Multimeter repair time again! Fluke 177, reads -.8 ohms

[Robomeds]

Thanks!  I found that link but didn't think to ask about getting just one chip. 

[retiredcaps]

Thanks!  I found that link but didn't think to ask about getting just one chip.

A lot of sellers on ebay and aliexpress are super flexible when asked for custom orders.  They would rather have your business than to lose it to someone else.

Additionally the Fluke IC is a speciality item.  Other than a handful of people, most would not attempt this repair deeming it not worthwhile and simply buy a new meter.

If that seller won't do a custom order, I see others selling the same Fluke IC so you can ask another.

Let us know what happens.

[Robomeds]

I got a $20 counter offer.  I figure I will go for that.  Not cheap but I really don't need 5. 

[retiredcaps]

I got a $20 counter offer.

I believe it is customary to "haggle" back and forth! 

Anyway, 

[Robomeds]

I countered, 2 for $25. 

I'm asking for a spare just in case I screw up the first one during install! 

[Robomeds]

OK, more updates.  I have the new Fluke ASIC installed.  The meter now gives good readings in all non-current ranges when compared to a Bryman/Amprobe AM270 we have in the lab.  Basically all readings agree to about 3 counts.  I haven't checked the AC values, I can do that later.  My current issue is the current measurements are still off.  The DC mA range reads with a ~.64 mA offset.  I'm pretty sure that would correspond to a .64 volt offset somewhere in the system.  Note this offset occurs when the system has an open circuit.  When the offset is accounted for the mA readings agree with the Amprobe within a few counts.  The A range currently shows zero current regardless of applied current.  I know current is flowing since I had the other meter in series. 

New suggestions?

[retiredcaps]

The DC mA range reads with a ~.64 mA offset.

1) Did you do another ultrasonic bath after you replaced the Fluke IC?

The A range currently shows zero current regardless of applied current.in series. 

I hate to ask the obvious, but

2) Is your 10A fuse good?
3) Did you remember to press the yellow button to get into DC A mode?  The 17x series defaults to AC A.

4) Is the current draw with the replacement IC now drawing around 2mA (vs 40 mA for the defective one)?

[Robomeds]

The DC mA range reads with a ~.64 mA offset.

1) Did you do another ultrasonic bath after you replaced the Fluke IC?

The A range currently shows zero current regardless of applied current.in series. 

I hate to ask the obvious, but

2) Is your 10A fuse good?
3) Did you remember to press the yellow button to get into DC A mode?  The 17x series defaults to AC A.

4) Is the current draw with the replacement IC now drawing around 2mA (vs 40 mA for the defective one)?

So to go down the list:
1.  Yes, I did give the thing a bath once I was done. 
2.  That is a valid question but in this case I was actually testing with the meter open and bypassing the fuses.  I was sending the current in series through the Amprobe and was seeing current on it (and from the power supply) but not on the Fluke. 
3.  Yes
4.  I checked the current draw and was seeing 3-4mA depending on mode.  If the current draw is supposed to be 2mA then we seem to have a leaking component or perhaps a short inside the board layers.  Any suggestions for finding it? 

I do have one more of the ICs if the one I just replaced was bad.  I kind of doubt that is the issue.

[Robomeds]

OK, well in the 179 thread we have some current draw information:
https://www.eevblog.com/forum/testgear/fluke-77iv-and-179-differences-with-teardown-photos/15/

But it appears to be conflicting.  So the measured consumption is around 1.5mA but bigsky noted that the rated battery life is 200 hours out of, presumably, a 600mAh battery.  So a draw of 3 mA gives you the 200 hours.  I'm seeing 3.5-4 or so.  I could believe that the newer version of the meter (mine is something like PCB rev 10) has less current draw than the older one.  Still, 3.5-4 vs 3 is still over.  I'm still feeling like something is drawing a big more current than it should. 

[retiredcaps]

2.  That is a valid question but in this case I was actually testing with the meter open and bypassing the fuses.  I was sending the current in series through the Amprobe and was seeing current on it (and from the power supply) but not on the Fluke. 

