FLUKE 374 CLAMP TESTER DIAGRAMS? OHMS RESISTANCE SCALE FAULT - Page 1
Forum section: electronics / repair

author: harrimansat
author_rank: Regular Contributor
timestamp: June 22, 2015, 04:40:48 pm
content: Hi, I have a FLUKE 374, all functions works, except resistance scale, someone have diagrams for this meter?Thanks

author: retiredcaps
author_rank: Super Contributor
timestamp: June 22, 2015, 05:40:45 pm
content: 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

author: retiredcaps
author_rank: Super Contributor
timestamp: June 22, 2015, 05:44:56 pm
content: Quote from: harrimansat on June 22, 2015, 04:40:48 pmI forgot to ask what is wrong with the resistance measurements? Is it not accurate or doesn't work at all?

author: retiredcaps
author_rank: Super Contributor
timestamp: June 22, 2015, 05:56:47 pm
content: BTW, if your 374 been recalled, Fluke might fix your problem for free under warranty/safety recall. Seehttp://www.fluke.com/fluke/caen/support/safety/37x-recall

author: harrimansat
author_rank: Regular Contributor
timestamp: June 22, 2015, 08:04:01 pm
content: Quote from: retiredcaps on June 22, 2015, 05:44:56 pmThere 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.

author: retiredcaps
author_rank: Super Contributor
timestamp: June 23, 2015, 06:30:43 am
content: Quote from: harrimansat on June 22, 2015, 08:04:01 pmHmm, 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!

author: retiredcaps
author_rank: Super Contributor
timestamp: June 23, 2015, 07:12:36 am
content: BTW, did this problem just start happening by itself? Or was it a victim of an oops moment?

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: June 23, 2015, 10:27:46 am
content: Quote from: harrimansat on June 22, 2015, 08:04:01 pmI'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.

author: harrimansat
author_rank: Regular Contributor
timestamp: June 24, 2015, 03:18:59 pm
content: Quote from: retiredcaps on June 23, 2015, 07:12:36 amWas a vitim of an oops moment

author: harrimansat
author_rank: Regular Contributor
timestamp: June 24, 2015, 03:23:44 pm
content: Quote from: medvedev on June 23, 2015, 10:27:46 amThis meter is autorrange. There are two 4053 near inputs.