Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old February 3rd 08, 08:15 PM posted to sci.electronics.repair
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Default Fluke 79 acting up

This thing has performed flawlessly for many years, but when I turned it on
today something was not right. The ohms range flickers random readings, with
no probes plugged in I get around 230K on the display, or 2.22M, depending
on the range, which would imply that the problem is ahead of the scaling
circuit. When I switch to the low ohms range, the reading starts around 240
ohms and then drops to -0.00 over a period of 10 seconds or so, frequency
reading works, but AC volts reads 70mV when plugged into a 120V outlet.
Something strange is going on! I realized that I don't currently have a
backup meter, I suppose I could use this as an excuse to buy a true RMS
Fluke, I don't think I can bring myself to buy a cheapie, except perhaps as
a backup. Anyone run into this?



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Old February 3rd 08, 08:19 PM posted to sci.electronics.repair
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Default Fluke 79 acting up


"James Sweet" wrote in message
news:[email protected]
This thing has performed flawlessly for many years, but when I turned it
on today something was not right. The ohms range flickers random readings,
with no probes plugged in I get around 230K on the display, or 2.22M,
depending on the range, which would imply that the problem is ahead of the
scaling circuit. When I switch to the low ohms range, the reading starts
around 240 ohms and then drops to -0.00 over a period of 10 seconds or so,
frequency reading works, but AC volts reads 70mV when plugged into a 120V
outlet. Something strange is going on! I realized that I don't currently
have a backup meter, I suppose I could use this as an excuse to buy a true
RMS Fluke, I don't think I can bring myself to buy a cheapie, except
perhaps as a backup. Anyone run into this?


Sorry, it's a 77, not a 79.


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Old February 3rd 08, 08:29 PM posted to sci.electronics.repair
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Default Fluke 79 acting up

James Sweet wrote:

"James Sweet" wrote in message
news:[email protected]

This thing has performed flawlessly for many years, but when I turned it
on today something was not right. The ohms range flickers random readings,
with no probes plugged in I get around 230K on the display, or 2.22M,
depending on the range, which would imply that the problem is ahead of the
scaling circuit. When I switch to the low ohms range, the reading starts
around 240 ohms and then drops to -0.00 over a period of 10 seconds or so,
frequency reading works, but AC volts reads 70mV when plugged into a 120V
outlet. Something strange is going on! I realized that I don't currently
have a backup meter, I suppose I could use this as an excuse to buy a true
RMS Fluke, I don't think I can bring myself to buy a cheapie, except
perhaps as a backup. Anyone run into this?



Sorry, it's a 77, not a 79.


did you check the fuse in it?


--
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SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"

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Old February 3rd 08, 09:37 PM posted to sci.electronics.repair
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Default Fluke 79 acting up


James Sweet wrote in message
news:[email protected]
This thing has performed flawlessly for many years, but when I turned it

on
today something was not right. The ohms range flickers random readings,

with
no probes plugged in I get around 230K on the display, or 2.22M, depending
on the range, which would imply that the problem is ahead of the scaling
circuit. When I switch to the low ohms range, the reading starts around

240
ohms and then drops to -0.00 over a period of 10 seconds or so, frequency
reading works, but AC volts reads 70mV when plugged into a 120V outlet.
Something strange is going on! I realized that I don't currently have a
backup meter, I suppose I could use this as an excuse to buy a true RMS
Fluke, I don't think I can bring myself to buy a cheapie, except perhaps

as
a backup. Anyone run into this?




I invested in a moulded rubber surround for my 77, after repairing one
that had been jarred and the main SMD chip had loosened. Someone I know
managed to put his knee on his, while working on the floor, and also
dislodge the main chip. Both repaired after attending to the main chip.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/







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Old February 3rd 08, 10:18 PM posted to sci.electronics.repair
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Default Fluke 79 acting up

This might seem stupid, but have you checked the battery? Is the "lo bat"
annunciator displayed?




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Old February 4th 08, 05:10 AM posted to sci.electronics.repair
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Default Fluke 79 acting up



I invested in a moulded rubber surround for my 77, after repairing one
that had been jarred and the main SMD chip had loosened. Someone I know
managed to put his knee on his, while working on the floor, and also
dislodge the main chip. Both repaired after attending to the main chip.



I have the rubber surround, and it hasn't been jarred, it was sitting in the
closet where I always keep it.

I ordered a Fluke 187, I've wanted true RMS for a while anyway. When that
gets here I'll use it to try to fix the 77 and use that as a backup.


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Old February 4th 08, 05:11 AM posted to sci.electronics.repair
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Default Fluke 79 acting up


"William Sommerwerck" wrote in message
. ..
This might seem stupid, but have you checked the battery? Is the "lo bat"
annunciator displayed?




It's not displayed, but then I suppose it's worth checking the battery
anyway, I haven't, will do that tonight.


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Old February 4th 08, 11:19 AM posted to sci.electronics.repair
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Default Fluke 79 acting up


"James Sweet" wrote in message
news:[email protected]

"William Sommerwerck" wrote in message
. ..
This might seem stupid, but have you checked the battery? Is the "lo
bat"
annunciator displayed?




It's not displayed, but then I suppose it's worth checking the battery
anyway, I haven't, will do that tonight.



You should check its battery, that's where your problem is. Electronic
meters utilize A/D converter, the converter uses Voltage reference, when
battery is weak it give faulty voltage reference, as a result you get
faulty reading. Do not rely on voltage reading, sufficient voltages do not
mean sufficient Battery without enough current in battery.

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Old February 4th 08, 11:22 AM posted to sci.electronics.repair
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Default Fluke 79 acting up


"Jakthehammer" wrote in message
...

"James Sweet" wrote in message
news:[email protected]

"William Sommerwerck" wrote in message
. ..
This might seem stupid, but have you checked the battery? Is the "lo
bat"
annunciator displayed?




It's not displayed, but then I suppose it's worth checking the battery
anyway, I haven't, will do that tonight.



You should check its battery, that's where your problem is. Electronic
meters utilize A/D converter, the converter uses Voltage reference, when
battery is weak it give faulty voltage reference, as a result you get
faulty reading. Do not rely on voltage reading, sufficient voltages do
not
mean sufficient Battery without enough current in battery.



Sorry if I confuse you, let me try again:

You should check its battery, that's where your problem is. Electronic
meters utilize A/D converter. The A/D converter uses bat as Voltage
reference, when battery is weak it gives faulty reference, as a result you
get faulty reading. Change the battery with fully charge.

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Old February 4th 08, 01:37 PM posted to sci.electronics.repair
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Default Fluke 79 acting up

"Jakthehammer" wrote in message
...

You should check its battery, that's where your problem is.
Electronic meters utilize A/D converter. The A/D converter
uses bat as Voltage reference...


Actually, a semiconductor device similar to a Zener diode is used as the
voltage reference. But the battery has to be at or above the device's
threshold to provide a stable reference.




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