FLUKE 374 CLAMP TESTER DIAGRAMS? OHMS RESISTANCE SCALE FAULT

[harrimansat]

Hi, I have a FLUKE 374, all functions works, except resistance scale, someone have diagrams for this meter?
Thanks

[retiredcaps]

Clamp meters is one area where I haven't done any research so there might be a schematic/service manual for it.

Almost every modern handheld Fluke meter has similar input protection.  Usually, you will a varistor (MOV), thermistor (PTC) and and fusible resistor.

Circled in blue, that green colored component on the other side of the pcb looks like a PTC.  You can measure its resistance in circuit initially.  It should be around 1k ohm.  If it is significantly more, desolder it and verify out of circuit.

If you post a picture of the other side of the pcb, I can verify if that green component is a PTC or not.

If the PTC is bad, you can temporarily replace it with a normal 1k ohm resistor for testing purposes.  If resistance then works, then get the correct part which is likely YS4020, but availability is difficult/impossible.

http://datasheet.octopart.com/YS4020-Thermometrics-datasheet-11237.pdf

[retiredcaps]

Hi, I have a FLUKE 374, all functions works, except resistance scale, someone have diagrams for this meter?

I forgot to ask what is wrong with the resistance measurements?  Is it not accurate or doesn't work at all?

[retiredcaps]

BTW, if your 374 been recalled, Fluke might fix your problem for free under warranty/safety recall.  See

http://www.fluke.com/fluke/caen/support/safety/37x-recall

[harrimansat]

Hi, I have a FLUKE 374, all functions works, except resistance scale, someone have diagrams for this meter?

I forgot to ask what is wrong with the resistance measurements?  Is it not accurate or doesn't work at all?

There is low output voltage when in ohms 0 to 0.2 V, output voltage fluctuates itself between 0 and 0.2 volts, and ohm read too. Could be is current source fault. But where is???
PTC fuses, varistors, and R IN are ok.

[retiredcaps]

There is low output voltage when in ohms 0 to 0.2 V, output voltage fluctuates itself between 0 and 0.2 volts, and ohm read too. Could be is current source fault. But where is???

Hmm, 0 to 0.2V is low. I have a couple of ideas, but I will have to do some searching/research to see if I'm right or not. It will take me a couple of days as I'm trying to enjoy summer in here Canada! 

[retiredcaps]

BTW, did this problem just start happening by itself?  Or was it a victim of an oops moment?

[ElektronikLabor]

Could be is current source fault. But where is???

I've got a Philips Bench DMM with the same problem: When switched to the Resistor-measuring funktion, the current is fluctuating but only during one range; all other ranges work fine. Can you manually change the ranges? Are all ranges faulty?

Indeed, on the Philips DMM the current source is faulty. I found it out by reverse engineering the DMM.
You could switch the Clamp to Resistor mode and try to figure out the signal path (with continuity mode of a DMM). Using this approach you could find the current source.

[harrimansat]

BTW, did this problem just start happening by itself?  Or was it a victim of an oops moment?

Was a vitim of an oops moment

[harrimansat]

Could be is current source fault. But where is???

I've got a Philips Bench DMM with the same problem: When switched to the Resistor-measuring funktion, the current is fluctuating but only during one range; all other ranges work fine. Can you manually change the ranges? Are all ranges faulty?

Indeed, on the Philips DMM the current source is faulty. I found it out by reverse engineering the DMM.
You could switch the Clamp to Resistor mode and try to figure out the signal path (with continuity mode of a DMM). Using this approach you could find the current source.

This meter is autorrange. There are two 4053 near inputs.