EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: Robomeds on March 21, 2014, 03:00:15 pm
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So I have a new repair project. It's a Fluke 177 meter. I've tested the AC and DC voltage and all is good. However, when I short the leads the meter reads -0.8 ohms. It seems to work well in higher ranges. When compared to my BK meter they agree to withing one count on the 177. However, they are clearly off by a lot at the very low range. I don't think the 177 was miscalibrated but I don't think it has a calibration count indicator (I could be wrong). The MOVs and diodes look good but I was wondering if one had been previously removed and perhaps put on backwards. Then again I don't think those affect resistance measurements.
Anyway, any suggestions?
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Sometime in 2012, I bought a "working" 179 and when I received it, it read -0.2ohms when shorted. :--
The previous owner was also a heavy smoker as the 179 reeked with smoke. I did the usual standard cleaning and IPA bath (twice) and the meter finally read 0.1 to 0.2 ohms.
Modemhead has listed some products he used
http://mrmodemhead.com/blog/dirty-multimeter-clean-up/ (http://mrmodemhead.com/blog/dirty-multimeter-clean-up/)
but I used gojo for the yellow parts and standard IPA for the pcb. Make sure to clean the input jacks with a qtip and IPA. Unfortunately, I was never able to get rid of the smoke smell.
I have noticed that the 17x series with firmware revision 1.x doesn't bootup saying F17x. With firmware 2.x, it boots up saying F17x where F17x denotes the model number.
edit: fixed some typos.
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That would probably make sense. This one was listed as not working and appeared to have some chemical spilled on it. I'm do another round of cleaning and see what happens.
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Well I've cleaned the board with IPA. No luck. I checked the calibration and the unit shows only one calibration. Any other suggestions?
Thanks
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Q1. Did you check the PTC? It should be around 1k ohm.
Q2. What is the DCV being sent when the 177 is in 600 ohm range mode? Is it a stable reading?
Q3. What is the current being sent when the 177 is in 600 ohm range mode? Is it a stable reading?
Q4. Check the fusible resistor. It should be around 1k ohm.
Q5. Check the MOVs. They should all read open circuit.
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Thanks, I will check those things today or perhaps Monday.
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Q1. Did you check the PTC? It should be around 1k ohm.
Q2. What is the DCV being sent when the 177 is in 600 ohm range mode? Is it a stable reading?
Q3. What is the current being sent when the 177 is in 600 ohm range mode? Is it a stable reading?
Q4. Check the fusible resistor. It should be around 1k ohm.
Q5. Check the MOVs. They should all read open circuit.
OK, I've finally had a chance to check a few things.
0. The device was only calibrated once thus we have the factory calibration (I don't think that should surprise anyone).
1. The PTC is 1.051k
2. DC voltage is 1.255V, stable
3. DC A is 312.4 uA DC, stable
4. 1.060k
5. All three are over range.
It seems the under range is only in this 600 ohm range. When I test say a 1k resistor with this meter vs a known good meter they are spot on. Only in this 600 ohm range do I see the issue. I'm starting to wonder if I don't have some small corrosion related failure.
Thoughts?
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I'll have to haul out my 175 to see if those readings are the same ballpark or not.
I'm in the middle of preparing taxes, switching from XP to some other OS and getting ready for a road trip coming up, so I won't be able to check for a few days. :scared:
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Thanks! I will be interested to hear what you find. I'm still wondering about your contamination comment. I did clean the PCB (twice) with IPA and that seemed to have ensured reliable operation but hasn't fixed the error in resistance. The small error that goes away as resistance goes up (it still reads lower than my reference meter but once I'm off the 600 ohm scale the difference shifts from a consistent .8 to something like one count lower. Seems like just a bit of current leaking somewhere.
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Isn't there any callibration pot to adjust ?
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Isn't there any callibration pot to adjust ?
None. All Fluke 17x series are closed case calibration. The offset for the 600 ohms range is stored somewhere in a chip.
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Isn't there any callibration pot to adjust ?
None. All Fluke 17x series are closed case calibration. The offset for the 600 ohms range is stored somewhere in a chip.
