Fluke 287 inaccuracy in upper 50k Ω range - Page 1
Forum section: electronics / testgear

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 04, 2025, 04:33:42 pm
content: Hi everyone, i just got a secondhand fluke 287 (because I'm still a student with limit budget) but i found out that the upper 50k Ω range show significantly wrong when compared to the others i got is Aneng Q1, Apech AC-286 (although it's purpose is a current clamp) and color in the resistor that i had (some is ± 1 and ± 5%, i don't have precision resistor).here is the data i got in case of attachments can't be load properly :My question is that does calibration help to make it becomes accuracy? Or because the hardware is corrupted?(I'm so sorry this is my first post therefore maybe i have some typo, wrong grammar and very little experience in this field)

author: Fungus
author_rank: Super Contributor
timestamp: April 04, 2025, 05:14:06 pm
content: Show some example readings... what's the error?

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 04, 2025, 05:16:30 pm
content: It measured value is too big when comparing to the others multimeter

author: Fungus
author_rank: Super Contributor
timestamp: April 04, 2025, 07:32:34 pm
content: Quote from: Els_Chaos on April 04, 2025, 05:16:30 pmHow big?

author: tooki
author_rank: Super Contributor
timestamp: April 04, 2025, 07:49:57 pm
content: Quote from: Fungus on April 04, 2025, 07:32:34 pmAre you not seeing the screenshot embedded right in the original post?!?If it's not appearing for you, use the Quote button to see the original post's source code so you can get the URL.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 05, 2025, 08:26:39 am
content: You might want to open the case and see if the supercap has leaked, or if there's any evidence of battery leakage.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 05, 2025, 09:36:30 am
content: The supercap is a little bit old, may i need to replace it?

author: Fungus
author_rank: Super Contributor
timestamp: April 05, 2025, 10:15:52 am
content: Quote from: tooki on April 04, 2025, 07:49:57 pmNo.

author: tom66
author_rank: Super Contributor
timestamp: April 05, 2025, 12:00:00 pm
content: Reuploading the screenshot for the OP. It's hosted on Imgur embedded which some adblockers don't allow.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 05, 2025, 03:27:00 pm
content: Quote from: Els_Chaos on April 05, 2025, 09:36:30 amIt's certainly something to be aware of. They are easily available, and not expensive, but if they leak and it isn't cleaned up, it can cause damage

author: Fungus
author_rank: Super Contributor
timestamp: April 06, 2025, 09:34:45 am
content: 68k, 100k, 300k are all on the same range (50k-500k).4.7M is a different range (500k to 5M)What does it say for a 470k resistor? What does it say for a 680k resistor?

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 07, 2025, 08:33:16 am
content: for 680k ± 1% resistor it came up with the reading of 715.9kΩ. for 470k ± 1%, the result is 495.3 kΩ

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 07, 2025, 08:34:16 am
content: could i get its part number please

author: AVGresponding
author_rank: Super Contributor
timestamp: April 07, 2025, 10:40:28 am
content: Quote from: Els_Chaos on April 07, 2025, 08:34:16 amhttps://www.eevblog.com/forum/repair/fluke-289-super-capacitor/

author: Ugur
author_rank: Regular Contributor
timestamp: April 07, 2025, 03:00:02 pm
content: Varistors at the input may also be a problem.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 08, 2025, 02:03:47 pm
content: the 287 has a lifetime warranty do does Fluke covers the supercap?

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 08, 2025, 02:12:01 pm
content: Excuse me, how can i check if them is still good sir

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 08, 2025, 02:14:15 pm
content: Here is the image of that capacitor. It seems like that there is some enroded oxide around the cap.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 08, 2025, 02:23:03 pm
content: I measured the resistance between 2 legs of each RV (the blue one). 2 of them showed open circuit but 1 (nearest 10A shunt resistor) showed up 18.89M ohm. Is it bad?

