EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: mdogsa on October 10, 2015, 03:31:56 pm
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Now I'm there too. My Fluke 189 died during measurements! Exactly on switch over from mA to V (DC). Display just turned off and that was it. :wtf:
I was doing some low voltage measurements of a Li-Ion charger. It's completely non-responsive now. Never before had problems with it.
Of course I opened the housing checked all the connections between batteries and pcb, mode selector and so on. I tried it also with lab power supply. I than made a detailed check of the pcb all the way from batteries over the switch mode power supply to processor ic, display ic, checked components... Voltages are there, display dead... Crystals also oscillate. The dedicated chips are a big problem because there is no info on them. I just hope that the processor didn't die...
I'm still suspecting the switch mode power supply. Voltage values are little strange. Can somebody please with a functioning 189 meter check the component marked in red and also the voltages on secondary caps (meter turned on) marked with yellow circles on the attached picture?
I'd need also a photo of the mode selector knob - because of the contacts orientation. Two of them jumped out on disassembly and I'm not 100% shure how they were assembled.
Did anyone experience similar problems with a FLUKE?
Thanks.
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Exactly on switch over from mA to V (DC). Display just turned off and that was it. :wtf:
Were the multimeter probes still in series with circuit when you switch from mA to VDC?
Voltages are there, display dead.
Do you see any voltages on the lcd pads?
I'm still suspecting the switch mode power supply. Voltage values are little strange.
What readings are you getting that seem strange? Are they rock solid or fluctuating?
I'd need also a photo of the mode selector knob - because of the contacts orientation. Two of them jumped out on disassembly and I'm not 100% shure how they were assembled.
Selector knob photo at modemhead's Fluke 189 clean up photo gallery.
http://mrmodemhead.com/blog/gallery/fluke-189-clean-up/ (http://mrmodemhead.com/blog/gallery/fluke-189-clean-up/)
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-The probes were disconnected on switch over.
-I didn't measured on the LCD pads yet. Will try it.
- Voltages on the secondary of the switch mode supply were like 5.7V and 3.2V. They aren't fluctuating. I looked further on the circuit and there are also two linear regulators for 3.3V and 5.2V. This voltages are spot on. There is also a 5V rail which is also ok. Maybe I was wrong regarding this matter.
Looks like that on Monday I'll get access to another fluke 189 from a colleague. I'll than have a chance to make some comparison.
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The component in red circle is an inductor.
Voltages aftes SMPS and before voltage regulator should be +5.5V and -5.5V, and after voltage regulator +5 and -5V.
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From top to bottom looking at picture, left to right
-3.13
-5.74
-3.13
-3.13
-5.17
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Thank you all for your support.
Indeed the component is an inductor and the voltages are as xwarp wrote. I get the same values on mine. My colleague brought today his meter and I made a comparison. On his the values are also the same. So, the power supply works ok. I also tested the LCD screen which is also ok. I also removed the supercap because it's not in the best condition.
I also tried the optical connection with a PC computer. It doesn't work. So my suspicion regarding a CPU fault maybe right...
I'm also thinking about what turns the meter on? Or better how is it turned on? Because with inserted batteries there is always power on the board. When you turn the mode selector to a range there has to be a signal to the CPU which turns it on from standby or similar?
To be continued...
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Not sure if this is of anything, but once I had a very weird issue with my Fluke 187.
One time while left on resistance and not measuring anything (probes not contacting anything), switched to voltage then suddenly the display went off.
Turned it off then onto one of the measurements, got nothing, tried this a few times but still got no display.
I figured it was the batteries so replaced with new ones and noted contacts were clean and contacts were touching the batteries. Ouch same thing, no display.
I was about to open it up to inspect the circuit but decided I should first use a magnifier to visually inspect the battery contacts again - they were super clean, no rust no dirt.
Placed the batteries back in and turned the switch, I was surprised it came alive!
I'm still puzzled about that.
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I investigated the problem with my FLUKE a little further. Especially the turn on procedure.
Looks like when you turn the meter on with the mode selector signals go from the selector over the 74HC04 HEX inverter. Left upper part of the PCB seen from behind. So far so good. Hex inverter works. From there the signals go to the CPU, display chip...
But I have maybe a problem on the pin 4. It's one of the inverted outputs. There is a track from this pin under the inverter which goes to a via which is also a blind via I think. I tried to track down where this signal goes. With no luck. I tried every single pin on the PCB and simply couldn't find it.
I'd really appreciate it when somebody could check it on a working 189. Maybe I have a broken track in one of the middle layers...
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This track goes to 1MOhm resistor that is located under the lcd (top left of the pcb).
(http://s13.postimg.org/hda3h0yjn/189.jpg) (http://postimg.org/image/hda3h0yjn/)
Sorry for the poor quality of the picture.
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Thanks for that. Unfortunately I can't test it because I sent the meter to a FLUKE service.
And guess what..the meter is still under warranty!
It's now on the way to Netherlands, to Eindhoven where the FLUKE Europe headquarters are.
We'll see.
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A quick update on the repair of the meter. Warranty was still valid so I got a brand new current produced model the 289! ;D I couldn't believed it when they called me. Very impressed of FLUKE and their service.
But unfortunately I'll newer know what was wrong with my old 189...
Thank you all for your support.
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I realize this is an old thread but it may be used for reference.
I had the same issue described in the previous comment: Fluke 189 worked perfectly. No drop or other culprit. Tore it down. Inspected everything. Battery compartment contacts slightly corroded so I cleaned them up.
On second inspection of the board the brass contact patches where the metal points from the battery compartment interface with the board appeared dull. I lightly scored the contact patches to reveal bright metal.
On reassembly the meter returned to full functionality. The issue was power and non-conductivity due to what I assume was oxidation on the contact patches.
Hope this helps somebody.