Keithley 2000 TF-245 version / year question  - Page 1
Forum section: electronics / repair

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 12, 2024, 07:55:44 am
content: HelloFollowing a doc locate on this forum ( see linked pic ) there is several version of the TF-245My question : does there is equivalent , different design but pin to pin alternative ?I plan to make a patch base on 0603 componentRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: May 12, 2024, 09:32:22 am
content: I don't think the diagram of the A version makes much sense. it could be more like showing the measured resistance, not counting indirect paths.The verion B should be the right one.The resistor array should be rather stable. So a circuit from separate 0603 size resistors could be tricky. A final solution may want at least some resistor arrays for parts of the job.One may not have to replace the whole array. There are different sections:1) ref. amplification can get the auxiliary 13.3 V for the ohm part.2) an auxiliary voltage for pin 14 for the fine slope of the ADC (not that critical)3) the 3 resistors ~ 30 K for the integrator input (could likely be 3 equal values)4) the gain part (1K+9K+90K)

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 12, 2024, 12:38:04 pm
content: HelloDear KleinsteinThanksThanks I work on a patch base on a modified SAMTEC header and a PCB on the top to allow 0603 resistor , I can solder easily 0603 perhaps 0402Just make a mock-up right now , TF-245 is real source of problem and as 2000 / 2700 and other Keithley are now quite old that avaibility problemRegardsOS

author: coromonadalix
author_rank: Super Contributor
timestamp: May 12, 2024, 12:43:08 pm
content: other thread who talk about ithttps://www.eevblog.com/forum/repair/keithley-tf-245-replacement-options-(k2000-models)/

author: marcumr
author_rank: Contributor
timestamp: May 12, 2024, 05:21:56 pm
content: HELLO.Some time ago one could order from Keithley-Tektronix (U.S.A.)the famous and sought-after TF-245. I never managed it.

author: picburner
author_rank: Frequent Contributor
timestamp: May 12, 2024, 05:49:00 pm
content: Some time ago I wrote directly to Tektronix to have some spare parts including some TF-245.They told me they didn't sell to private individuals and directed meherewhere they got everything for me.This at least for buyers in Italy.

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 12, 2024, 08:03:19 pm
content: HelloKeithley have been purchased by Tektronix , my last call 4 years ago regarding my 2182 was more than disappointing ..... but Tektronic France have a long story of:-Another concern is the cost regarding the value I try to keep them alive at affordable cost , only parts located in the net are at 113 USD per unit without warrantyI have mostly complete the mock-up with the 0603 resistor I will try the week to check mecahnical fitting if that fit and select the best 0603 resistor I can locateRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: May 12, 2024, 08:26:30 pm
content: It would be tricky to get good performance from individual resistors. Resistor arrays (e.g. MORN series) can get quite good matching, especially with intermediate resistor values. If one would not mind a slightly higher supply current, one could separate the ohms part (the 13.3 V - should be less critical) and the reference amplification. This way 4 x 10 K could be used instead of the (1K+9K) + 10 K +20 K.The 30 K are not standard values, so maybe as 10K+20K or an array with 10 x 10 K.The amplifier gain (1K+9K+90K) could use a resistor array (VTF330).At the very lest one could use ACAS resistor arrays, which are the same size as 4 x 0603.

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 13, 2024, 06:58:48 am
content: Quote from: Kleinstein on May 12, 2024, 08:26:30 pmHelloThanks for the advice regarding resistor net I check this solution this weekThat very sad to not see a robust design in the Keithley serie 2000 with a small SOIC resistor net rather to use through the hole type as the Caddock ceramic , and worth as there is Caddock resistor on the PCB for other purposeI can stack two pcb on the SAMTEC header pin I link a first CAD design with 0603 , done to check the mechanical fitting onlyRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: May 13, 2024, 07:37:10 am
content: The Cadock ceramic networks that are used for high voltage dividers are usually thick film and thus not super stable. They are special to withstand high voltages, but for low voltage more normal thin film types would be preferable.Chances are there would be more space available, possibly a vertical mounted PCB.