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 08, 2025, 02:38:40 pm
content: I just made a measurement with aneng q1. The value of measured component is written in the image. The OC stands for open circuit

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 08, 2025, 03:20:21 pm
content: I would contact Fluke and have them repair it for free. Fluke never asks you to prove where you bought the meter. Oh I didn't realize that you're in Vietnam.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 08, 2025, 03:37:23 pm
content: It is a little bit hard for me in Vietnam. Although it actually has retailer in vietnam but i dont know will they accept repair a 2nd one

author: bdunham7
author_rank: Super Contributor
timestamp: April 08, 2025, 03:58:47 pm
content: A couple of observations for you:1) You can simply remove the super cap and clean the board area around it. The meter will be nearly fully functional (only some memory/RTC functions use it) and you will be able to do all of your tests and work without replacing it.2) Your erroneous resistance measurements are high, not low. Input protection MOVs and other components cannot be the cause of high readings, only low.3) The accuracy of meters is not that good at high resistances, from 5M to 50M it is 1.5%, from 50M to 100M it is 3% and above 100M it is 8%.The first things to check when you have an issue like this are the test current and compliance voltage. So take another DMM that has a 10M input impedance, connect the two together and set the 287 to resistance and the other to volts and then to current. See if those output voltages match up to what is shown in the manual. High resistance readings only in the upper parts of the range is a pretty strange symptom, IDK offhand what would cause that.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 08, 2025, 04:35:46 pm
content: do i need to bring this to calibrating service sir? As i read some posts in EEVBlog, they said that the Varistor should show Open circui and could you tell me more clearly how to check if the resistance measuring is good sir.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 08, 2025, 05:45:27 pm
content: Quote from: Els_Chaos on April 08, 2025, 02:38:40 pmThe two that measure 1k are good; that's what they should. RV1 should measure OC like the RV2 and RV3. It connects across system GND and the guard traces, and is in series with RV2 and RV3 from the VΩ jack.I suspect there's some contamination on the board. Give it a good clean, and measure it again. If it still is measureable, unsolder it and measure again. If it's measurable, then it needs replacing. If it ins't, once out of the board, then the board still needs cleaning some more...

author: bdunham7
author_rank: Super Contributor
timestamp: April 08, 2025, 05:54:58 pm
content: Quote from: Els_Chaos on April 08, 2025, 04:35:46 pmCalibration isn't likely to fix this and will likely just be an unnecessary expense. Don't calibrate a broken meter!I don't know what repair services are available to you or at what cost, but instruments like this are generally not economical to repair unless you manage to do it yourself--or have a friend. I agree with earlier comments that contamination of the board is a possible issue, but I'm hard pressed to explain exactly how and why it would cause your symptoms. However, a good cleaning would be a reasonable place to start.

author: mwb1100
author_rank: Frequent Contributor
timestamp: April 08, 2025, 07:18:34 pm
content: As part of your clean you might want to soak the PCB in 99% isopropyl alcohol (IPA). I had a problem with my Fluke 187 giving very wonky readings in the high Ohms range (your problem sounds different though). A 24 hour soak followed by a 24 hour dry with a small fan fixed the problem. My understanding is that the IPA soak 'absorbs' moisture that might be causing some problems. I've only ever heard of this moisture thing being a problem with the fluke 187/189 series, but if you have everything apart anyway...Just remember to remove anything that might be damaged by the soak such as fuses, which I forgot to remove, and the screen.-Fluke 187 "seeks" in high Ohms ranges

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 08, 2025, 07:29:49 pm
content: Quote from: mwb1100 on April 08, 2025, 07:18:34 pmAfter your success I fixed my 189 with the problem that with the leads disconnected the meter never shows OL in resistance reading. It shows something like 250 megaohms. After the treatment it works perfectly. However the OP meter reads too high instead of too low so I doubt that it's the same problem.

author: Fungus
author_rank: Super Contributor
timestamp: April 08, 2025, 08:19:58 pm
content: Quote from: Els_Chaos on April 08, 2025, 04:35:46 pmTry removing the supercap first. It looks bad.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 10, 2025, 04:10:56 pm
content: i tried using other function like diode and it showed the value completely different from aneng q1. I test a good diode, aneng q1 read the forward voltage as 0.158V but the fluke 287 read short circuit 0.078V.

author: bdunham7
author_rank: Super Contributor
timestamp: April 10, 2025, 04:13:05 pm
content: Quote from: Els_Chaos on April 10, 2025, 04:10:56 pmDifferent meters will show different results for diodes if they use different test currents. However, both of those numbers look off for a regular diode.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 10, 2025, 04:37:34 pm
content: it is a high frequecy low drop-off voltage diode using in smps, its part number is MBR30100

