Fluke 287 inaccuracy in upper 50k Ω range

[Els_Chaos]

Hi everyone, i just got a secondhand fluke 287 (because I'm still a student with limit budget) but i found out that the upper 50k Ω range show significantly wrong when compared to the others i got is Aneng Q1, Apech AC-286 (although it's purpose is a current clamp) and color in the resistor that i had (some is ± 1 and ± 5%, i don't have precision resistor).
here is the data i got in case of attachments can't be load properly :

My question is that does calibration help to make it becomes accuracy? Or because the hardware is corrupted?
 (I'm so sorry this is my first post therefore maybe i have some typo, wrong grammar and very little experience in this field)

[Fungus]

Show some example readings... what's the error?

[Els_Chaos]

It measured value is too big when comparing to the others multimeter

[Fungus]

It measured value is too big when comparing to the others multimeter

How big?

[tooki]

It measured value is too big when comparing to the others multimeter

How big?

Are you not seeing the screenshot embedded right in the original post?!?

If it's not appearing for you, use the Quote button to see the original post's source code so you can get the URL.

[AVGresponding]

You might want to open the case and see if the supercap has leaked, or if there's any evidence of battery leakage.

[Els_Chaos]

The supercap is a little bit old,  may i need to replace it?

[Fungus]

Are you not seeing the screenshot embedded right in the original post?!?

No.

[tom66]

Reuploading the screenshot for the OP.  It's hosted on Imgur embedded which some adblockers don't allow.

[AVGresponding]

The supercap is a little bit old,  may i need to replace it?

It's certainly something to be aware of. They are easily available, and not expensive, but if they leak and it isn't cleaned up, it can cause damage

[Fungus]

68k, 100k, 300k are all on the same range (50k-500k).

4.7M is a different range (500k to 5M)

What does it say for a 470k resistor? What does it say for a 680k resistor?

[Els_Chaos]

for 680k ± 1% resistor it came up with the reading of 715.9kΩ. for 470k ± 1%, the result is 495.3 kΩ 

[Els_Chaos]

could i get its part number please

[AVGresponding]

could i get its part number please

https://www.eevblog.com/forum/repair/fluke-289-super-capacitor/

[Ugur]

Varistors at the input may also be a problem.

[BeBuLamar]

the 287 has a lifetime warranty do does Fluke covers the supercap?

[Els_Chaos]

Excuse me, how can i check if them is still good sir

[Els_Chaos]

Here is the image of that capacitor. It seems like that there is some enroded oxide around the cap.

[Els_Chaos]

I measured the resistance between 2 legs of each RV (the blue one). 2 of them showed open circuit but 1 (nearest 10A shunt resistor) showed up 18.89M ohm. Is it bad?

[Els_Chaos]

I just made a measurement with aneng q1.  The value of measured component is written in the image. The OC stands for open circuit

[BeBuLamar]

I would contact Fluke and have them repair it for free. Fluke never asks you to prove where you bought the meter. Oh I didn't realize that you're in Vietnam.

[Els_Chaos]

It is a little bit hard for me in Vietnam. Although it actually has retailer in vietnam but i dont know will they accept repair a 2nd one

[bdunham7]

A couple of observations for you:

1) You can simply remove the super cap and clean the board area around it.  The meter will be nearly fully functional (only some memory/RTC functions use it) and you will be able to do all of your tests and work without replacing it.

2) Your erroneous resistance measurements are high, not low.  Input protection MOVs and other components cannot be the cause of high readings, only low. 

3)  The accuracy of meters is not that good at high resistances, from 5M to 50M it is 1.5%, from 50M to 100M it is 3% and above 100M it is 8%. 

The first things to check when you have an issue like this are the test current and compliance voltage.  So take another DMM that has a 10M input impedance, connect the two together and set the 287 to resistance and the other to volts and then to current.  See if those output voltages match up to what is shown in the manual.  High resistance readings only in the upper parts of the range is a pretty strange symptom, IDK offhand what would cause that. 

[Els_Chaos]

do i need to bring this to calibrating service sir? As i read some posts in EEVBlog, they said that the Varistor should show Open circui and could you tell me more clearly how to check if the resistance measuring is good sir.

[AVGresponding]

I just made a measurement with aneng q1.  The value of measured component is written in the image. The OC stands for open circuit

The two that measure 1k are good; that's what they should. RV1 should measure OC like the RV2 and RV3. It connects across system GND and the guard traces, and is in series with RV2 and RV3 from the VΩ jack.

I suspect there's some contamination on the board. Give it a good clean, and measure it again. If it still is measureable, unsolder it and measure again. If it's measurable, then it needs replacing. If it ins't, once out of the board, then the board still needs cleaning some more...