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Old 12th August 2010, 04:49 AM   #1
jlovda is offline jlovda  United States
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Default Fluke 75 Multimeter Problem

I just obtained a Fluke 75 (version I believe) for $10 at a flea market. It is very clean and the DC voltage function seems to work fine. The problem is that for low resistance values such as 1, 10, 100 up to about 1K ohms, the meter is way off. Usually about half the actual value. Above 1K the readings are within the tolerance level of the resistor. I measured the large fusible resistor that was mentioned in previous posts as a possible cause and it is about 1K ohm with out lifting one side off the board. One curious thing on the board is there are several red devices that look like tantalum capacitors but they have a razor thin cut half way through them. Any ideas what these are? Any suggestions where to look. Anyone know where o get a free schematic off the internet? Thanks
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Old 12th August 2010, 07:15 AM   #2
Mooly is offline Mooly  United Kingdom
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Most problems with meters are down to abuse... if you are lucky just a resistor or two burned or gone high. Worth measuring them all.

The "red bits" sound like caps with integral spark gaps... or just spark gaps.
Common in protection against CRT flashover in TV's.

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Old 12th August 2010, 12:23 PM   #3
jlovda is offline jlovda  United States
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Quote:
Originally Posted by Mooly View Post
Most problems with meters are down to abuse... if you are lucky just a resistor or two burned or gone high. Worth measuring them all.
I have tried to avoid lifting one side of resistors in order to measure them. I will have to start doing that. I keep looking at the circuit board with a backlight hoping that some of the resistors end at open circuit points such as switches or the input posts.

There is a thin white rectangular device with about 10 leads soldered to the board. Is this where all the precision film or vapor deposited resistors reside that are used for the references?

Thanks,
John
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Old 12th August 2010, 06:00 PM   #4
Mooly is offline Mooly  United Kingdom
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Almost certain to be a thin film resistor network.

Don't know where you would get a circuit but it's what you need really.
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Old 12th August 2010, 11:44 PM   #5
Enzo is offline Enzo  United States
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Um, is the battery fresh? Funny resistance readings can result when the 9v battery is about 5v.
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