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 10, 2025, 04:38:28 pm
content: i only have 100% IPA solutions only. Do i need to mix it down to 99% sir.

author: Gyro
author_rank: Super Contributor
timestamp: April 10, 2025, 04:57:21 pm
content: People say 99% because it is very hard to get 100%.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 10, 2025, 04:59:40 pm
content: I already tear it down. What i need to do next sir. Prepare a small box and fill IPA into it then let the entire pcb soak in IPA, doesn't it sir. i already discharged all capacitor in the pcb.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 10, 2025, 05:03:24 pm
content: I have to compare reading of my 287 with others and see what I have. I rarely ever measure anything more than 50kOhms.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 10, 2025, 05:16:37 pm
content: actually i need a reference for my reading in case of extra accuracy so that i bought this fluke(((

author: bdunham7
author_rank: Super Contributor
timestamp: April 10, 2025, 05:18:37 pm
content: Quote from: Els_Chaos on April 10, 2025, 04:37:34 pmThat's not a "normal" diode at all, it is an ultra-fast recovery Schottky and will give you some pretty strange readings, although IDK about 0.078V.You can soak it in 100% IPA if you have it, use a very soft brush (like a watercolor paintbrush) to clean it a few times. Then bake it at a low temperature (50-60C) for a few hours.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 10, 2025, 05:37:56 pm
content: How can i bake it sir? I only have a hair dryer and sunshine 🥺 but maybe expose them under the sun is not a good idea

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 10, 2025, 06:33:42 pm
content: Quote from: Els_Chaos on April 10, 2025, 05:37:56 pmI understand that in Vietnam few people have oven but he meant using an ordinary kitchen oven which is very common in the US and Europe but not in Vietnam. It's too bad too that you're in Vietnam because I have sent several 287's to Fluke for repair under warranty and they never questioned where I bought them or when I bought them.

author: mwb1100
author_rank: Frequent Contributor
timestamp: April 10, 2025, 07:07:05 pm
content: Quote from: Els_Chaos on April 10, 2025, 05:37:56 pmWhen I did my 187 I put a small fan (on low speed) blowing on it for 12 or 24 hours. But keep in mind your problem's symptoms are different than mine. I can't remember if I removed the selector or not when I did the IPA dunk. If you decide to do that (others here might chime in on whether it's a good idea or not), make sure you take photos so when you reassemble it everything goes back in the right place and position. And make sure you don't lose any of the spring contacts - it might be difficult to purchase replacements.As I understand it, the main point of the IPA dunk is to remove any moisture that might be trapped in some nooks and crannies. I wouldn't have thought that a 187 (or 287) would be so sensitive to that, but what do I know? Only that I was surprised when the IPA dunk solved my problem.And as others have already mentioned, 100% IPA is great. I think anything down to about 90% is probably OK - main thing is to avoid the 60-70% that you get at the grocery or pharmacy.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 10, 2025, 11:42:31 pm
content: I checked the 287 against the Fluke 45 and the readings are quite close. I used all 1% resistor.Resistor 287 4568k 68.39k 68.32k100k 99.94k 99.91k330k 330.85k 331.13k1M 1.005M 1.005MSo my results that they are very close.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 11, 2025, 04:37:32 am
content: After soaking them and dry under the hair dryer in low power mode, i measured the VR1 and it still show 18Meg. I check all relative components according to schematic and they were still fine. All value in accepting range.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 11, 2025, 05:22:55 am
content: I'd try pulling VR1 out and measuring it. Or at least lifting one leg; it'll tell you whether the reading is the component or the board.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 15, 2025, 04:52:00 am
content: The problem is much worse than i thought. After removing the RV1, it still show 18Meg. Looking at the schematic i cant find out which components have possibility to fail.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 15, 2025, 05:04:52 am
content: May I ask, how long did you soak it in the IPA bath for?

