Fluke 187 strange problem

[DK ekectro]

Hi to all,
I need some help for reparing half dead Fluke 187.
I normally service electronic devices, but trying to repair this dmm gives me a headache. I have a strange problem with this instrument. When it is turned on, no matter which measuring range is set it always just writes OL and the bargraph is always at maximum and does not react to measurements as if the test probes are not connected.
Another problem is that when switching to continuity mode it always beeps constantly without or with plugged test leads. Here are the results of some of my measurements on it:
1. All measuring ranges can be selected and all this is neatly displayed on the screen.
2. Everything is reset to factory settings but no change.
3. All terminals are clean and in the measuring range for uA and mA it correctly detects whether the test leads are plugged or not.
4. All protective resistors and other elements on the input side are measured and ok.
These are the measured resistance values ​​with the other instrument when the probes are connected to its COM + Resistor, Voltage, Diode terminals while it is off.
5. Vac-0 Ohm
6. mVac-0 Ohm
7. Vdc-0 Ohm
8. mVdc-0 Ohm
9. Ohm, nS, Con.-1 Mega Ohm.
10. Diode, Cap.-1.47 Mega Ohm.
11. Temp.-1.48 Mega Ohm.
12. mAac-0 Ohm.
13. uAac-0 Ohm.
14. mA-0 Ohm.
15. mAdc-0 Ohm.
16. uAdc-0 Ohm.
All contacts on the rotary switch are clean and ok.
The thin white resistive network is tested and all values ​​are ok.
There are no traces of dirt or corrosion but I just don't know what could be the cause ...? I ask for any help or advice.
P.S. sorry in my english.

[daisizhou]

How did you clean the 4 terminals?

[DK ekectro]

Hi, with IPA. I don't have ultrasonic cleaner and i don't have schematics for Fluke 187 only downloaded chinese version of some repair manual... 

[daisizhou]

It is recommended to use 95% alcohol solution for soaking.
Yes, some forums in China have detailed fixes, but only if you identify where the fault is.
I am using 187 myself

[DK ekectro]

Thank's for replay!
I also programed his 93c56 eeprom with new dump but it didn't help, still the same thing.
I will try new cleaning with alcohol and post results...

[DK ekectro]

And what could be the problem when i switch to continuity test or diode test it just constantly beeps like there is a short beetwen input terminals. How much input impedance must bee when it is set to continuity mode...?

[daisizhou]

No, it must be soaked in alcohol, there is no exact resistance value
It is best to use a syringe to flush
Dry or soak in the sun after it's all done

[mzacharias]

I think I would try opening the meter, and shorting the backup capacitor briefly.

Who knows? Maybe it's just locked up somehow?

[DK ekectro]

Just to thank everyone for the good advice and to say that soaking in 95 percent alcohol did not help and as for the advice to short circuit the super capacitor it unfortunately does not work because Fluke 187 does not have such a capacitor as the model Fluke 189.

[daisizhou]

look picture

[srmahaffy]

Hi, I wanted to report, that I had similar beeping issue on a Fluke 87. It was a either a 87iii or 87V. To correct it, I reflowed the solder for each of the three input ports. In your case, it would be four.

[mslr]

Are these burn marks on the PCB? Last picture, left to the 100n through hole white capacitor and left of the turning switch? Not clearly visible on the picture.

[Ugur]

Hello ,
The input terminal is faulty, you need to replace it.
To be sure, you can try removing the input terminal from the device.

[DK ekectro]

Hello to anyone who got involved and helped locate the error. I apologize to everyone for not answering for a long time... I tried all your tips and even suspected myself that the biggest problem might be in the terminals, I desoldered them from the PCB but the problem still remained so I suspected that the problem might be in the inner layer itself. Ultrasonic cleaning might help, who knows, but I gave up trying so I sold it in such a defective state.   Thank you all!