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Old 12th Oct 2019, 12:47 pm   #1
ValvoStef
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Default Fluke 70

Hi peeps,

Bit of a strange fault: I have a Fluke 71 multimeter, good 15 years old. Measuring AC and D.C. voltages is good, compared with two different meters, the values are accurate. However, when switching to Ohm range and shorting the test terminals with a piece of wire, the meter seems to be ‘counting up’, from 0.0 Ohms to about 15.x Ohms, the it stops. Initially I thought the battery is going to die soon, so I replaced it bur the Fluke is still doing the same. Leaving the meter without a battery for a while did not make a difference. Can this be a calibration issue or the beginning of the end of the meter?
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Old 12th Oct 2019, 1:40 pm   #2
linescan87
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Default Re: Fluke 71

I believe electolytics can leak and make the board conductive causing this. I've also seen damp cause this.
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Old 12th Oct 2019, 2:53 pm   #3
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Default Re: Fluke 71

Thanks for the info, I’ll check this out.
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Old 13th Oct 2019, 9:18 am   #4
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Default Re: Fluke 71

It may be a gap in my knowledge but I've not come across a Fluke DMM with the designation '71'. Also, I can't find reference to such a model via Google so just wondering if this is actually an earlier 70 series meter dating from the eighties? If it is, problems of this kind can often be traced back to dirty switch contacts. This is an easy fix, once the the PCA is extracted from the case, using a few squirts of switch cleaner/lubricant.

Alan
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Old 13th Oct 2019, 11:37 am   #5
Craig Sawyers
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Default Re: Fluke 71

Yes - leaky electrolytics are a known problem in older Fluke dvm's. I need to take the back off some of mine to check for that....

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Old 13th Oct 2019, 1:01 pm   #6
ValvoStef
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Default Re: Fluke 71

Quote:
Originally Posted by ajgriff View Post
It may be a gap in my knowledge but I've not come across a Fluke DMM with the designation '71'. Also, I can't find reference to such a model via Google so just wondering if this is actually an earlier 70 series meter dating from the eighties? If it is, problems of this kind can often be traced back to dirty switch contacts. This is an easy fix, once the the PCA is extracted from the case, using a few squirts of switch cleaner/lubricant.

Alan
Ahhh, of course it is a Fluke 70. You are right, Alan. Can’t even say it was a typo.
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Old 13th Oct 2019, 1:12 pm   #7
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Default Re: Fluke 70

Title updated and thread moved to vintage test equipment.
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Old 13th Oct 2019, 3:20 pm   #8
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Default Re: Fluke 70

I can't find details of the SIII Fluke 70 but the attached image shows the SII version's PCA. The four capacitors marked with crosses are electrolytic tantalums which are prone to physical leakage. C4 is an aluminium electrolytic and is less likely to leak. C2, C10 and C4 are concealed under the LCD panel. The panel can be removed complete with its frame by undoing the four screws on the reverse side of the PCA. For reference the switch is highlighted by an arrow should it be necessary to clean the contacts.

Alan
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Old 13th Oct 2019, 3:52 pm   #9
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Default Re: Fluke 70

Quote:
Originally Posted by ajgriff View Post
I can't find details of the SIII Fluke 70 but the attached image shows the SII version's PCA. The four capacitors marked with crosses are electrolytic tantalums which are prone to physical leakage. C4 is an aluminium electrolytic and is less likely to leak. C2, C10 and C4 are concealed under the LCD panel. The panel can be removed complete with its frame by undoing the four screws on the reverse side of the PCA. For reference the switch is highlighted by an arrow should it be necessary to clean the contacts.

Alan
Thanks, Alan, this is great help.
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Old 13th Oct 2019, 6:02 pm   #10
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Default Re: Fluke 70

Just a tip for anyone wishing to clean SI or SII switch contacts. Do not be tempted to rotate the switch using your fingers or other implements as it is very easy to distort/bend the contacts. Always put the PCA back in the case and operate the switch using its control knob. This ensures that everything is centralised and that no damage results. I speak from bitter experience! I've not had dealings with later 70 series meters but the same principle may apply.

Alan
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