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 15, 2025, 05:08:53 am
content: I think that, according to the schematic, there is some problem with rotary switch that can cause leakage? Because the input section is isolated by the switch only

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 15, 2025, 05:12:43 am
content: I soak it for about 1h30' and dry it under hair dryer for 1h

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 15, 2025, 05:17:12 am
content: Maybe should i soak it for much longer like 1 day or 2 days sir

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 15, 2025, 11:34:21 am
content: I soaked my 189 for 24hours and dried for almost a day. However, my meter was reading low. It reads 240megaohms or so without anything. The OP meter reads high so I don't think it's the problem.

author: bdunham7
author_rank: Super Contributor
timestamp: April 15, 2025, 01:25:54 pm
content: Quote from: Els_Chaos on April 15, 2025, 04:52:00 amThat 18M reading may not be an issue at all and may be normal. Or perhaps it points you in a different direction--the guard circuits near the main ASIC.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 15, 2025, 01:47:10 pm
content: I don't know but I am thinking if the OP meter has problem with only certain ranges then possible the constant current for those ranges are too high?

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 15, 2025, 01:58:01 pm
content: Yes, that is sir. My multimeter show significant error at ohm range, diode range only. The others like current, mV, V, capacitor, continuous is still fine.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 15, 2025, 02:23:14 pm
content: But not all ohm ranges are bad. Only the higher range. I know that the meter puts out a constant current and measures the voltage to display the resistance. This current is different for different ranges. So it's possible some of the current level is too high. I don't remember but back when I measured it I think it uses about 3 different current levels.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 15, 2025, 02:51:33 pm
content: I just attached the schematic of fluke 189 which is similar to fluke 287. According to page 45, i can see that there is a square box which the current source is inside. Adn as (mr) bdunham7 said there is GRD3 trace which connect VR1 to series of resistor which values is around 9Meg so the rest must be somewhere.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 15, 2025, 03:37:44 pm
content: Oh the 189II is the same as the 287 I think. I don't have that one. I have to original 189 and the 287 and 289 but not the 189II. By the way are you Vietnamese? I am too but I lived in the US for almost 50 years now.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 15, 2025, 03:43:08 pm
content: Yes sir, i'm still a student in HCMUT (Ho Chi Minh University of Technology), my major is electronics

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 15, 2025, 03:46:52 pm
content: My hypothesis is that there is maybe some problems with the Fluke SL10327PBF, a customed ic. If so, i have no ways to fix iti can't find out replacement part.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 15, 2025, 04:18:53 pm
content: I think Fluke offers the limited lifetime warranty in Vietnam too. Perhaps try to contact them and see what they say. I have sent 3 287 to Fluke for repair under warranty. They didn't ask for proof of purchase. Just the serial number.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 15, 2025, 04:29:39 pm
content: But i dont know that they will charge me for repair, won't they?

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 15, 2025, 04:38:17 pm
content: But actually i broken the seal and will they accept that

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 15, 2025, 06:36:19 pm
content: I wouldn't know but if there is a contact number or email address I would contact them and ask. It doesn't hurt.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 16, 2025, 05:27:35 am
content: Quote from: BeBuLamar on April 15, 2025, 03:37:44 pmClose; 187II = 287, 189II = 289. The manual is for the AN version

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 16, 2025, 06:02:07 am
content: is there any hope to repair this VOM

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 16, 2025, 08:31:35 am
content: They replied back and require me to send them the proof of buying, name of the seller which i bought this VOM, the date of buying. However, i bought it from 2nd market so it is impossible to send them those.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 16, 2025, 10:17:06 am
content: There isalwayshope

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 16, 2025, 11:55:31 am
content: According to these symptoms, may i need to replace fluke customed ic?

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 16, 2025, 01:02:46 pm
content: Quote from: Els_Chaos on April 16, 2025, 08:31:35 amOK that's bad news. I guess because it's the policy in Vietnam. Over here in the USA they didn't ask me anything except for the serial number. For those like the 287 with limited lifetime warranty they just fix it. For those with only 1 year warranty they check the manufactured date and if it's less than 1 year I wouldn't have to supply them proof of purchase. If it's more than 1 year then I would have to prove the date I bought it.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 16, 2025, 01:09:38 pm
content: It is a little bit unlucky for mee, i just want to repair it as not have enough budget to buy a new one. I spent scholarship to buy it 🥹😭😢

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 16, 2025, 03:14:50 pm
content: Quote from: Els_Chaos on April 16, 2025, 01:09:38 pmYes I hope you can have it fixed. I used to live in Cu Xa Lu Gia near your school. My older sister went to the college of civil engineering there (cong chanh).

