Bricked Fluke 177

[andyB2022]

Hi!
My Fluke 177 doesn't want to work any more. The idiot me just tried to measure it own current draw from it's own 9V battery via the 400mA range.... Bodged some cables around the battery connector tried to test the current, had no luck, placed back the battery and now it's dead...

I know I'm an idiot...
Do you guys know any solve for this? The microcontroller seems to work as the full display is lit while pressing the HOLD Key, PoFF and LoFF seem to work too...

Please watch the video below to better understand...
https://youtu.be/1-nA6hS6c2E

[Per Hansson]

Sorry to hear that, you can take a look at these threads, might be some valuable information in them for your case, especially the first one:

https://www.eevblog.com/forum/testgear/fluke-177-failed-and-need-support-to-repair/

https://www.eevblog.com/forum/testgear/dmm-reading-it_s-own-battery-voltage-low-voltage-detection/

https://www.eevblog.com/forum/testgear/fluke-87v-_bricked_-when-probing-own-battery/

[andyB2022]

Thank you for your tip. Looks like the DMM is pure trash.... such an expensive mistake...

[Per Hansson]

I would inspect each component with good light under  magnifying glass, if you are lucky there will be some external component that took the damage and saved the ASIC.
There was at least one example provided in the first thread.
And you know the EE mantra: tho shall measure voltages!

[andyB2022]

I've checked all regulators, I have (referenced to GND battery) 2.5V 3.3V 5V, all steady...

One thing that caught my attention was the bridge rectifier than on the AC side is open, and on DC side measures 1.7V which seems okay. (Out of circuit of course)

Also reading the first thread I can't find the -2.5V supply.

[Fungus]

I'll point people to this thread when they ask why anybody needs more than one multimeter.

[andyB2022]

So far the only questionable part I could find is this bridge rectifier which has the AC side open. After removing it from the board, the meter has no reaction to this "change". Can anyone tell me on their DMM what voltage drop does the bridge have?

Update: -2.5V rail on AD737J is present in reference to COM on the board (not battery's GND).

[tom66]

If you look at the diagram for a full bridge rectifier it will be apparent why it tests open on the 'AC' side.  There is no path for DC,  it is like a bunch of valves that reverses the connection on each mains cycle.

I think the problem is that COM on a meter is not the same as battery ground,  it is going to be floating at some midpoint reference.  Maybe 3V for instance.  Then the ADC can measure voltages above and below COM potential.

If what you did is to either short COM to battery ground, or to +9V, then it's very likely that the reference will have been damaged.

Unfortunately on many meters this reference does in fact come from the main ASIC.

[andyB2022]

So we can consider the meter dead right? Replacing the FPGA from another meter would cost as much as a new one...

[tom66]

I would wait for some others to confirm as I am not an expert in Fluke meters but I think it may be that way unfortunately.

[AVGresponding]

If you look at the diagram for a full bridge rectifier it will be apparent why it tests open on the 'AC' side.  There is no path for DC,  it is like a bunch of valves that reverses the connection on each mains cycle.

I think the problem is that COM on a meter is not the same as battery ground,  it is going to be floating at some midpoint reference.  Maybe 3V for instance.  Then the ADC can measure voltages above and below COM potential.

If what you did is to either short COM to battery ground, or to +9V, then it's very likely that the reference will have been damaged.

Unfortunately on many meters this reference does in fact come from the main ASIC.

Not sure about the 177, but on the 87, COM is 2.5V above battery -ve, as the -2.5V supply is at battery -ve. I would not be surprised if the 177 is very similar. I'm not aware of a service manual for the 177 but the one for the 87 found in those other threads might give you some pointers as to where to look.

One thing I would say about measuring your supply voltages, is don't just measure them at the regulator, measure them at the IC's they are powering too.

[Wrenches of Death]

I'll point people to this thread when they ask why anybody needs more than one multimeter.

Yep!

Sadly, this isn't the first post that I've read over the years of someone frying their meter trying to read the voltage of the internal battery.

It might be worth posting a warning about attempting to do this as a permanent sticky.

WoD

[AVGresponding]

I'll point people to this thread when they ask why anybody needs more than one multimeter.

Yep!

