Fluke 179 teardown photos

[rsjsouza]

I tried to find a Fluke 170 series teardown on the web without success, therefore I took some pictures of my Fluke 179 to show its guts... Quite remarkable construction I must say!

Battery compartment. Usual build in several Flukes, but for the price I would have preferred to see brass inserts instead of self-tapping.


Front cover removed. Absolutely fantastic the molded insulation on the rotary switch and surrounding the fuses, leads and battery.


Front view in detail. Note the rotary switch markings and the depth of the holes that house the front button PCB contacts. You cant ask for much more protection...


Back cover with the circuitry removed. Notice the hole for the cal probe (left), shielding and the buzzer.


Rotary switch. Pretty cool the small tip to aid the switch alignment.


LCD and front buttons. The LCD housing is incredibly tough and fitted. The button contacts are different than the typical "opposing forks" design found everywhere else. Not sure how better this is, but maybe the contact area is larger...


Fuses and test lead inputs. If you are like me, at first glance it seems the battery is too close to the ground PCB track, but a few pictures above you can see the cover has a plastic insulation between the two. Ahhhhh... I can sleep in peace!


Bottom side of the fuses and test lead inputs. Large tracks, solid connection to the shielding (the hole on the right) and the only interesting thing I found was the tiny track that crosses between the two pads on the left. Low clearance, maybe?


Bottom side of the digital circuit. The large round thing is the cal button and one can see the quality of the PCB and routing.


(horrible picture). Removing the plastic white cover. The molded plastic circuit cover also uses self-tapping screws. Not a big fan.


This is the bottom side of the rotary switch without the plastic cover. Notice the large ground plane and the interesting tinned ring surrounding two of the five pins of a device.


The molded plastic with the mounted LCD. Not everybody can claim their equipment has such nice level of finishing...


Back side of the LCD display with the zebra contacts. This assembly is incredibly tight (four screws on the corners guarantee that).


The top side of the PCB. Impeccable component selection and solderings.


Digital section. Two backlight LEDs, two custom parts from LT, one AD737 (TRMS-DC converter) and one "off-the-shelf" MSP430F437.


Input protection, battery clip, rotary switch and the (foil?) resistor under the black plastic cover.


The other side, showing the rectifier bridge, the shunt resistor and the two fuse holders (the 11A fuse is in place). I have no idea what is the square copper under the DALE resistor. Calibration point or assembly PCB orientation maybe?


Enjoy! 

[alm]

Fuses and test lead inputs. If you are like me, at first glance it seems the battery is too close to the ground PCB track, but a few pictures above you can see the cover has a plastic insulation between the two. Ahhhhh... I can sleep in peace!

I assume the responsible Fluke engineer didn't lose any sleep over it, since the negative lead from the battery connector is most likely directly connected to circuit ground and the common input terminal. Unless you spotted an isolated DC-DC converter somewhere...

[rsjsouza]

I assume the responsible Fluke engineer didn't lose any sleep over it, since the negative lead from the battery connector is most likely directly connected to circuit ground and the common input terminal. Unless you spotted an isolated DC-DC converter somewhere...

Considering the battery compartment is completely isolated from the rest of the circuit using molded plastic, I am pretty sure that someone lost some time thinking about this design choice. I personally don't like to see the battery too close to the input terminals in several other multimeters as any high-voltage surge could cause a spark and either ruin the battery or inflict an overvoltage to the equipment (the battery casing is not connected to the negative terminal).

[anotherlin]

Really nice teardown !
I own a 179 but I don't want to open it.

[rsjsouza]

Really nice teardown !
I own a 179 but I don't want to open it.

Merci beaucoup; before I purchased mine I found mjlorton's excellent reviews below, but he stopped the teardown just after removing the outside plastic case (I would have done the same; it was a loaner). Thus I hope this helps others have a deeper insight on this excellent DMM.

[Fox]

Just a quick notice the LT Part with the 24351 marking is actually
an of the shelf LTC2435 24Bit Sigma-Delta Analog to Digital Converter.
The tiny part LTPZ is an LT1790 Voltage reference.
The marking under the Dale resistor is a alignment markfor the different layers to align.
Hope this pieces of information helps.

[Monkeh]

Please, use thumbnails or resize your images.

[rsjsouza]

Just a quick notice the LT Part with the 24351 marking is actually
an of the shelf LTC2435 24Bit Sigma-Delta Analog to Digital Converter.
The tiny part LTPZ is an LT1790 Voltage reference.
The marking under the Dale resistor is a alignment markfor the different layers to align.
Hope this pieces of information helps.