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 16, 2025, 03:53:27 pm
content: i hope soo, still figure out which part can be damaged

author: AVGresponding
author_rank: Super Contributor
timestamp: April 17, 2025, 05:25:52 am
content: It's easter long weekend here, so after I get home from work today I'll have a good look at the schematics and pull my 289 apart for some measurements

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 17, 2025, 07:34:51 am
content: Oh, do you have a 287 model sirr? Could you measure the resistance between 2 legs of VR1 in a good VOM one for reference sir

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 17, 2025, 08:23:18 am
content: I just assembled it back and check for the current source and find out that there are 3 source, the first is 1mA for under 1kohm range, 100uA for upper range and under 50k and 0uA for above 50k. But 0uA is really suspicious, my Aneng Q1 spec, it can measure up to 1uA resolution.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 17, 2025, 09:33:16 am
content: Quote from: Els_Chaos on April 17, 2025, 07:34:51 amThe 287 and 289 are almost the same, I should be able to get some meaningful measurements for you.The front ends should be identical afaik

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 17, 2025, 10:01:24 am
content: Quote from: Els_Chaos on April 17, 2025, 08:23:18 amYour meter has the problem with over 50K ranges but how can it measure with 0uA? Has to have some current right?

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 17, 2025, 01:13:18 pm
content: Yes, i think so. I connect a proble of fluke 287 in serie with a current meter in uA mode and the reading show nothing. Or my multimeter cant measure under 1uA range like 100pA or so

author: bdunham7
author_rank: Super Contributor
timestamp: April 17, 2025, 01:45:18 pm
content: It should be 10µA for the 50k range which you should be able to measure. You had some errors on this range? Then 1µA for 500k and 5M, 0.3µA for 50M and 500M.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 17, 2025, 01:59:30 pm
content: Yesd that is sir. I measured a 68k resistor and the amp meter show nothing but the value is read 70k ohm

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 17, 2025, 02:03:43 pm
content: I just use my 287 to measure a 1M resistor and measure the current with the Fluke 45 and the current is 1 microamp.

author: bdunham7
author_rank: Super Contributor
timestamp: April 17, 2025, 02:28:10 pm
content: Quote from: Els_Chaos on April 17, 2025, 01:59:30 pmYour Aneng meter probably shows zero for all values close to zero below a certain threshold.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 17, 2025, 02:33:24 pm
content: could you test with 50k range sir

author: bdunham7
author_rank: Super Contributor
timestamp: April 17, 2025, 02:49:58 pm
content: What you want to know is whether the current stays the same throughout the range, right?So I get about 10µA on the 50k range and 1µA on the 500k range into a short (just the current meter). Then using a 47k and 470k resistor respectively I get the same currents. So the design for these ranges is constant current through the entire range. I think the top two ranges--50M and 500M--do not work this way but I don't have resistors handy to test those.Edit: Actually I do, just not at the top of those ranges. On the 50M and 500M ranges I get ~346nA into a short. With a 10M resistor on the 50M range I get ~182nA and with a 100M resistor on the 500M range I get ~36nA. I believe the way those two highest ranges work is they put a 10M resistor across the output (in parallel with the resistor being tested) and then calculate the resistance from the result. The manual does not go into this AFAIK, but that is the way some other meters work and the math works out here.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 17, 2025, 03:02:47 pm
content: I measure a 15K which makes it goes to 50K range and the current is 10microAmpI measure a 100K which makes it goes to 500k range and the current is 1microAmp

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 17, 2025, 03:18:48 pm
content: maybe tomorrow i need to contact my teacher to borrow a better multimeter and recheck the current of range 50k - 500k

