Fluke 374 True RMS Clamp Meter

[softwarejedimaster]

Hello all,

I have a Fluke 374 clamp meter that when powered on displays the "374" then 4 dashes at boot time, then the display does not change.  Normally after the "374" it goes to whatever mode you have selected and shows 0.0 in the display.  This one only shows the 4 dashes and the (>30volt) lightning bolt warning icon on startup and never goes to the zero screen for the mode I have selected.  All switch positions exhibit the same behavior and don't change when making a rotary dial selection.  All pushbuttons seem to function ok in that they beep the correct pattern or turn the backlight on when pressed.  These buttons are "inrush", "min/max", and backlight respectively.  Based on this alone the micro seems to be alive and doing things.  Since no schematics exist for this fluke yet, I am left guessing and testing.

I have done a general pcb inspection for visually damaged parts and probed around the various multiplexers and op-amps and they seem to have their power rails satisfied.  I guess I'm left to signal tracing unless anyone else here has witnessed this type of behavior in the 37x line of these Fluke meters.

I have top-side and bottom-side pcb pics for your viewing pleasure!


Any thoughts or suggestions will be greatly appreciated.

[retiredcaps]

I have a Fluke 374 clamp meter that when powered on displays the "374" then 4 dashes at boot time, then the display does not change.

Just curious, where do you get all these broken Fluke meters?  Your 787 had no continuity beep, your 1507 couldn't turn off.  Are these work meters or ebay "as is" purchases?  Or have you had this much bad luck with Fluke products?

I have done a general pcb inspection for visually damaged parts and probed around the various multiplexers and op-amps and they seem to have their power rails satisfied.  I guess I'm left to signal tracing unless anyone else here has witnessed this type of behavior in the 37x line of these Fluke meters.

This sounds like another potential broken via like your 787 and modemhead's blog below (see Epilog section)

http://mrmodemhead.com/blog/fluke-77-iv-copper-corrosion/

One thing that might help is to take the pictures again, but with bright sunlight behind the pcb so you can trace out the circuit.  I did a picture like this in the following thread

https://www.eevblog.com/forum/repair/uei-dm393-repair-advice-all-segments-on-all-the-time/

You can also try taking macro shots of the pcb and then viewing them on your computer monitor rather than squinting at the pcb.

Post these pictures and maybe we can spot something.  Right now, I have a couple of other ideas that I have to think about before communicating them.

PS. My UEI DM393 is still broken.  It is in the "fix later" pile if I get a scope.

[retiredcaps]

BTW, on the pcb, it says Fluke 2010 and the white serial number sticker says SN 8413060306.  If this serial number matches the outside of the case, then this 374 is not being recalled as per

http://www.fluke.com/fluke/caen/support/safety/37x-recall

However, the white serial number is 10 digits while the outside serial number is 8 digits which leads me to believe the 10 digit serial number is probably for the pcb only.

== snip ==

January, 2013
Dear Fluke Customer:
Fluke is voluntarily recalling certain 373, 374, 375 and 376 Digital Clamp Meters that were manufactured between September 1, 2010 and October 31, 2012. The models and serial numbers affected are listed in the table below.

Fluke-374
Manufacture Dates Oct 2010 – Feb 2011   
Starting Serial No. 14270001
Ending Serial No. 16079999

== snip ==

[softwarejedimaster]

Already checked the s/n. It is not part of the recall.  It is the outside case serial that detrrmines the true vintage.  PCB serial numbers are used only by fluke and not its customers when it comes to recall notices.  This recall had to do with the socket connections to the PCB.  Mine have the shake proof washers and locktite.  As I mentioned in earlier posts, im not tying to get these units replaced or repaired by fluke.  I have this weird obsession with buying broken flukes and repairing/restoring them to their former glory.  So far i have about a dozen or do that have been repaired and restored.  My lab is getting cluttered with them so I will be forced to start selling them to make more room for new broken ones!!!

[retiredcaps]

I have this weird obsession with buying broken flukes and repairing/restoring them to their former glory.

As you can tell, some of us do the same, but due to the low CDN $ and USPS significantly raising their International shipping prices (> 70%), I have had to resort to virtual repairs like this one.

In  modemhead's blog article that I mentioned earlier, I found this contribution by Bob in the comments section that may provide a hint to the ---- (4 dash) problem?  You should read the entire comments to get context.

Bob Grieb says:
January 20, 2016 at 8:41 pm
Hi Again, I found the problem with the dashes on the display. The main chip feeds 3.3V to a resistor divider, and the selector switch selects one of the taps to pick a range and feeds it back to the chip. The trace that was connecting the voltage to the top of the divider was toast, so the chip was always getting 0V as the selection voltage, which is probably not a valid range selection.

[retiredcaps]

BTW, I would love to see pictures of what you have repaired and more importantly, what you did to fix them.  It doesn't have to be an elaborate write up. Even a quick note on what was wrong would be interesting.

[retiredcaps]

If Bob's insights are applicable to the Fluke 374, I wonder if the area around the selector switch and resistors R36, R37, R38, R39, R45 and R54 warrant a closer look/testing?  Check the vias, traces, etc.

I think they are marked "01C" or 10k ohm?

[softwarejedimaster]

I was meaning to capture videos on my YouTube channel but I was more obsessed with doing electronics  troubleshooting rather than posting videos of my repairs.  I see now that decision was wrong.  I should have been documenting these repairs so that others can enjoy these repairs as I enjoy doing  them. I don't have all the details on the various Flukes I have processed to date but I will put something together for the great folks like retiredcaps and modemhead, who obviously are great resources and have a lot of experience in this area.  I hope to post something in the upcoming weeks once I compile some coherent account of my last couple of years of work in this area.

Cheers to all.

[retiredcaps]

My lab is getting cluttered with them do I will be forced to start selling them to make more room for new broken ones!!!

You have a long way to go. See

https://www.eevblog.com/forum/chat/anyone-want-to-challenge-excavatoree-and-his-staircase-photo-with-24-fluke-27s/?all

[retiredcaps]

I was meaning to capture videos on my YouTube channel

What is the link to your channel?  Searching for "softwarejedimaster" on youtube yields nothing and adding spaces in between brings up what you expect given the success of The Force Awakens.

[retiredcaps]

I think they are marked "01C" or 10k ohm?

BTW, six 10k ohm resistors is what the Fluke 80 series I used for their code switching as per

http://mrmodemhead.com/blog/fluke-83-dmm-repair/