Damn, maybe there is an ISP port on it somewhere ?
Anyone know how to fix a multimeter if it's reading DC voltage 2x bigger than it really is ? :bullshit:
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Damn, maybe there is an ISP port on it somewhere ?
You need a lot of calibration gear to calibrate a closed case multimeter. In most cases, you cannot just calibrate one range and quit otherwise the calibration is invalid.
Anyone know how to fix a multimeter if it's reading DC voltage 2x bigger than it really is ? :bullshit:
Start a new thread on your specific problem and we can take it from there.
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I got some new info. I was messing with it and noticed a few things (most have since slipped my mind) but the big one was the current reading. Initially I thought the current readings were fine because by default the meter is in AC range and the AC ranges were fine... or at least 0 which is what you expect when you have no current applied. When I checked DC the meter shows -.5A in the mA range but 0 in the 10A and 0 in the uA range. That's at least something. Too bad Fluke doesn't release schematics anymore. Time to figure out what is in a current reading range.
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Too bad Fluke doesn't release schematics anymore.
I'm still learning how to read schematics, but I find the text based theory of operation information more valuable at this point of my knowledge level.
While there are no public schematics of the 170 series, the original Fluke 80 service manual does a good job of describing how the ohm measurement is done on the 400 ohm range. See page 2-3, section 2-8 of
http://assets.fluke.com/manuals/83_85_87smeng0500.pdf (http://assets.fluke.com/manuals/83_85_87smeng0500.pdf)
In reading section 2-8, I suggest checking
i) switch/rotary switch contacts - give them a good IPA clean
ii) give the main IC a good examination using a 10x loupe to see if you can see any contamination
iii) maybe take a dental pick or sharp probe and drag it in between the main IC or ICs to possibly dislodge something that an IPA flush cannot?
iv) check the thick film resistor for dirt/contamination and measure the value especially the 1.0001k resistor
v) check the solder joints on the COM and V jack - I remember modemhead had some issues with this
PS. What revision board is your Fluke 177? I know they have a rev 12 and 15. The two are completely different internally.
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2. DC voltage is 1.255V, stable
3. DC A is 312.4 uA DC, stable
Sorry, after a very long 2 months of stuff, I forgot about this thread and probably a lot others as well. :palm:
Anyway, using my BK5360, the Fluke 175 outputs 1.2331V and 303.1 mA when set to 600 ohm manual range.
edit: This is the only 17x I have access to nowadays.
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2. DC voltage is 1.255V, stable
3. DC A is 312.4 uA DC, stable
Sorry, after a very long 2 months of stuff, I forgot about this thread and probably a lot others as well. :palm:
Anyway, using my BK5360, the Fluke 175 outputs 1.2331V and 303.1 mA when set to 600 ohm manual range.
edit: This is the only 17x I have access to nowadays.
I'm thinking your Fluke should probably source 1 mA, not the 300 or so uA (yeah - I think you had a typo there).
Something in there may still be open circuit... especially if the output current is also low on the diode test function.
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Hey all,
Thanks for the replies. I did find something else that may be of some help. With no input on the DC mA current mode the meter reads ~ -.54mA. I might have messed up what I posted earlier because the meter defaults to AC amps, not DC like I'm used to.
Anyway, what I've been wondering is if the DC reference for the low range might have been damaged. It would explain problems with both resistance and DC amps at the same time. A big fear would be a damaged trace on one of the middle layers of the PCB (this is a 4 layer board). However, I haven't seen any visible evidence of such a problem. Would I?
Thanks all!
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I'm thinking your Fluke should probably source 1 mA, not the 300 or so uA (yeah - I think you had a typo there).
The Fluke 175 I have is rev 12 board. When I turn it on, it doesn't display the F175 at startup like the newer ones. The current manual for the 175 indicates the short circuit is less than 1.1mA.
However, since my 175 is more akin to a Fluke 77 III design, it sources 300uA (as documented in the 77 III manual).
