Help Fluke 8845 can't read resistance value

[qnhn90]

hi all
i have 1 ea fluke 8845 can't read resistance value.
Do you have a way to handle it thoroughly?
I can only measure up to 170k ohm.
and then other higher values ​​cannot be measured.

[bdunham7]

Are you saying that it reads **accurately** up to 170K, but then displays 'OVERLOAD' for anything higher than that?  Or is it inaccurate?

[qnhn90]

If the value is higher, it is still only displayed at 170k ohm. no more.

[Kleinstein]

Is the 170 K upper limit fixed, independent of the range (e.g. 2 M or 20 M range) ?

It could be something like the Ohms current source not able to provide a higher voltage or some additional resistance across the inputs (e.g. a bad MOV, bad Ohms source protection circuit, dirty board (leaking cap, fried bug).

A test worth while may be checking if the voltage reading input is also high impedance as it should. One can do this by charging a small cap (like 1-10 n) to some 10 V and than check how fast the capacitors discharges when measuring the voltage.

[bdunham7]

If the value is higher, it is still only displayed at 170k ohm. no more.

OK, I assume this is on the 1 megohm range.  First, try manually putting it in the 10 megohm range and see what the reading is for a larger resistor.  Then use another meter with at least a 10M input impedance and measure the voltage output of the 8845A in the 1M and 10M resistance ranges.

Have you had the meter for a while and this all suddenly just happened or did you get it with this problem?

[wn1fju]

I've had several "broken" meters (not this particular Fluke model) that behaved strangely.  Finding nothing overtly wrong with the circuitry, I ran through the calibration
procedure and things then worked fine.  It seems that a lot of times, the calibration constants get corrupted and the meter will produce erroneous results until they are
overwritten with values that make sense.

[mzacharias]

I would use another multimeter to measure the input resistance of the Fluke on its DC volts mode.

I'm betting a damaged part in the front end, coincidentally measuring - wait for it - 170K