Thanks for the info! I confess I didn't lose too much time in identifying the other part after I read "Fluke" in one of them... My mistake.

Please, use thumbnails or resize your images.

I understand that large images may be annoying as you don't have the full picture in the screen, but I wanted to be sure that all details were there... (sometimes JPEG resizing algorithms are a bitch to details). Also, I find them easy to navigate using the keyboard arrows...
Obviously they could be resized to 1280x900 (weird camera resolution) to fit on the screen, but I can't deal with thumbnails.

[OZ1LQO]

Nice pictures, is that SOT-23 component next to the GND post the internal temperature sensor?
I would make sense as the 77IV doesn't have it mounted and it doesn't have the thermometer (thermocouple) option.

cheers

[AVGresponding]

Fuses and test lead inputs. If you are like me, at first glance it seems the battery is too close to the ground PCB track, but a few pictures above you can see the cover has a plastic insulation between the two. Ahhhhh... I can sleep in peace!

I assume the responsible Fluke engineer didn't lose any sleep over it, since the negative lead from the battery connector is most likely directly connected to circuit ground and the common input terminal. Unless you spotted an isolated DC-DC converter somewhere...

Battery negative is NOT connected to the Common input, it is about -2.5V wrt Common. This is why trying to measure its own battery voltage will kill the meter.

[Gyro]

Note that this is a bumped 2013 thread.

[AVGresponding]

Note that this is a bumped 2013 thread.

You have something against necrophilia?   

[techneut]

 

[Gyro]

Note that this is a bumped 2013 thread.

You have something against necrophilia?   

Well, err yes. It's a sick and illegal perversion.

With regard to the thread, it's often uesful to insert a note to inform people that they may be getting into things that were resolved a decade ago rather than the specific question from the person who bumped the thread.

@OZ1LQO, I'm afraid I don't know the answer to your question but I'm sure somebody here does. I'm not sure if the Fluke 179 is one of their meters that has a publicly available service manual / schematic. It looks as if it isn't...  https://eevblog.com/forum/repair/service-manual-fluke-179/


EDIT: Looking closer at the photos, it does look as if it is temperature sensing the Common jack, it's hard to think what else would need to go down there. There is a single thin bottom side track that leads from it up to the 'works' of the meter (it runs a bit close the the Volts jack and PTC surge resistor pin for my liking).

[AVGresponding]

Note that this is a bumped 2013 thread.

You have something against necrophilia?   

Well, err yes. It's a sick and illegal perversion.

With regard to the thread, it's often uesful to insert a note to inform people that they may be getting into things that were resolved a decade ago rather than the specific question from the person who bumped the thread.

@OZ1LQO, I'm afraid I don't know the answer to your question but I'm sure somebody here does. I'm not sure if the Fluke 179 is one of their meters that has a publicly available service manual / schematic. It looks as if it isn't...  https://eevblog.com/forum/repair/service-manual-fluke-179/


EDIT: Looking closer at the photos, it does look as if it is temperature sensing the Common jack, it's hard to think what else would need to go down there. There is a single thin bottom side track that leads from it up to the 'works' of the meter (it runs a bit close the the Volts jack and PTC surge resistor pin for my liking).

Close. It's part of the thermocouple compensation network. Here's the description from the 87V service manual, on the equivalent in that model:

"Temperature
The V/Ohms input is connected the same as in mVDC to FE_O (U1 pin 19) with the
exception that U1 provides a gain of 10 to the signal. Another measurement of the
temperature of the input terminals where the thermocouple wire transitions to copper is
required to calculate the actual temperature sensed by a thermocouple. Since U1 is
controlled by the microprocessor, this measurement is done by routing two different
values of current from the U1 current source via RJT_I (U1 pin 35) to Q3 and the
resulting VBE is routed, buffered and passed to the FE_O (U1 pin 19) ready for
measurement. The reference junction temperature is calculated from these
measurements. Inductor L2 and capacitor C2 keep noise out of the measurement
circuitry. Since thermocouples are easily broken and give incorrect readings, a periodic
test of the thermocouple is required. A current from the U1 current source is routed to
ISRC (U1 pin36) and on to the thermocouple that is connected from V/Ohms to
COMMON. The resulting voltage drop across the thermocouple is connected to the U1
internal comparators and converted to a digital signal at COMP_O (U1 pin 24) ready for
evaluation by the microprocessor. "

Here's the relevant part of the circuit diagram:

[Gyro]

Yes sorry, (thermocouple) compensation is what I meant by temperature measurement.

Useful info.

[OZ1LQO]

Thanks! To you and 'AVGresponding'