FLUKE 179 problems

[bwilliams60]

Good Evening, I have a Fluke 179 that won't measure resistance at all and the ammeter always reads negative although the amperage seems to be close to accurate. On DCV, measuring a 9VDC battery, it shows 8.34 VDC when connected with proper polarity and -1.328 VDC when reversed.
I am guessing this was connected to voltage when measuring resistance. Does anyone have a schematic or a good place to look on these units. The traces are hard to follow and they are layered and well masked. Looking for guys who have experience with these meters please.
Both fuses have been tested and are in good condition. Battery has been changed and makes no difference, measuring 9.13 VDC

[stj]

Re: FLUKE 179 problems

there is a "supercap" in some fluke meters that leaks - check that out.

[retiredcaps]

Re: FLUKE 179 problems

there is a "supercap" in some fluke meters that leaks - check that out.

The supercap doesn't affect the Fluke 170 series.

[retiredcaps]

Re: FLUKE 179 problems

I am guessing this was connected to voltage when measuring resistance.

Likely.

Does anyone have a schematic or a good place to look on these units.

You won't find a schematic for the Fluke 170 series.

Both fuses have been tested and are in good condition.

The fuses have no bearing on the resistance or voltage measurement of the meter, only current.

I'm guessing the input protection is damaged.

1. Post a clear focused picture of your pcb (both sides).
2. The varistors or MOVs in your meter should all measure infinite resistance.
3. The PTC should measure around 1.0k ohm.
4. The fusible resistor should measure around 1.0k ohm.

Measurements can be made in circuit for 2, 3 and 4. If the readings are not as I suggested, then desolder the components to verify.

[redwire]

Re: FLUKE 179 problems

I'd check the two diode-connected transistor clamps, there are the only parts I can think of that can cause a symmetry problem with polarity.

There's two sets of them under the big Dale power resistor.

[retiredcaps]

Re: FLUKE 179 problems

I'd check the two diode-connected transistor clamps, there are the only parts I can think of that can cause a symmetry problem with polarity.

There's two sets of them under the big Dale power resistor.

A case of bad diode transistor clamps ...

https://www.eevblog.com/forum/repair...pair-question/

BTW, there is a parallel thread running on eevblog.

https://www.eevblog.com/forum/beginn...9-not-working/

[bwilliams60]

Re: FLUKE 179 problems

Thank you all for your comments. With respect to the parallel threads, no harm in using resources. I respect all who answer and those who don't, but I see no harm in asking more than one body.
I will test as suggested and I only mentioned the fuses etc to show the state of the unit. As for the state it was in when I got it, just as I have described. It came to me as a dead unit with exactly what you read going on. Prior to that, it had sat in a toolbox for a while. It is a very clean unit.

[stj]

Re: FLUKE 179 problems

if you set it to ohms without any leads connected, do you get a reading?

[bwilliams60]

Re: FLUKE 179 problems

Okay here is what I have.
All three varistors read O.L.
The PTC reads 1.095 k Ohms
The resistor measures 1.05 kOhms
The resistor bank = 1M ohms

[retiredcaps]

Re: FLUKE 179 problems

Okay here is what I have.
All three varistors read O.L.
The PTC reads 1.095 k Ohms
The resistor measures 1.05 kOhms
The resistor bank = 1M ohms

Those readings look correct. Can you take a picture of the pcb with the white plastic removed? We need to see if there is any obvious damage to the rotary switch.

1. With no probes and meter set to ohms, what does the display show?
2. With probes shorted and meter set to ohms, what does the display show?
3. If you measure a 1k ohm resistor, what does the display show?

[bwilliams60]

Re: FLUKE 179 problems

1. No probes = O.L.
2. Probes shorted and meter set to ohms = O.L.
3. Measuring a 1k ohm resistor = O.L.
4. Continuity setting/Diode function = O.L.

[redwire]

Re: FLUKE 179 problems

It's difficult without a schematic or knowing if the multimeter was overloaded etc.

The rotary switch wiper fingers look ok? The main PCB looks fine, some blackened copper but I do not see anything terrible.

From Fluke 179 teardown pics, the clamps are diodes (not transistors), two pairs. SMD marking code "JYc" (BAV199) or "JC" (BAL74) in OP's unit. The bridge rectifier DF06S and nearby S1B diode is the current-shunt protection.
I'm not sure what the two back-back SOT-23's "FNB9" are about.

I would do a quick diode-test on them just to make sure.


Can you check continuity between the input jack ground and the DMM ground.
By the input jack, there is SOT-23 part/cap/ferrite bead and then a skinny trace goes for a long run up to the A/D by the LED's. I'm wondering about that.
Can you read the SMD marking code of the part.

