Keithley 2000

[EMUD]

Hi,
a view over all the values seemed to give the following information:

1. R271 (TF-245) is a thin film coustom resistor network with 0.1% or better tolerance.
2. The values given in the reversed schematic are meeting the measured TF-245 s.
3. For some resistors (i.e. the 1K,9K and 90K) the pecise value is not the problem,but the ratio.
4. For some resistors the value has to be precise, i.e. the charging Rs for the integrator.

OK,
now it should be no problem to check the own TF-245.

Thanks

EMUD

[EMUD]

Hello,
the new TF-245 has arrived. Since I have got 4 arrays I have checked the values.

R1          R2          R3           R4          R5           R6         R7         R8          R9         R10        R11

0.9999K  8.9999K 10.0001K 20.000K  14.9995K 30.173K 29.708K 30.178K 27.421K 1.0003K 9.0040K

1.0002K  8.9989K   9.9985K 20.000K  15.0035K 30.168K 29.697K 30.166K 27.415K 1.0000K 8,9990K

1.0002K  8.9999K   9.9995K 19.996K  14.9973K 30.173K 29.700K 30.176K 27.416K 1.0001K 8.9993K

0.9997K  8.9960K 10.0030K 19.990K  15.0012K 30.176K 29.704K 30.174K 27.417K 1.0006K 9.0007K


R12

90.001K

89.979K

89.982K

89.990K

I have replaced my faulty TF-245 and all the problems are gone.

But I have discovered a strange behaviour with the self test:

Software A02

When selecting ACV or FREQ and starting selftest, all tests failed! Starting self test after starting the unit there is no problem with the selftest !!

Has anyone seen this, too ?

Best regards and a nice easter weekend

EMUD

[EEVblog]

Test

[miguelvp]

somewhere in page two of this thread something went really wrong, I just get a blank page and the only way to read it is by pressing reply and read the messages bellow

[picburner]

To the Administrator:
can you repair the page 2 of this thread?
It has become invisible, thanks.

[Robert]

Hello Everybody,

Sorry for resurrecting this quiet old topic.

I have a Keithley 2000-20 with quiet strange behaviour.
Most times it works normal but I don't have another 6.5 digit DMM (or better) to check accurecy of the last digits, so it could be slightly off.

Sometimes it is measuring complete bullshit and selftest 101.2 and following will also fail than. This is absolute random and sometimes it fixes itself, somtimes after powering on and off or switching ranges.
I already replaced the relais (and the tweeter by the way) but this haven't made any difference.

After several weeks of short trubelshooting sessions (the error is wenting away when you hunt it) I'm pretty sure that my TF-245 is gone.
The 27.42K resistor between pin 10 and 12 goes open when I heat it up.
I can measure it in circuit when powered off (Q127 and Q131 are non conducting by default). In non failure state the value is 27.468K (in circuit) not bang on but close. When I heat it up the resistance rises slowly until it suddely changes to infinite. This corresponds to the voltage measured on pin 10 when stopping after test 101.2, if it passes, I can measure 6.507 V as result of the voltage divider of R300 and the resistor inside the TF-245. When the tests 101.2 fails the voltage of pin 10 is at 7.015 V, exactly the reference voltage which indicates that no current flows through R300.

Maybe this description helps other people with similar problems.

Could someone please help me out with a source of a spare part? I'm located in Germany and haven't contacted Keithley/Tektronix yet.

Best regards and a hot weekend
Robert