Fluke 185 Review

[shakalnokturn]

How much of a full performance check have you made? Enough to see that ACV measurements are no good, anything else?
In your situation I'd start by swapping the suspicious EEPROM for a copy of one of the dumps provided here, at least with that you should be able to find out if the ACV being wrong is due to a lost calibration or hardware fault.

[ErnestB]

Hi. Thanks for replying. The DCV is within the +/-0.05% compared to HP3478A. Frequency measurement is correct. I will check the resistance mode. I do not think it just "lost" the calibration data from the EEPROM, but I don't rule out anything yet. The meter was several years in the annual calibration program and one year they couldn't calibrated it anymore (they don't gave the specifics about the fail). That's why the meter ended up as a hobby project. I have ordered the meter and was only used by me all the time. Regarding the AC voltage being out of the specifications I see a clear strong frequency dependant behavior so first I suspect one of the capacitors, or a RC combination. Resistors being more stable over the time and could easily being measured, and even have clear value marking on it. As the capacitors doesn't makes it more difficult without the parts list. Now I will try different C values to try to understand better what it does. As I can see on the block diagram it should be some kind of high pass filter or better compensation network. But I suspect they did some part of the compensation with hardware and some in the firmware. That would be a bummer as I can not do the calibration. If I put a random cal data in it I do not expect much accuracy, and still can not calibrate the damn thing.

[ErnestB]

Did some testing but still don't know what is causing this systematic AC Voltage reading error. There are a lot compensating capacitors, for every range a few, but I think that chance that all of them are wrong is very low. There must be one main source of error. The main AC couple capacitor C72 is common for all ranges, but if I short circuit that one not much change. Then we have the serial combination of C99 and C100, that are maybe also used for all ranges. These could be the source of common error for all (tested) ranges.

[maxniz]

hi,
i friend gave me an'185 .. it is a bit inaccurate but above all when I measure a voltage it takes 20 seconds for a correct indication. it rises very slowly and stops at the end showing the more or less correct value and this for any measure and on any scale. it makes me think that there is an altered resistance but I have no diagram and no values..can someone help me thanks

[shakalnokturn]

That sounds typical of PCB contamination. Any signs of battery leakage such as deposit or corrosion on the battery terminals?

[maxniz]

no.... it looks new... the battery are  in a separate compartment ..clean compartiment.

[DrMr]

Hi, all,
do hope this thread is still alive, I would like to join conversation on Fluke 183 /185 (TX 1 & 3)!
I am (formaly!) newbee on this site, joined it few days ago!
The reason is problem I have with my Fluke 183!
This istrument I bought as new 20+ years ago, and have been using it for more than 10 years, being very satisfied with it, it was joy using it!
And, then he became partialy defective, and put out of use because new instrument replaced it!
Now, I have found it forgoten on shelf, and decided to try to bring it back to use, if possible!
So much of introduction, let me explain problem:
Instrument measures perfect voltage and current including frequency, but not at all resistance / capacitance, continuity / diode / 50 ohm range!
On these measurements he is just randomly shoving some values, or even behaving as being leads short circuited on diode / continuity / 50 ohm range!
I have measured test voltage on the leads while being on some of these measurments, and it seems there is (almost) no voltage at all, meaning there is no constant current flowing at all, or it is very low!
This to say because sometimes it seems that instrument recognises short circuited leads, for example, when he ask to make short on 50 ohm range, or being on continuity range, showing 0 or some milivolts!
Indicative for this problem is also that he newer shows on these measurements 0L when being at open leads!
Meanwhile I have checked as well photo MOS relays, which by my knowledge have function at these ranges, and they seems to me OK!
At least they are changing output side when input diode is being activated!
My PCB is Fluke 185 - 3001 REV 003  , it seem that difference between 183 and 185 models was mainly in firmware, beside mechanical possition on range switch!
Only strange behavior I have noticed, while testing it by internal tests, is that button MIN / MAX shows value 99 instead 01!
Is it same on other units or is it real fault on my instrument?
I would appreciate any help from you, guys, and would also thank you all for help provided on this forum!

[ErnestB]

Hi. I don't know if you have further worked on your instrument in the meantime and maybe you have solved it? I read that for those measurements the instrument uses current source. Maybe to search in that direction. Time ago I was trying to solve the AC deviation that I have on my Fluke 185. You can see the short explanation about the current source in the photo few comments before this one.

[ErnestB]

After a long period my 185 was in the 'multimeter-drawer', I took it out once again to think about this problem of his. I have done some measurements again to help think about it. In conclusion: The DC voltages are 'spot on' regardless the range used. Different values tested.
The AC voltage is the problem. I see a clear and strong deviation 1) from a correct value, 2) depends on the range, 3) have some 'strange' frequency behavior.
In general:
1) On the 0.5 and 5V range the values are about 6 to 7% lower then they should be (compared with 87V and Siglent oscilloscope Vrms).
2) On the 50V range the values are about 1.5 to 2.5% higher then they should be (compared with 87V and Siglent oscilloscope Vrms).
For the points 1) and 2) regardless if I use 100Hz or 1kHz.
3) The measured value goes up with the range.
4) On the ranges 5 and 50V, when increasing the frequency, I see a clear drop in value up to about 5kHz and then stabilize up to 20kHz, and then (as expected drop).

Mine line of thinking, if a specific range switch is not functioning right, that should have influence also on the DC reading (same range switch I suppose?), unless the problem in the range switch would be frequency dependent and not DC.
Strange that (for example at the range 5VAC) the voltage first goes down with the frequency, but only up to about 5-6kHz, and then stays flat up to 20kHz!

Does anybody has any clue? In what direction to look? TIA

I have added the spreadsheet for some details. Regarding the added pic/graph, from the sheet, the measured value with a good 87V was 3.78Vrms (not much freq. dependent).

[ErnestB]

Does somebody knows what components are doing the range switching? Photo MOS relay Nais-Panasonic V238AD01, that big regular relay and/or the 'switcher IC' TC1109? I can not find any datasheet either...
Edit: I have done test on the AC current (uA and mA range), and that seems all okay compared to a few trusty meters!