[retiredcaps]

Re: FLUKE 179 problems

Two other questions.

1. What is the input impedance of the 179 when it is set to DCV? It should be around 11.11M ohm when measured with another meter.

2. Check the serial number of the 170. If you are lucky, you might get a free replacement from Fluke if it has been recalled. See

Recalled units have a serial number below 79000000.

http://www.cpsc.gov/en/Recalls/2002/...l-Multimeters/

[retiredcaps]

Re: FLUKE 179 problems

It's difficult without a schematic or knowing if the multimeter was overloaded etc.

The predecessor to the Fluke 170 series is the Fluke 70 series IIII. There are schematics for that series and most of the input protection components and layout are similar. The main chip, lcd driver, etc are totally different though.

[retiredcaps]

Re: FLUKE 179 problems

On the Fluke 77 III service manual page 3-12, it suggests that if the meter doesn't read a 100 ohm resistor correctly, that S1 is bad, Q1, Q2 shorted, loose pins on U1, U2 and/or U1 is bad.

I would check Q1 and Q2 as already suggested. My guess is that the components marked JC3 are Q1 and Q2 by that big power resistor? There are 4 in that area so I would test them all to see if they are shorted or not.

Remember the Fluke 77 III will be similar, but not identical to 170 series as Fluke refines their design over time.

The Fluke 170 itself has gone through 3 major pcb revisions itself since it was introduced.

[retiredcaps]

Re: FLUKE 179 problems

Can you check continuity between the input jack ground and the DMM ground.

Speaking of the above, see

https://www.eevblog.com/forum/repair/fluke-179-76688/

[bwilliams60]

Re: FLUKE 179 problems

Okay here is what I have so far:
Rotary switch fingers are all good.
JC switching diodes appear to be okay but not sure on exact identification. When the single post was to the left (pin 3) and the tow were to the right (pin 2-top and 1-bot), I got the following readings:
3-1 0.00
3-2 0.618
2-3 OL
1-3 0.00
1-2 0.618
2-1 OL
which would indicate to me that 1-3 are connected and go through a diode to 2?
The S1B tests at 0.601 in forward bias and 1.084 in reverse bias
The DF06S tested as follows:
AC to + 0.556
+ to AC 1.132
AC to AC 0.002 all fuses out and battery out
AC to -ve 1.131
-ve to AC 0.553
the CFNB9 tested:
1-3 0.561
1-2 OL
2-3 OL
3-2 OL
2-1 OL
3-1 OL
The small run disappears into the mask so I cannot see where it goes.
The battery -ve to COM post measures 10.1M ohms
The small 1AM near the COM post does not test as per datasheet either:
1-2 0.673
1-3 0.00
2-3 OL
2-1 OL
3-1 0.00
3-2 0.673
That is what I have for now. Looks like some trouble there.

[redwire]

Re: FLUKE 179 problems

I don't see anything wrong with those readings

The bridge AC to AC reading is near short because the mA shunt is across it.
BAT- might have a switch transistor to VSS so 10MEG reading there may be OK.

Input jack J4 (-) must connect to PCB GND, I think.
I would check the ferrite bead is not cracked. This is right by the hoop shunt resistor. Check continuity across it, and find continuity from J4 to the PCB ground traces. PCB ground looks like an inner layer but the (-) on a few black tantalum caps should be PCB GND.

The SOT-23 marking code "1AM" by J4 I think is MMBT3904 transistor.

Does anyone know what this part does? I don't have a 77 iii service manual to look at.

I'm not sure about your pin numbering for SOT-23.
1AM might be a diode-connected transistor, so the short you see may be a B-C trace.
Next to it is a (gray) ferrite bead going to the via, to check continuity on.

[bwilliams60]

Re: FLUKE 179 problems

Well I have some good news. I started tracing the circuit from the beginning and found a bad connection between the inductor and the board. Resoldered and now everything seems to be working. I am going to compare it to a couple of other meters just to see how they compare but we are further ahead today then we were yesterday
How would one identify this inductor or put a value to it?
This is the one located very near the fuses.

[redwire]

Re: FLUKE 179 problems

That's good news to find an open circuit.

Do you mean this part? Can you measure its size. It's an oddball.
All I can find is:
Fluke 867734, Ferrite chip Inductor 95 OHMS @ 100 MHz, 3612 (9131 metric).

The part is for EMC filtering, I think added after the recall where some multimeters would crash/re-boot when leads connected to HV. Needs to be pretty low DC resistance to not upset ohms/diode-test.

I think it's actually a smaller 3312 (8531 metric) size part as the pads are farther apart.
I'd use: Wurth 74279225101 100ohms 100MHz, DCR 4mohm, 3312.