author: AVGresponding
author_rank: Super Contributor
timestamp: April 17, 2025, 05:41:19 pm
content: I get the expected currents with my 289. As has been noted, it's unlikely the Aneng meter can provide a meaningful reading at such low currents.It might be worth checking the current source components; is the area clean? Are there any signs of damage? Do the resistors (R71, R72, R173) measure correctly? Or somewhere close, you might not get a super accurate reading in-circuit. If they read lower in-circuit, they're probably ok, if they read higher, they are probably bad. Does Q13 get a drive signal and turn on and off?It's worth checking the clamps (CR4, Q7, Q8) (CR3, Q4, Q6) for contamination/damage as well.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 18, 2025, 04:28:35 pm
content: Thank you very much. Here is my result. Unit is Volt.For Vclamp section:- Both Q4 & Q7 which is NPN transistor came up these values : Vbe = 0.5; Veb = 2.7 ; Vbc = 0.5; Vcb = 1.5; Vce = 0.6; Vec = 2.4. I dont think these values is typical for a npn transistor? As its Veb and Vcb should be 0 as it is reversed biased.- Both Q8 and Q6 showed up: Vbe = 0; Veb = 0.6; Vbc = 0; Vcb = 0.6; Vce = 2; Vec = ? (the multimeter behaved like charging a capacitor).- Both dual diode CR4 and CR3 have forward voltage of 0.7. But there is problem with CR4 and CR3 as when i change my probe order, it showed reversed voltage around 2.2V (Cathode - Anode voltage) which the CR19 (has the same model) didn't face up with.For current source section:- All the value is correct with respect to the schematic, the N-channel mosfet is still good. The capacitor C17 and C14 didn't show short circuit.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 18, 2025, 06:29:02 pm
content: When you say you are getting 0 for Vbeand Vbcon Q6 and Q8, do you mean you are getting a diode voltage drop reading of 0V, or do you mean they are open circuit/over range readings?

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 19, 2025, 01:26:17 am
content: I mean diode drop voltage sir

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 19, 2025, 04:47:52 pm
content: I just checked resistor divider, the resistance between the 1st and 7th pin is about 18meg, close enough to the resistance between VR1. However in the schematic, it doesn't have 1st pin

author: bdunham7
author_rank: Super Contributor
timestamp: April 19, 2025, 05:07:28 pm
content: Quote from: Els_Chaos on April 19, 2025, 04:47:52 pmI assume you are using the 189II/AN schematic which is the only one I know of that is available. Keep in mind that it is not impossible that there could be slight differences between the schematic and your instrument. However, I'm assuming you have the early revision 287 and I'm not aware of any discrepancies that anyone has found yet.Your resistor assembly Z2 does have a pin 1 and 2, they are up to the left of the area where the lower divider resistors (pins 3-7) are. The resistor assembly itself should have 10M between pins 1 and 2 but no continuity between the remaining pins. Therefore if you are measuring 18M, 10M is from pins 1-2, 1.1M is from pins 3-7 and the remaining 7M or so is coming from some other circuit component. IDK if this is normal or not, perhaps someone with an early 287 or 289 could check for you.