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Re-continued from
https://www.eevblog.com/forum/testgear/fluke-187-reads-2-ohms-high/ (https://www.eevblog.com/forum/testgear/fluke-187-reads-2-ohms-high/)
For the reference of others, the 177 reads something like -0.9 ohm when shorted (auto ranging) and in the DC mA range reads a -530 mA current and, I just checked, draws 40mA from it's battery when on. The board looks good so I've been at a loss as to what is wrong. Sadly, I think it might be a short of some sort between the layers of the board but that is just a wide guess. I simply can't find any visible damage.
Depending on which pcb version of the 170 series you have, the documented battery life could be 200, 300 or 400 hours as per Fluke manuals. Assuming a 9V battery is roughly 500mAh, that would imply a 2.5mA, 1.67mA or 1.25mA draw respectively.
Does your 177 draw 0mA when it is off? See
http://www.antiqueradios.com/forums/viewtopic.php?f=8&t=264761 (http://www.antiqueradios.com/forums/viewtopic.php?f=8&t=264761)
Using 40mA when the meter is on suggests something is really wrong. What does it draw if you turn on the backlight?
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I think it was drawing ~2mA when off (I didn't have time to really verify I was getting a legit measurement). It does appear to draw current when off. Time to pull out the bench power supply to test things.
I think this is one of the earlier PCBs. It has the older style switch rotary switch vs the traces on the PCB like we see on the newer Fluke meters. I might get a chance to do some more work tonight.
Edit:
Similar to this one:
(http://217.26.67.168/uploads/3/3/3329119/fluke%20179.jpg)
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I think it was drawing ~2mA when off (I didn't have time to really verify I was getting a legit measurement).
If it draws 2mA when it is off, that implies a fresh battery will be dead in about 11 days (500/2 = 250 hours, 250/24 = roughly 10.4 days). This is just like the Mike C. meter in the antique radio forum thread.
I might have some ideas later on, but I have some research to do first.
For the ultrasonic bath, did you dunk the entire 177 into it so that it cleaned the rotary switch as well?
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I put the stripped PBC in. So everything that could be removed easily was off but the switch went into the bath. The grease on the switch was mostly washed away.
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OK, I think I'm at the bottom of this. The Fluke 642998 ASIC is bad. So with just the bare PCB I connected power and measured almost 40mA of current at 9V. The backlight ads 10mA to that. Well anything that's drawing that much current might just get warm. The 642998 was getting just a bit warm to the touch. Warm enough that I have no doubt that it is the bad part. I'm not sure if I can source a replacement.
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I'm not sure if I can source a replacement.
I recently opened an aliexpress account and got my order this week. I haven't checked my order yet to confirm the mosfets are good, but this seller sells a replacement.
http://www.aliexpress.com/store/product/642998-FLUKE-QFP/130723_1861821775.html (http://www.aliexpress.com/store/product/642998-FLUKE-QFP/130723_1861821775.html)
It is $50.76 USD for five + free shipping.
Send an email to the seller and ask if you can buy just one (1). Offer $15 USD + free shipping and the seller might do it?
I have no financial affiliation with the seller or aliexpress.
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Thanks! I found that link but didn't think to ask about getting just one chip.
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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.
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I got a $20 counter offer. I figure I will go for that. Not cheap but I really don't need 5.
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I got a $20 counter offer.
I believe it is customary to "haggle" back and forth! :-DD
Anyway, :popcorn:
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I countered, 2 for $25. :D
I'm asking for a spare just in case I screw up the first one during install! :scared:
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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?
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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)?
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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.
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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/ (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.
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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?
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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/ (https://www.eevblog.com/forum/testgear/fluke-77iv-and-179-differences-with-teardown-photos/15/)
But it appears to be conflicting.
See my response.
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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.
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More pics
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More pics
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More...
Sorry the pics aren't my best but I didn't have the right camera with me.
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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.
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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 (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.
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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
https://www.youtube.com/watch?v=qm3ZvcjiS9Y (https://www.youtube.com/watch?v=qm3ZvcjiS9Y)
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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.
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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.
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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/ (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.
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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.
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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?
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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.
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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!
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Hi, thanks but that is not the one i am looking for..