Another sick Keithley 2000 - Page 1
Forum section: electronics / repair

author: jchw4
author_rank: Regular Contributor
timestamp: March 08, 2021, 09:22:23 am
content: Some time ago I got mechanically damaged k2000, which otherwise was perfect. It still reads 5.00000 V from my DMMCheck.(k2000 reports last calibrated in 2002)But yesterday I noticed that it's 1M range is broken both in 2W and 4W.For example, 100k in 2W mode:Code:100k range: 100.7717k1M range: Overflow10M range: 00.10071M100M range: 000.1007MShorts:Code:100k range: 000.0003k1M range: -0.000006M10M range: 00.00003M4W:Code:1.80 Ohm on 1M : -0.000053 M2.78 Ohm on 1M : -0.000072 M11.8 Ohm on 1M : -0.000672 M101.8 Ohm on 1M : -0.002190 M1.000 k on 1M : -0.021508 M9.967 k on 1M : -0.214120 M100 k on 1M : Overflow(values on the left measured using other ranges)All tests pass.Current source is perfect (measured with external meter).TP104 seems to be correct.What could it be? I have a feeeling that it's calibration memory.Herehttps://www.eevblog.com/forum/repair/first-time-on-keithley-2000/msg974309/#msg974309another user shared calibration dump commands and their actual values.Here are mine:Code:000000000262145000000000393216000000000196608000000000262144+2.74088039E-02+2.74717795E-01+2.74241546E-02+2.74939096E-01+7.83504339E-05+2.74746629E-02+2.75300742E-01+8.12454578E-05+2.74820894E-02+2.75495528E-01+2.74714668E-02+1.92738696E-01+7.83581243E-05+2.73505044E-02+2.74136247E-01+1.37793306E-02+2.76778882E-01+9.98209300E-01+9.52346951E-01+1.00000000E+03+9.99984500E+02+1.00000500E+01-1.00000700E+01+1.00001400E+02+1.00000000E+03+1.00000000E+04+1.00000000E+05+1.00000000E+06+1.00000000E-02+1.00000000E-01+1.00000000E+00+1.99251556E-06+1.88449784E-06-6.65748151E-07+1.41637118E+00-1.41637561E+00+1.41689936E-01-1.44000000E-01+2.48186119E-05+1.72858864E-05+5.29676357E-06+3.29774682E-06+3.18277699E-06+9.17269493E-02+9.99929726E-01-1.93286724E-06-2.00583545E-06-1.94541648E-06-1.97593550E-06+1.17605155E-06+1.41526718E-01+1.42849062E-01+1.42880911E-01-6.65767966E-02+9.17000000E-02+1.19220998E-06+1.18602474E-06+1.43014682E-02+1.41262068E-03+1.41139930E-02Comparing them I can see that one value is significantly different:Code:300.000%-0.537%-0.261%-0.712%-0.403%-80.024%-0.480%-0.216%-79.150%-0.664%-0.360%-0.586%-0.288%-80.008%-1.071%-0.791%-1.431%-0.824%-0.179%-4.247%0.000%-0.002%0.000%0.001%0.001%0.001%0.000%0.001%0.003%0.000%0.000%0.000%78.899%130.010%-4495.288% (-6.65748151E-07 +1.51468621E-08 1111111111111111111111111111111110110101001100101011010111011101 110010100000100001110001001101)-0.235%-0.235%-0.238%0.000%61.263%41.971%113.748%186.489%193.640%0.090%0.007%-24.512%-17.552%-23.834%-22.502%-2.625%-0.058%-0.016%0.001%-104.660%0.000%104.454%96.454%-0.322%-0.692%-0.737%(I am not sure that interpreting these values as float32 is correct, but it looks reasonable to me.)So my value is -6.65748151E-07 while other users value is +1.51468621E-08 .Could it be cal EEPROM fault?What else should I check?

author: Kleinstein
author_rank: Super Contributor
timestamp: March 08, 2021, 09:41:54 am
content: A negative Ohms readings may be a faulty cal constant. The value seem to be off by a factor -21.A first point to test would be to measure the test current the meter uses for the tests with a 2nd working meter.Another possible test would be to measure the "2 wire resistance" of a 1.5 V battery in the 2 M range. This should show how the measured voltage is converted to the result.

author: jchw4
author_rank: Regular Contributor
timestamp: March 08, 2021, 10:27:52 am
content: Quote from: Kleinstein on March 08, 2021, 09:41:54 am121GW displays 10uA in 100k and 1M ranges, and 0.7uA in 100M range. It matches k2000 specs.Quote from: Kleinstein on March 08, 2021, 09:41:54 amMeasuring Ohms of 1.00000V source (Ronan X85 calibrator that I posted):Code:10MOhm: 1.63400 M1MOhm: Overflow100k: 99.1294 KIncreasing voltage actually makes ohms read more negative. -1.000098 MOhm matches 0.470060V on the input.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 08, 2021, 10:34:35 am
content: This really looks like a bad calibration constant. AFAIK the Keithley meters allow to calibrate individual ranges. So one may be able to get at least a somewhat working state back with cal ran for the 2M range.

author: jchw4
author_rank: Regular Contributor
timestamp: March 08, 2021, 11:40:27 am
content: Quote from: Kleinstein on March 08, 2021, 10:34:35 amAnd I guess that EEPROM needs to be replaced ASAP.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 08, 2021, 01:53:51 pm
content: It is not sure that this is really a damage to eeprom. It could as well be just a soft error, that would be corrected with new written values.Damaged EEPROMs are relatively rare.The wrong values could be by an unintended call of a memory write - possibly by the former owner, or a general computer problem like a brown out. In this case even check sums would not help.Ideally I would expect quite some error correction / checksums, so that corrupted cal data would be rate. The memory chip should have several times the capacity to allow redundant storrage.At least a good check sum should be there to give a warning.With computers ideal and real implementation are 2 things.