Need help Repair Fluke 179 - Ohms / Diode Failure

[JuergenB52]

Hi,

i got a cheap Fluke 179 from ebay, meter is 3 month old.
the meter has been used at the ohm range during voltage measurement.

With some resistor of 25Ohm it reads 12.5Ohms.

I had read several service manuals of similar meters.
The RT1, R1 and MOV´s seem to be fine?

Could the resistore network be bad or the Q1 and Q2?

I have some cheap Fluke 124 and 73 Multimeter for testing the 179.

Juergen

[Bloch]

Why fit it yourself ?

http://www.fluke.com/fluke/usen/digital-multimeters/fluke-170.htm?PID=56027

Lifetime warranty

[JuergenB52]

Hi Lars,

Lifetime is only for the first owner.
And they will not provide warranty for wrong handling.

Juergen

[Bloch]

That sucks FLUKE 


Without a schematics it is hard to help you out. But try to follow there the traces go and check the components you find...

[JuergenB52]

Thanks,
i can't find any smeg for the 179 , but a lot for the older ones.
The normal MOV's and the thermistor are fine.

I think i'll call fluke tommorow and ask them.

They claim service, but don't answer mails...
I think i'll Check Q1 and Q2 next, and finally the resistor Network.

Does anyone has some more information for the rnet (Z1) spare part number?

Juergen

[retiredcaps]

the meter has been used at the ohm range during voltage measurement.

Hmm, I'm surprised.  We have all seen Dave do the mains/ohms overload test on various Flukes and they all survived.

With some resistor of 25Ohm it reads 12.5Ohms.

Do all resistors read 1/2 of its value?

[JuergenB52]

Hi,

I did some Tests.

25 reads 12.5
50 reads 25
75 reads 37.5

46k reads 42k

Open leads reads 459kOhm

 Maybe the Switch? I will try and shorten the Contador for Ohm meassurement.

[retiredcaps]

Maybe the Switch?

Are your AC and DC V readings okay?  Or are they off as well?

Cleaning the range switch could help.

If the multimeter was used in a very dirty environment you may need to give the entire PCB a good wash like I did for my Fluke 77 II??? See

https://www.eevblog.com/forum/general-chat/fluke-77-ii-incorrect-readings-on-all-ranges/

[JuergenB52]

Hi,

i don´t think so, the meter is 2 month old and was used for resistor measurement.
the last measurement was at ohm range and voltage was measured.

but i will check today.

[ModemHead]

It does suck that schematics aren't available for the newer models.  Makes it quite difficult to self-service.  On top of that, the white plastic LCD/cover assembly has to be off to access any components.

If trouble-shooting is your best option, then the starting assumption is that something has failed due to over-voltage while on the Ohms range.  Since it's reading low, perhaps there is a failed component across the inputs.  Take the battery out, set the range switch to Ohms, and take a resistance measurement across the input terminals with another DMM.  I have a 179 here, it measures 3.6 MOhms, so if you get a significantly lower measurement, you'll have to find which component is leaking the extra current.

There are transistors near the range switch.  Using another DMM in diode check mode, test that the B-E junction of each one reads about 0.6V, and open in the E-B direction.

Hope this helps.

[JuergenB52]

Hi,
i think i need to shame myself ...

I did some tests with the fluke 179 and my old 73.
i got some new leads today and some 0.1% resistors for test purpose.

i checked the Input resistance of the fluke 179, no battery and the switch set to Ohm range, i got 3.6 MOhm.

next i checked some resistors with fluke 73. 25 , 100 , 46kOhm.
All are fine with fluke 73 (all auto range)

next i used the Fluke 179

with autorange i get   12.5 , 50 , 42kOhm for 25, 100, 46k

with manual range (MR) range/xxx i get with a 100 Ohm 0.1% and a 25 Ohm
O = Ohm

MR O/600    50        12.5
MR kO/6      0.1       0.026
MR kO/60    0.10     0.03
MR kO/600  0.1       0.0

did i miss some problems with fluke 179 and autorange settings?
i get the feeling if i set the manual range higher and higher the DMM gets more precise?

a 830kOhm reads with a half value, only in MR MO/600 i get 828kO?

caps are worse, the get different readings, new 1000uF are read with 2400uF and 220uF are read as 500uF.

diode seems to be fine?

any idea?

[retiredcaps]

The RT1, R1 and MOV´s seem to be fine?

Pardon me for asking, but what are the actual measurements of all the above components?

[ejeffrey]

No, it just looks like your lowest resistance range (600 ohm) has a damaged reference.  The auto-ranging doesn't know to avoid it, so it goes into the damaged range on low values.  When you put it on the higher ranges you loose a little bit of resolution, but at least it works.