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 13, 2024, 08:19:25 am
content: Quote from: Kleinstein on May 13, 2024, 07:37:10 amHelloI agree , my remark was more on the size room on the board compare to the soic 16 broadI check the vertical solution PCB , my first concern is to limit as possible force on the SOIC solder tabQuestion :As the Keithley board have a stiif aluminium hood with a 4 mm pillar on the front , Do you think that could be possible to extend this hood as a PCB support and link the SOIC foot print with wires ? The aim will be to avoid mechanical stress on the small SOIC solder tab and also allow to install real resistors net without room limitation.RegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: May 13, 2024, 09:29:36 am
content: The mechanical stress could be indeed limiting. It should still be OK for normal use, but shipping it (e.g. for calibration) could become an issue.Using wires and an edditional external PCB could work, though it adds a little copper resistance. The ref. amplification for some reason uses a rather fast amplifier but should be OK with the relatively large capacitors.Still the extra capacitance is not great - so the cable should not be long.

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 13, 2024, 10:56:11 am
content: Quote from: Kleinstein on May 13, 2024, 09:29:36 amHelloCould be possible to install a plate like the white page on the pictureWiring will be less that 40 mm long as the resistor PCB will be on the top of the 245 foot printIf other people are interested I can laser cut some and propose kits after final design testingRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: May 13, 2024, 12:14:22 pm
content: The screws close to the rear side are likely not suitable, as they would be at or near the ground / outputside potential. The hood screw position does not look that bad. 60-100 mm of cable would likely be acceptable from the capacitance. For holding the PCB could likely extend to the screw area. The first point is seeing if the meter is working at all with modified resistors.

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 13, 2024, 01:54:18 pm
content: Quote from: Kleinstein on May 13, 2024, 12:14:22 pmHelloI agreeAs my 2000 ( this one ) is dead right now and I have also a 2700 with problems , I can built a prototype and test various circuits / components to see to result . accurate resistor are easy to locate when they are bigger too , Vishay foil as exampleI will post progressMouser have 0603 and 0805 in 0.05% 10ppm SMD that quite cheap as under 1 Euro per unit and enough to make first testRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: May 13, 2024, 04:44:05 pm
content: There is no need to go for low tolerances - there is essentially no gain from this. The meter should tolerate quite some deviation from nominal. Even with 0.05% resistors one would still need recalibration as the gain with change a little. Some compensation is possible by changing R300 if needed.The point is more with matching between the three ~ 30 K resistors towards the integrator and the chain with 20K 10K 9K1K from pin 1 to 3. Here it could make sense to use 4 x 10 K as a set with 100 K in parallel to 10 K to get close to 9 K. ORN / MORN resistor arrays are not that expensive (~ 4 EUR) and usually good matching (e.g. 1 ppm/K range for 10 K). ACAS would be small and cheap.Even with seprate resistors it can make sense to have at least the 20 K as 2x10K.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 13, 2024, 05:04:07 pm
content: would a tf-245 equivalent feasible, is there some companies who can do custom value / part / like this onewill we scrap meters because of this %@ of part ? that's why i never bought theses series of meters because of that single part ....i do hope some substitution will be feasible

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 13, 2024, 06:35:48 pm
content: Quote from: Kleinstein on May 13, 2024, 04:44:05 pmHelloThanks for advises , I will check and sort the resistor I have a kelvin setup for SMD and I can try to adapt a jig for null meter in the aim to control SMDQuestion :ppm/C for resistor from the same batch are normally the same OR I need to to make measurement at several temperatures ? my kelvin jig is in controlled temperature enclosureSetup of resistor :as on the ''top plate roof'' there is room to place a 32 mm x 80 mm PCB I can use several setup without real problem I can even set a small thermal insulation box and why not an oven if necessaryRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: May 13, 2024, 07:49:57 pm
content: There is no real need to go over the top with the resistors. After all it is only a 6 digit meter.With resistor from the same batch one often gets some matching, but of cause not perfect and not guaranteed. Things can also be different between types.There should be no need for super accurate resistor value matching - if at all it would be TC matching and getting comparable long time drift / PCB stress effects.For the self heating effect (especially the 30 K at the ADC input) the tight thermal coupling in an array would be an additional advantage over separate resistors.Still 30 K as an array are a bit tricky (3x10 K or 10 K +20 K).It is a bit clear if the resistors for the references should be exactly equal or a slight difference (e.g. on the order of 1/128) wanted - whicht way fits depends on how the result is calculated. So an extra series resistor (e.g. ~ 234 ohm) for pin 11 may make sense to have the option to adjust.