author: mqsaharan
author_rank: Regular Contributor
timestamp: April 19, 2025, 05:49:16 pm
content: Hi Els_Chaos,Following are a few comments/suggestions from a noob. So, please take them with a grain of salt. I hope I have not made too many mistakes in my reply.First of all, what I have understood from your posts is that your meter has seen some high voltage spike and most probably while it was in its ohms function. I guess, the pulse was not high enough otherwise the MOVs would have been toast but it was long enough that it has damaged the MOV(s).If you are comfortable with soldering through hole and SMD components, then hopefully, it will be easy to diagnose/repair it.My first suggestion is to remove all three MOVs until you diagnose the problem. In order to check if these as well as your new ones are OK, I would suggest you to find someone with an insulation resistance tester. And check those MOVs at 500V setting. The reading should be close to 100 MegaOhnms at least, higher is better. The general MOVs available are 560 volts, I guess. They should work, too.It is not very clear from some of your posts what you have tested and what the results are.What AVGresponding has asked you is to check the clamps whether they are shorted or not. From your reply, at least, I couldn't figure out if they are shorted or not because I don't know the meaning of zero reading on your meter in diode function.If you can, I would suggest you to simply desolder 4 transistors namely, Q4, Q6, Q7 and Q8, check them out of circuit, then check the Resistance function as described below and then reinstall them only if they are OK. After removing these transistors, you can confidently check the diodes CR3 and CR4 in-circuit.One important thing to note is that my suggestion to remove MOVs and transistors is because they are protection components. They don't affect meters functions unless they are damaged by themselves, then they'll screw up the readings.You might be right that the front end chip is toast. Or at least its current generating part is.The front end chip is SL10327 with "FLUKE" markings and part number 2103969. Interestingly, this chip has the same markings with same number of pins as in Fluke 17x series and 87V meters. There might be differences in internal circuitry. I don't know. Or they all may be the same chip.In order to check the resistive voltage divider (ceramic resistor network) and the front end chip, at least its switching part and ADC, do as follows:1. Connect your Aneng meter in Diode mode or a AA/AAA 1.5v cell to 287.2. Select V function on 287. It should read the Open Circuit voltage of Aneng or the cell.3. Now, press Range button. It should lock on the 5v or whatever range it is in.4. Note down the reading.5. Press the Range button again. The meter should switch to 50V range. It'll drop the Least Significant Digit but the reading should be the same with or without 1 digit variation in the new LSD.6. Repeat step 5 again and note that there shouldn't be any gross change in the reading in next higher range.If the readings remain the same, it means both your resistive divider and front end chip, well, at least its input switches, ADC and other main functions are OK.You can use the same way to check the Ohms function, too. The good thing with this approach is you don't need another meter to verify the readings. One important thing here is you need to use some kind of clips to hold the resistor and don't touch your finger(s) with probes.Start with, say 33 or 47 ohm resistor, Keep pressing the range button and check the reading. It should not change.For higher ranges, use, say 1k or 10k or 100k resistors.Now, If you see the wrong readings in the higher ranges as you have mentioned many times, then obviously there is something wrong with either the front end chip or some other circuitry.In case, you finally decide that the front end chip is bad, may be you can source it from within your country or China or from someone who has broken 287/289.Please note that changing this chip will render your meter's calibration unsuitable. You'll need to get it re-aligned from some calibration house. Or if any of your friends has a calibrator, you could calibrate it yourself. But this meter cannot be aligned without proper equipment. This is the biggest downside of this meter.But you may still be able to use your meter confidently without new calibration by keeping minor variation of say a few 10s of digits in mind while using it.Regarding the resistive voltage divider, as bdunham7 pointed out. Pin1 and 2 are 10 MegaOhm resistor and there is no connection of it with others. The other 4 resistors have one common pin.I hope it'll help.Edit: I forgot to mention one little detail regarding MOV testing. My insulation resistance meter outputs 524V at 500V setting. The next lower range is 450V and it outputs 477V. A good 560V MOV shows 120 MegaOhm and climbing at 524V and 2.0 GigaOhms and climbing at 477V. Please take that into account when you are testing MOV for a multimeter.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 20, 2025, 08:38:49 am
content: Quote from: mqsaharan on April 19, 2025, 05:49:16 pmAll I could think of is that maybe the meter is rounding down to zero when it sees a very low drop on a Schottky junctionQuote from: mqsaharan on April 19, 2025, 05:49:16 pmThat's a good spot, if they are the same. It would make some sense to have some commonality of front end parts.Quote from: mqsaharan on April 19, 2025, 05:49:16 pmNot a bad idea, to see if the fault is shared. That would imply either a failing analogue switch in the front end asic, or once again we come back to board contamination of some sort.Quote from: mqsaharan on April 19, 2025, 05:49:16 pmThe circuit path for this is going to vary considerably, depending on the rotary switch position.If not already done, it's worth checking the rotary switch contacts for damage/contamination too. Be careful, the spring contacts are mechanically fragile, and easy to lose!

author: mqsaharan
author_rank: Regular Contributor
timestamp: April 20, 2025, 11:28:48 am
content: Quote from: AVGresponding on April 20, 2025, 08:38:49 amI am somewhat certain they are the same ICs. But I don't have any way to check or prove it. Looking at the schematics of 189II and 87V, they are using different network dividers indeed but the rest of the support circuitry which consists of a few components is the same.Quote from: AVGresponding on April 20, 2025, 08:38:49 amSince OP has cleaned the board with IPA, I guess the contamination may not be the issue here.Quote from: AVGresponding on April 20, 2025, 08:38:49 amSince the meter is Off and OP is measuring right at the resistive divider and not at the input terminals, I guess the switch position will not matter.In order to check the rotary switch, OP has to disassemble it. The spring contacts are embedded into the housing in this meter but they are delicate indeed.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 21, 2025, 09:02:44 am
content: Quote from: mqsaharan on April 20, 2025, 11:28:48 amCleaning can take multiple passes sometimes. I'm not saying I definitely think itis, I'm just saying I wouldn't rule it outcompletely, just yet.Quote from: mqsaharan on April 20, 2025, 11:28:48 amThe rotary switch isn't the power control on these; they have a soft-power button instead. It can be in any position with the meter off.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 21, 2025, 11:49:28 am
content: Let me confirm. Does the meter only reads high in 500K range and above? At lower range it's OK right? I think there is a problem with the 1 MicroAmp constant current from the meter.

