote: >> On 12/01/2015 10:18 AM, piglet wrote: >>> On 01/12/2015 14:05, Phil Hobbs wrote: >>>> The switch and meter movement are pretty nice, so even if you can't >>>> get replacement MOSFETs, you could do a brain transplant with >>>> something like an LMC662 or 6001 and have a fairly swoopy gizmo. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>>> >>> >>> If you search back postings in this NG a year or two ago John Larkin >>> posted schematic and photos of a box he built around an LMC6001 which do >>> pretty much the same job as the 610C for femto/pico ampere sleuthing. >>> >>> piglet >>> >> >> I think it was the same discussion where I was talking about using a >> charge dispensing loop with a 100-pF Teflon cap to do the same sort of >> thing. It's easier without resistors. >> >> Voltage measurement is pretty easy--you can make a follower and measure >> its output with a normal DVM. >> >> I have a couple of dozen MOSFETs without gate protection, and you can >> still get 2N7002Es, some of which leak only a few electrons per second. >> >> Cheers >> >> Phil Hobbs >> > ...which brings up a question: can one count the electrons (like > Millikan oil drop bit)? >Hard to do at room temperature, especially in a relatively large device like that. You can do it in small devices at low temperature. (Google "coulomb blockade".) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