I can't quite picture what you are doing, but I trust you when you say it is 0.

4.  I checked the current draw and was seeing 3-4mA depending on mode.

It is higher than what I expect.  See why in following post.

I do have one more of the ICs if the one I just replaced was bad.  I kind of doubt that is the issue.

While it is possible the replacement IC is bad, I would not change it until other things are checked.

5) Do you remember if the original IC worked with current measurements?

6) Can you post a clear focused picture of your pcb, front and back so we know exactly which revision we are looking at?

[retiredcaps]

OK, well in the 179 thread we have some current draw information:
https://www.eevblog.com/forum/testgear/fluke-77iv-and-179-differences-with-teardown-photos/15/

But it appears to be conflicting.

See my response.

[Robomeds]

2.  That is a valid question but in this case I was actually testing with the meter open and bypassing the fuses.  I was sending the current in series through the Amprobe and was seeing current on it (and from the power supply) but not on the Fluke. 

I can't quite picture what you are doing, but I trust you when you say it is 0.

4.  I checked the current draw and was seeing 3-4mA depending on mode.

It is higher than what I expect.  See why in following post.

I do have one more of the ICs if the one I just replaced was bad.  I kind of doubt that is the issue.

While it is possible the replacement IC is bad, I would not change it until other things are checked.

5) Do you remember if the original IC worked with current measurements?

6) Can you post a clear focused picture of your pcb, front and back so we know exactly which revision we are looking at?

2./5.  Basically I was connecting the two meters in series so they both would measure the same current flow.  I took the fuses out of the Fluke and was using jumpers instead (a long winded way of saying this isn't fuse related).  The mA ranges agree with the exception of the offset.  This is similar to the failure I used to see except previously the offset was larger.  I don't actually recall if the A range was working in the past.  I know it read zero reliably while the mA range didn't even when the inputs were shorted.  However, I don't recall if I actually tested it for non-zero readings.  I think I would have but honestly I just don't recall right now.  The mA range in the past did work but it had the very large offset (-500mA in the mA range vs 6mA now). 

4.  I agree the 3-4mA seems a bit higher than expected.  However, this is a rev 10 board so it would makes sense that it's higher than the newer board. 

[Robomeds]

More pics

[Robomeds]

More pics

[Robomeds]

More...
Sorry the pics aren't my best but I didn't have the right camera with me.

[retiredcaps]

2./5.  Basically I was connecting the two meters in series so they both would measure the same current flow.

Yes, after I went to sleep last night, I understood what you meant.

I don't actually recall if the A range was working in the past.

Hmm, too bad. We don't know if the problem is the new IC or a failure somewhere on the pcb trace.

I have a couple of ideas, but need to do some research first (at least a couple of hours).  It will take a couple of days as I have some other stuff I need to get done first.

[bigsky]

Hi, let me chip in - the 200 hour life was from the Fluke website - http://www.fluke.com/fluke/uken/digital-multimeters/fluke-170.htm?PID=56027 - but retiredcaps says it's for an older version of the meter and other docs now say 400 hours. 3-4mA seems reasonable for a rev 10 with ASIC.

It would be useful to do some tests to find out the minimum battery voltage for these meters and compare that to the battery discharge curves.

[retiredcaps]

It would be useful to do some tests to find out the minimum battery voltage for these meters and compare that to the battery discharge curves.

Martin did a video and noted around 5.5V using an external power supply.  Starts around 11:15

[bigsky]

That's interesting given that I measured the output voltage on most of the ohms ranges at 7.3V. Wonder what happens when the battery voltage is less than that.

[retiredcaps]

The DC mA range reads with a ~.64 mA offset.  I'm pretty sure that would correspond to a .64 volt offset somewhere in the system.  Note this offset occurs when the system has an open circuit.