I don't know what the resistance circuit on the meter looks like, but the fact that you are reading exactly half sounds like a Clue (TM).  Something like two identical resistors in parallel, with one of them fused.  If you had a schematic you should be able to figure out what components are most likely damaged by applying HV on ohms mode, and which of those could give a 2:1 error on only a single range.

The capacitance measurement is roughly the same problem.  Caps are measured by applying the same current sources used in ohms mode and seeing how long it takes to charge up.  With half the current you get double the value.  That puts you well in range of the -20/+80% tolerance of typical electrolytic PSU caps.

Diode mode works fine because the diode forward voltage is very insensitive to current, only changing 10s of mV for a 2x change in current.

The smaller errors on the higher ranges could be caused by additional minor damage from the same root cause, or it could be that the particular circuit topology keeps the resistors from the circuit for the higher ranges.  Or the voltage reference could be off. 

[JuergenB52]

RT1 was at 1.1kOhm
R1 as indicated by the color code
MOV where high Ohm, abot 25MOhm

i didn't remove them from the PCB

[ModemHead]

Are your AC and DC V readings okay?  Or are they off as well?

I haven't seen the answer to that question yet.  If it reads voltage correctly, then the key parts of the meter are still working, maybe it's the Ohms current source or associated voltage sensing.  I think those same paths are used for cap measurement also.

I like ejeffrey's thinking...

[JuergenB52]

Voltage and current is fine, it seems that the reference resistor network has a problem.

i thought that the fluke 179 with thermistor and MOV should be safe for voltage input at Ohm range.
the info from ejeffrey sounds reasonable.

i called fluke today and they said, they "might" repair on warranty.

i think the resistor network is expensive to get.

[ModemHead]

Do you have an idea of the magnitude of the over-voltage?  That would be interesting to know, if only for future reference.  I have accidentally applied mains voltage to the ohms range before with no problems.

[JuergenB52]

Hi,

i had send the meter to fluke for repair.
they told me that it has been destroyed by user error.

The undervoltage protection is broken!
can someone explain to me what this means, can i repair it?

They want to charge me 203 € for repair (including vat and shipping), actually i get a new one.
If i don't want to get it repair i have to pay 80 € for diagnostics.

They ask if i want a calibration certificate for 55€ , is this really necessary for home / hobby use?

A new fluke 179 will cost me 280 €

but i will get all this

Fluke 1AC Volt Alter
Fluke C35 Holster
Fluke TL224 Probe
Fluke TP220 Probe
Fluke AC220 Probe
Fluke 80BK Temp Probe

and a

Fluke 179 RMS Multimeter

Maybe i can sell this stuff to eBay and get a fine fluke 179 for about 150€

any idea's are welcome

Jürgen

[retiredcaps]

Do you have an idea of the magnitude of the over-voltage?

@JuergenB52 Did we get an answer to the above question? That might help us with some of your questions?

The most I can generate at home with no equipment is mains 120V AC or 165V DC from a large filter capacitor.

[JuergenB52]

Hi,

sorry i haven´t any information about the overvoltage.

Maybe it´s 220V at the ohms, i don´t know.
i talked with fluke service repair.

They will swap the meter for a brandnew boxed fluke 179, with probes and a temp prob.
I think it´s called in english "to pay dearly"or "to learn the hard way".

it take too much time to find the cause or cheap repair.

I learned my lesson, not to buy cheap meters at ebay 

But it´s the fasted way now.

it think the voltage was to much for the meter.

Thanks

Jürgen

[retiredcaps]

I had mainly good luck so far getting used working Flukes.  They all seem to be in spec and everything works, but until I make a mistake, I guess I won't know for sure.

[Rick]

If you buy second hand flukes 83, 87 and ask the seller to connect the V-Ohm terminal to the mA/uA terminal as Dave was explaining recently (I have myself learnt from that thread), you can at least get some clue about the fuses or whether  the meter is more or less fine. I asked one seller to run that test. It turned out the fuses are blown but the capacitance value seems to be the same as on my used but extremely nice and clean fluke 83, when no terminal is connected. In another case I asked the seller of a bench multimeter 8840A to run a self test it turned out it misses the option 09 (rms option, tests 1 2 3 are skipped and I don't know if it is possible to install it; is it a separate board?), but the guy was nice to run the test and admit it (he sent the video of the test). At least you know what you are buying. Actually I am not going to buy it, not being able to repair such stuff...

[Excavatoree]

... In another case I asked the seller of a bench multimeter 8840A to run a self test it turned out it misses the option 09 (rms option, tests 1 2 3 are skipped and I don't know if it is possible to install it; is it a separate board?), ...

I'm told it is an installable module, but I'm also told they are very rare and difficult to obtain.  You probably know the same E-bay seller I do who sells many of these with the 09 option installed, and a warning to be sure the meter you buy has it if you need it.