My Fluke 115 is giving false AC reading. What can I do to repair it?

Thread Starter

Fabian Cerdas

Joined Apr 16, 2019
3
Hello, I am new to the forum so I apologize for any inconvenience.

I'm a student that needs your vast knowledge in meter electronics. As you read in my post title I have a Fluke 115. it's quite old, maybe 6 years old. It started presenting some problems like a year ago. Whenever I try to measure AC (doesn't matter if I have my leads attached or not) it presents a false reading. I know that meters tend to pick up charge over leads but the meter never did this much when it was new. This reading or offset is really annoying because I can't measure amps or volts below this value of 23 or 24 digits. As you can see DC is set to Zero but watch AC readings.

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Changing range values doesn't make a difference at all. This is my only meter BTW. I've disassembled the meter and applied some contact cleaner to every solder point without any luck. Board "looks" to be OK. I've tried testing the fuse and seems to be working perfectly according to Fluke booklets. I'm not an electronics expert so I come to you. Please help me diagnose this meter because taking it to a repair center costs almost the same as the meter. I live in Costa Rica.

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Thank you so much for your attention.
 

Thread Starter

Fabian Cerdas

Joined Apr 16, 2019
3
This is the calibration manual. If you can get a trusted source for the signals listed, calibrating it might be the answer.

Don't try to calibrate it unless you trust the source for the signals because that will be the standard for your measurements.

https://dam-assets.fluke.com/s3fs-public/114_____cieng0100.pdf
Thanks for your fast answer. You're right sir, it can be a calibration problem noting the longevity of the meter. I'm gonna look for any companies that have this calibrating equipment and can service it. I hope it doesn't break the bank.

Thank you sir.
 

crutschow

Joined Mar 14, 2008
34,201
I doubt that an offset zero reading is a calibration problem.
Sounds more like something in the AC portion of the circuit is oscillating or has failed.
That would be difficult to fix without a schematic.
 

Thread Starter

Fabian Cerdas

Joined Apr 16, 2019
3
I doubt that an offset zero reading is a calibration problem.
Sounds more like something in the AC portion of the circuit is oscillating or has failed.
That would be difficult to fix without a schematic.
It's a shame. I've never seen the schematics for this meter. Surely they exist but maybe only Fluke knows.
 

BR-549

Joined Sep 22, 2013
4,928
Wrap some tin foil around most(bottom half) of the meter.....leaving a peek hole for screen.

Ground foil.

Did meter zero?
 

LesJones

Joined Jan 8, 2017
4,174
Putting contact cleaner on soldered joints will not help. Contact cleaner is designed for use on switch or relay contacts. As your meter is quite old I would suspect dirty or worn contacts on the range selection switch. Before trying the contact cleaner on the switch make sure that it will not damage any of the plastic on the switch.

Les.
 

Wolframore

Joined Jan 21, 2019
2,609
Did you notice it's only on the AC setting.
This varies from model to model
It's the RMS converters which has a residual effect without inputs. It will cause offset to occur. The actual variance is tiny compared to what you measure so it's best to ignore this...

This is from the manual for the 87
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
28,576
A common problem with Fluke when the battery goes low.
Before the low warning comes on it gives wierd readings.
As I mentioned here before, I found out the hard way, also once a maintenance electrician came to me and said his meter was measuring 240v where 120v should be, I told him about the battery change and it cured his problem.
Max.
 
Last edited:

rsjsouza

Joined Apr 21, 2014
383
As others have said, short the inputs - it is not uncommon to have these residual voltages in AC (picks up noise from the ether)

A common problem with Fluke when the battery goes low.
Before the low warning comes on it gives wierd readings.
As I mentioned here before, I found out the hard way, also once a maintenance electrician came to me and said he was measuring 240v where 120v should be, I told him about the battery change and it cured his problem.
Max.
Wow, I don't recall this happening with my former 179 and it does not happen with my oldies 27/FM, 8060. That is quite dangerous at the voltage level you mentioned.
 
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