For the 0.64mA offset, let's try the following

1) Put a Fluke 87V into DC mV mode.
2) Turn on Fluke 177 and put it into DC mA mode.  It should show 0.64.
3) Use the Fluke 87V to measure the voltage drop across the 1 ohm, 2.5W resistor, just left on the 10M input divider, in the 177.
4) If it is 0.0mV, then the problem with the 0.64 offset might be due to calibration?
5) If it is 0.64mV, then I'm not sure where the problem is right now.

[retiredcaps]

The A range currently shows zero current regardless of applied current.  I know current is flowing since I had the other meter in series.

Ideas, suggestions.

1) Since your Fluke 177 is a bit older, see if it being recalled by Fluke. Recalled units have a serial number below 79000000.

http://www.cpsc.gov/en/Recalls/2002/CPSC-Fluke-Corp-Announce-Recall-of-Digital-Multimeters/

Though you are not the original owner, Fluke may want to get the meter and repair/replace it regardless due to safety/liability.  At worst, they can so no, at best you get a brand new calibrated Fluke 177 for the cost of sending them the meter via USPS ($10 USD).

2) There are no schematics for the 170 series.  However, since the analog IC is a 60 pin IC, there may be similarities between this and the older models?

A quick brief look shows the following analog ICs are quite similar in functionality which might give a clue to the analog IC in the 170.

From the schematics and service manuals.

Fluke 75 II - analog IC part number 683052
FLuke 77 III - analog IC part number 791269
Fluke 27 - analog IC part number 700112

Despite serveral years and generations the above 3 analog ICs have similar pinout mappings.

3) If the 170 analog IC is similar, then we can look at the Fluke 77 III analog IC schematics.   This may or may not prove anything because the schematics may not be applicable.

What we are trying to find out is if pin 24 (AM0) is the 10A input.  If yes, it should show some number > 0 when there is amps flowing through the meter.

[Robomeds]

The DC mA range reads with a ~.64 mA offset.  I'm pretty sure that would correspond to a .64 volt offset somewhere in the system.  Note this offset occurs when the system has an open circuit.

For the 0.64mA offset, let's try the following

1) Put a Fluke 87V into DC mV mode.
2) Turn on Fluke 177 and put it into DC mA mode.  It should show 0.64.
3) Use the Fluke 87V to measure the voltage drop across the 1 ohm, 2.5W resistor, just left on the 10M input divider, in the 177.
4) If it is 0.0mV, then the problem with the 0.64 offset might be due to calibration?
5) If it is 0.64mV, then I'm not sure where the problem is right now.

I'm reading 0.6mV across COM-mA terminals when the meter is in the mA range.  Interestingly it goes up to 1.6mV when I change to the A range BUT still measure across the mA-COM terminals.  In diode check I see 1.7mV when the 177 is in various voltage check ranges and 1.8 in the ohm check range.  One more note, in mA range the 87V reads -.6mV while in the other ranges it reads positive.  Switching to the mA range results in about a 2.4mV shift.  Also, AC vs DC mA doesn't impact the reading.

Other info:  Yes, the meter is within the recall range.  SN 788....  I had no idea about the recall but will ask.  I'll try to look at the pinouts tomorrow as it's getting late (assuming Fluke doesn't just say return it). 

Thanks for all the info so far!  A replacement certainly would be the "best" solution but I actually like the idea of learning what's wrong and fixing it.

[retiredcaps]

Other info:  Yes, the meter is within the recall range.  SN 788....  I had no idea about the recall but will ask.

Make sure to refer to the link I posted.  New Fluke customer support people may not know about it?

[retiredcaps]

Just for closure on this thread, Robomeds informed me that Fluke sent him a new 179 177 due to his unit being a recalled unit even though he wasn't the original owner.  So Fluke did the "right thing" by taking the recalled unit out of the field and probably destroyed/recycled it.  I doubt they even bothered to try fixing it.

[Robomeds]

Yes, sorry I forgot the update.  The turn around time was about 6 weeks (it was around the holidays).  Also, I to clarify they sent me a replacement 177, not 179.  Since I'm not the original owner I suspect this was sent out due to the safety related nature of the recall.

Big thumbs up for Fluke!