Fluke 189 Help Needed - Page 1
Forum section: electronics / beginners

author: aueloxdad
author_rank: Newbie
timestamp: February 02, 2024, 09:00:48 pm
content: I have a gently used Fluke 189 that I just recently wanted to test a 24VAC relay and was surprised by the lack of voltage reading. Fuses are good, MOV's are open PTC @1.1kohm's. It will read DC voltage, resistance and will read Hz. Any thoughts? Thanks in advance.

author: bdunham7
author_rank: Super Contributor
timestamp: February 02, 2024, 09:05:56 pm
content: Can you measure some other AC source, perhaps mains voltage? I take it the issue is that it reads near zero volts on the AC range?

author: aueloxdad
author_rank: Newbie
timestamp: February 02, 2024, 09:42:02 pm
content: I have checked on a 120 volt circuit as well. Just the "open leads" indication.

author: bdunham7
author_rank: Super Contributor
timestamp: February 02, 2024, 10:13:24 pm
content: Quote from: aueloxdad on February 02, 2024, 09:42:02 pmWhoa, wait a minute--what does that mean? Does it give you a value near zero with a hundred or so counts of noise in the last few digits--or does it say "LEAdS" ?

author: BeBuLamar
author_rank: Super Contributor
timestamp: February 02, 2024, 10:13:50 pm
content: Open Lead you meant OL? In that case try manual ranging by pressing the range button a few time. If it works then somehow the autoranging doesn't work.

author: aueloxdad
author_rank: Newbie
timestamp: February 03, 2024, 03:34:56 pm
content: "OL" is correct. Changing from auto range to manual has no effect.

author: bdunham7
author_rank: Super Contributor
timestamp: February 03, 2024, 04:48:06 pm
content: OK, so if you put it in the VAC mode--the first detent after "OFF", with the leads disconnected (or not installed) you get "OL" (which means overload, not open leads) on the display? How about if you short the inputs with a banana cable or by shorting the two test leads together--what does it read then?

author: aueloxdad
author_rank: Newbie
timestamp: February 03, 2024, 08:58:38 pm
content: With the leads disconnected "OL" and with the leads connected and shorted "OL".

author: bdunham7
author_rank: Super Contributor
timestamp: February 03, 2024, 10:47:39 pm
content: That's bad. I don't have a Fluke 189 schematic and can't find a good, clear picture of the board, but if you are going to troubleshoot further you should find the TRMS converter chip. I don't know which one it uses, but you can just look up each of the chips on the board until you find the one that is a TRMS converter. Then measure the input and output of that chip to see what is going on there.

author: BeBuLamar
author_rank: Super Contributor
timestamp: February 03, 2024, 11:56:55 pm
content: Just curious does it behave the same with the ACV as the ACmV?

author: aueloxdad
author_rank: Newbie
timestamp: February 04, 2024, 01:10:02 am
content: Yes it does.

author: mwb1100
author_rank: Frequent Contributor
timestamp: February 04, 2024, 02:21:28 am
content: There are a couple of (non-Fluke) documents that written up in Chinese for diagnosing and repairing some problems with 187/189 multimeters in this thread:-https://www.eevblog.com/forum/repair/fluke-187189-repair/msg3205856/#msg3205856That particular post has the documents that have been auto-translated from Chinese to English. The auto translation is dicey and can be hard to follow, but you might be able to get some ideas for areas to look at.The one thing I could get from the first document (page 20) regarding AC reading problems is to visually check the custom Fluke 669918 chip which apparently handles the voltage and TRMS calculations. The document says if that chip is bad the only repair is to replace it with a chip from another 187/189. I have no idea how you'd check out that chip more completely if it looks OK visually. The 669918 chip also handles the DCV measurement (all measurements?), so if DCV is working I think it's likely not a problem with that chip.The second document points out several points where the voltage can be measured to see make sure the power to various function blocks is OK.

author: aueloxdad
author_rank: Newbie
timestamp: February 04, 2024, 02:27:48 am
content: Thank you for your response and time.

author: bdunham7
author_rank: Super Contributor
timestamp: February 04, 2024, 02:32:47 am
content: Quote from: mwb1100 on February 04, 2024, 02:21:28 amI wouldn't have thought that they would (or could) put a high-performance TRMS converter on their custom chip, but just disassembled mine and could not find any external TRMS converter. So I guess that's that, unfortunately.

author: Eraldo
author_rank: Regular Contributor
timestamp: February 04, 2024, 10:32:01 am
content: This multimeter can measure ac in 2 different modes: one in its own ac range switch and the other in the dc switch when pressing the blue button (ac+dc measurement) try measuring in this mode if it shows any value.Then if it doesn't work you might want to check the white capacitor (near the movs and power resistors) to see if it works. Try measuring its capacitance with a multimeter or a simple transistor tester. Im not sure if you can get any meaningful value testing in-circuit in this case but give it a try.There shouldn't be many things to go wrong in the ac if the dc works fine. Just to make sure measure some of the protection circuitry components and the fusible resistor.Maybe I'm paranoid but definetly make sure the rotary switch contacts are intact and are in the correct orientation (check out some teardown images/videos) and make sure there are 4 of them.Also test out the Ac milvolt range just to make sure. I believe it doesn't share the same path as the Vac and you can find out if the true rms converter works. You could generate a small signal with a function generator of even an arduino(make sure signal is smaller than 5v and test it with another dmm)

author: aueloxdad
author_rank: Newbie
timestamp: February 06, 2024, 06:39:54 pm
content: I will test it and get back to you. Thanks

author: Eraldo
author_rank: Regular Contributor
timestamp: February 07, 2024, 06:05:02 pm
content: Some of the things i said above are a bit over the top and not all of them specific for your problem so i wanted to sum it up with this second post to be more clear and add some other things1. Check all the basic ranges of the multimeters to see if any other range is broken/not working (Vac mvAc Vdc mvDc ohm currect ac current dc. Basic checks would suffice.2. Check the mV AC range to see if the rms converter is fine. Even better if you check the current AC range since you'll be sure it goes directly to the rms converter instead of the voltage path which might be the thing compromised in this case3. If these ac ranges work fine then you might need to check the main path of the ac line which is the same one as the dc one but instead of going straight to the resistor network (after passing throu the protection) ,it passes through a capacitor first.Check that capacitor whith another miltimeter by either measuring it's resistance, or better, try measuring it's capacitance. If you have another meter with capacitance measurement, try measuring it. The capacitor is a white package, as big as the protection resistors, which is found near the protection circuitry.4. If all of them are ok then you might need to do some deep digging by yourself, testing the protection components etc....5. This one is just a precaution but make sure you don't lose the contacts of the rotary switch when opening the multimeter.Post pictures and other findings here and we'll help