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 14, 2024, 06:04:41 am
content: Quote from: Kleinstein on May 13, 2024, 07:49:57 pmHelloOk I make a trial and post the results step by stepRegardsOS

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 14, 2024, 06:07:59 am
content: Quote from: coromonadalix on May 13, 2024, 05:04:07 pmHelloI am in process to tryEven as used a 2000 and some other Keithley cost $$$$ and use the 245 component and that sad or stupid to be force to scrap 600 USD or more measuring instruments IF there is a robust solution to repairRegardsOS

author: voltsandjolts
author_rank: Unknown
timestamp: May 14, 2024, 06:51:23 am
content: Quote from: coromonadalix on May 13, 2024, 05:04:07 pmYou have the option to buy a newer version that doesn't have the TF245, uses off-the-shelf arrays instead.

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 14, 2024, 08:39:16 am
content: Quote from: voltsandjolts on May 14, 2024, 06:51:23 amHelloYes but there is a lot of old models still in use and or need repair so rather to put them in the trask bin , I try to repair / upgradeTake in consideration that other Keithley use also the 245 component not only the K2000 as the 2306 have the two TF-245 and 2010 alsoIn the 2010the fact to use a bespoke connector with the 245 SMD foot print allow to install the patch on mostly all 2000 serie KeithleyRegardsOS

author: coromonadalix
author_rank: Super Contributor
timestamp: May 14, 2024, 04:09:51 pm
content: that's what i want to seeOP have you seen theses ?? Dip to SOIC adaptershttps://www.epboard.com/eproducts/protoadapter3.htm#DIP-16%20to%20SOIC-16%20WIDE%20IC%20Adapter

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 14, 2024, 06:05:52 pm
content: Quote from: coromonadalix on May 14, 2024, 04:09:51 pmHelloThanks , interestingI have located that a SOIC header on which I can fit a socket to link my patch PCB by wire as I search / prefer to avoid stress on the main PCB but also be able to manage temperature / pcb stress of my in process patchI link the ''quick and dirty first aluminium plate base on the CAD I have cut this day , patch pcb will not fit directly on this plate but on a SS304 plate with O ring to limit stress and dilatation effect7 mm Holes net have been added to avoid to trap the heat of the microcontrollerRegardsOS

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 15, 2024, 02:50:19 pm
content: HelloUpdate , this Harwin connector ( header ) can be soldered in place of the 245 componentRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: May 15, 2024, 03:49:59 pm
content: With the resistor values I don't know if one needs rather accurate ratios at some places. It depends on the software inside the meter, if the use some kind of norminal values for the slow ration or do an extra measurement (e.g. special factory calibration or in between normal measurements). Ideally one wants an option to trim 2 of the resistors, to adjust the ratio of the positive , negetive and small slope.

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 18, 2024, 04:32:16 pm
content: Quote from: Kleinstein on May 15, 2024, 03:49:59 pmHelloI have draw two PCB base on 0603 resistor ( 1K and 10 K in serie for most of them ) and header i Have checked the stack height I continue to work on the header connector BOMI can sort / measure the 0603 on my Kelvin 4 wires test jigI link some screen printsAs I have some room on the PCB I can add additional 0603 for trimming , my first goal is to test a solution asap , after I can re design PCB with resistor net if necessary , 0603 are easily available from MouserRegardsOS

author: Overspeed
author_rank: Frequent Contributor
timestamp: May 22, 2024, 07:28:52 pm
content: Helloa question for KleinsteinOn Xdev website there is a table value of the 245 resistances27.5 K looks to be closer than 27.4 than 27.5Note : thanks to Xdev for his amazing workRegardsOS