Sadly, this isn't the first post that I've read over the years of someone frying their meter trying to read the voltage of the internal battery.

It might be worth posting a warning about attempting to do this as a permanent sticky.

WoD

This had me wondering if there was anything specific to this in the manual; there isn't, at least in the 80-series one. The closest to it is this:

"
• Make sure the battery door is closed and
latched before operating the Meter.
• Replace the battery as soon as the
battery indicator (M) appears.
• Remove test leads from the Meter before
opening the battery door."

But this is under the general warning about avoiding shock risks etc, which I guess might lead people to think if they aren't measuring any dangerous voltages it's ok to ignore the warning.

[robert.rozee]

see the photo from this thread:
https://www.eevblog.com/forum/testgear/fluke-177-failed-and-need-support-to-repair/?all




check voltages on the pins of the 16-pin chip labelled "24351". this is the analog-to-digital converter, an LTC2435-1:
https://www.analog.com/media/en/technical-documentation/data-sheets/24351fc.pdf

with the F177 set to DC VOLTS, input leads shorted, and using pins 14, 15, 16 as your ground point, you should see:
3.3v on pin 2 (supply for the ADC)
2.5v on pin 3 (reference voltage)
0.0v between pins 5 and 6 (in+ and in-)

report back the voltages returned, as well as what is on the F177's LCD.


cheers,
rob   :-)

[andyB2022]

You mean shorting COM and Voltage plugs on the DMM and then doing those measurements? Meter set to V DC or mV DC?  Will try the measurements and come back with some updates.

In my opinion, if it was a problem with the ADC, the meter would work normally just it won't be able to measure anything correctly...but it doesn't even want to "cycle" to different measurement options when I spin the dial.

Also if you guys have an ideea of what IC I can remove from the PCB and then test the meter without it, I'll try it... nothing to lose right now...

Regardless of the screen, it's still the same as in the video of the first post. Wherever the dial is set it will stay in continuity mode and will beep sometimes randomly like it would detect a dead short on a PCB / wire etc.

If anyone can tell me the input impedance of their meter between V and COM? I measure 2.5M ohms with a crappy UNI-t...

[tooki]

So we can consider the meter dead right? Replacing the FPGA from another meter would cost as much as a new one...

ASIC, not FPGA. An FPGA is a very different type of device.

[andyB2022]

Thanks for pointing out, my bad 

[andyB2022]

report back the voltages returned, as well as what is on the F177's LCD.

With input leads shorted (V and COM) we have:
Pin 2   4.962V
Pin 3   2.5V
Pin 5   2.5V
Pin 6   2.5V

All measurements referenced to pin 14,15,16 of the ADC.

[andyB2022]

Small update, I've tried to measure all possible things on the board and mark them on a photo. All measurements in white font are referenced to the GND marked with the Bright Green circle in the middle. V and COM on the multimeter input jack were shorted during this measurement as one of you guys suggested above.

Measurements with the orange line pointing at the values with white background and orange text are referenced to bright green GND too.

On AD737 I took the two -Vs +Vs measurements against it's 8'th pin which should be GND according to the datasheet. As you can see here I've noticed something really strange in +Vs side, a fluctuation between 2.459 - 4.95V.

After other measurements around the board I came back to this AD737 and the fluctuation was gone.... steady 2.459V

Hope the pic will help you guys better understand...

[alonsojar]

Hello, my 175 (I assume is the same meter except the lack of led light) in DC position shows 11M Ohms between V and Com measured with a 87v.
Good luck !!

J. Alonso

[AVGresponding]

Do you have access to an oscilloscope? It might be instructive to observe whether there is activity on the ADC pins 12 and 13. It doesn't matter about decoding it, just seeing if there is activity there or not would be useful.

[BeBuLamar]

I hope you get it fixed. I have a 175 that needs new case as the built in yellow hoslter is a mess.

[andyB2022]

Here are the DSO captures for :LTC2435

As far as I know about SPI, SCK signal doesn't look good...(pin 13)

[andyB2022]

Better shots on this one
Yellow is SDO pin 12
Blue is SCK pin 13

[AVGresponding]

Well, it looks as though the ADC is alive and outputting something. Is the signal path to the Fluke ASIC intact?