Author Topic: Fluke 73 , Ohm Autranging at 30MOhm, faulty or not ?  (Read 1427 times)

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Offline JuergenB52

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Fluke 73 , Ohm Autranging at 30MOhm, faulty or not ?
« on: June 21, 2013, 06:29:19 pm »
Hi,

i have an old Fluke 73, it reads all Voltages, Ohm, Currents, etc fine.

But if i set it to Ohm and do not connect any test leads, it´s autoranging.
It starts about 10MOhm and climbs up to 30MOhm.

My Fluke 179 or 77 Show O.L MOhm.

Is this a normal behavior for the Fluke 73 series?

The 1kOhm fusible has been exchanged.
Thank

Jürgen
 

Offline Excavatoree

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Re: Fluke 73 , Ohm Autranging at 30MOhm, faulty or not ?
« Reply #1 on: June 21, 2013, 06:52:29 pm »
Typically, the 73 should also show OL.   I'd check the board for contamination or carbon traces, and check the input MOVS.


 

Offline JuergenB52

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Re: Fluke 73 , Ohm Autranging at 30MOhm, faulty or not ?
« Reply #2 on: June 22, 2013, 12:57:43 pm »
Hi,

i checked the MOV´s and i removed them, and cleaned the PCB.

Directly after cleaning the PCB around the Input Jacks with isopropanol alcohol it goes down to 1MOhm,
after a while it starts with OL and goes down to 25-31MOhm.

Can the Rotary Switch be faulty?

Thanks for the help
 

Offline ModemHead

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Re: Fluke 73 , Ohm Autranging at 30MOhm, faulty or not ?
« Reply #3 on: June 23, 2013, 08:36:37 pm »
Turn the board over and look for the QFP analog processor on the bottom nearest the input jacks.  Use something fairly sharp and drag it between all the pins.  Don't press hard enough to damage anything, just make sure there is no crud or contamination between the pins.  Then re-clean it vigorously with a brush and IPA.  Allow to dry thoroughly.  IPA may collect under the chip.  Blow it out and/or warm it gently under a lamp.
 


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