Fluke 36 Clamp wont get DC amp near zero

[fplenin]

Hi everybody

I just bought an used Fluke 36 clamp (really cheap price) and when I try to measure DC amp (1000A or 200A) it measures 40-70 Amps when there's nothing inside the clamp...it should be near zero (my UNI-T reads 0.04 Amps) . The adjustment (DC Zero) just increases or decreases 10 Amps from the measure, but still pretty far away from 0 Amps.

Voltage (AC and DC) and AC Amps are measured correctly (I have a UNI-T clamp to compare). Ohms makes a beep when both terminals gets in contact.

What do you think is wrong with it?

[retiredcaps]

Currently, no idea, but post clear focused pictures of the pcb inside (both sides) and maybe we can spot something obviously wrong?

[Kleinstein]

DC current measurement is not simple with a clamp meter.

One possibility is that the core is somehow magnetized, e.g. from a large current or external magent in the past. One could try demanetizing it by measure a high and than reduced  AC current.

Also a external magnetic (DC) field could abset upset the probe, when measuring DC currents.

[fplenin]

Kleinstein, what's "abset"? I can't find it in the dictionary and english isn't my native language
_____________________
RetiredCaps: I disassembled the tool to take the pictures and it kind of magically started to work...first it was at about 6 Amps DC inteast of Zero, then I moved the DC Zero adjustment and set it at exact 0.0 (+/- 0.1 Amps). Then I toke it and measured 3.1 Amps DC and then used my almost new UNI-T 204 and it measured 3.5/3.6 Amps DC (used an UPS with external batteries and toke the AC power off the UPS and measured how much current was going out of the batteries).

I'm not sure which one is closer to the real Amps value, but I can surely say that the Fluke is suddently working closer to something useful.

The thing I noticed was a little bit of dirt around the function selector and I cleaned using alcohol. Toke pics and reassembled.
Pictures:
http://postimg.org/image/kbbvrzcl3/
http://postimg.org/image/si6uvz5pd/
http://postimg.org/image/o6mukpo69/
http://postimg.org/image/oxwwk56b3/

What do you think

[retiredcaps]

Kleinstein, what's "abset"? I can't find it in the dictionary and english isn't my native language

He probably means "upset".

The thing I noticed was a little bit of dirt around the function selector and I cleaned using alcohol. Toke pics and reassembled.

Dirt and debris, aka contamination, on the pcb can cause all sorts of funny readings.

[IconicPCB]

Dirt on the PCB might be a problem.
A major issue is related to the dirt within the clamp causing improper mating of the clamp surfaces.
Clean out the mechanism and ensure the clamp closes fully.

[fplenin]

Is it ok to clean all the PCB of a clamp or multimeter with spray contact cleaner?
Some advice?

I'm asking because once I damaged a cellphone speaker-microphone with contact cleaner...

[retiredcaps]

Is it ok to clean all the PCB of a clamp or multimeter with spray contact cleaner?

I suggest IPA only for the pcb.  The more pure the better and allow ample time for the pcb to dry (overnight) or use a fan.

Contact cleaner is okay for push button switches like on a Fluke 8020A multimeter, but not for the pcb.