author: mqsaharan
author_rank: Regular Contributor
timestamp: April 21, 2025, 12:35:56 pm
content: Quote from: AVGresponding on April 21, 2025, 09:02:44 amYou are right. We cannot definitively rule out contamination. But the problem is meter is not physically with us. And we have to think and suggest according to the OPs replies.Quote from: AVGresponding on April 21, 2025, 09:02:44 amThe reason I am stating that the meter being Off needs to be considered is because the resistor network is attached directly to the front end chip and the analog switches within it are operated via some signal after applying power to the chip.I am actually only assuming here that they are disconnected. I only checked it with a few non-Fluke multimeters and they were disconnected in them.Quote from: BeBuLamar on April 21, 2025, 11:49:28 amWell, you are right. But the problem is the current source is built right into the front end chip with just a few helper components attached to it on the outside. So there is no way to repair it without replacing the whole chip. It is getting its signal from MSP430 but I am assuming that perhaps that microcontroller is OK.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 21, 2025, 03:21:17 pm
content: yes, it showed significant error when measuring the resistance higher 50kΩ

author: mqsaharan
author_rank: Regular Contributor
timestamp: April 21, 2025, 05:28:01 pm
content: Quote from: Els_Chaos on April 21, 2025, 03:21:17 pmI hope you have tried it after removing those protection components. Also, have you made sure your meter is contamination free.If you are positive that your front end chip is faulty, in my opinion, you have two options.1. Since you wrote that only Resistance function is faulty, so ignore it and keep using your meter as it is and use the Resistance function from your other meter.2. Replace the front end chip.I'll say it again, you need to make sure that the front end chip is faulty. Otherwise, the repair will not only cost you money but it may also make your meter unusable without alignment. And as I understand it, the alignment of such an instrument will cost a pretty penny. And depending on the facilities available at your location, you may not even get proper alignment.If you want to replace that front end chip, the author of this video might be of some help. He is from Philippines. If you asked him, he may give you some clue where you can source such an IC.""I am sorry, I don't have any more suggestions to diagnose/repair your meter. I hope other members have some more/better suggestions that will be helpful for you.Edit: Making some failed attempts to show the link instead of the video.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 22, 2025, 02:32:41 am
content: i just borrow my teacher FLuke 45 and made some new tests with components. It seems like that the 1uA current sources has some trouble with it. The capacitance measuring is fine, however, the diode mode also facing with some problems.

author: bdunham7
author_rank: Super Contributor
timestamp: April 22, 2025, 03:22:37 am
content: Looks like your Vfreadings are all low on the diode mode? You don't know the history on this meter so it is possible that it was calibrated with an existing problem. In any case and in the absence of a clear direction or a better idea, I would recommend that you try desoldering and setting aside CR4, CR3, R29 and R172. If you want to take one off at a time and retest each time then do it in that order--otherwise just take them all off and keep track of which is which.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 22, 2025, 11:22:56 am
content: Quote from: Els_Chaos on April 22, 2025, 02:32:41 amI suspect that the 1 microamp is higher than 1 microamp however the Fluke 45 doesn't have resolution nor accuracy to measure the 1 microamp accurately.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 22, 2025, 02:53:36 pm
content: So i need a better VOM right. I just saw him had a 6+1/2 digits table multimeter, maybe i will try to ask him for using it.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 22, 2025, 05:12:10 pm
content: Depends on the meter; my 6.5d Keithleys/Agilent have 10nA resolution, for example, but my 5.5d Keithley has 0.1nA resolution...For your needs, 10nA resolutionshouldbe fine.

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 28, 2025, 05:33:27 am
content: well, i just ordered a replacement for fluke customed and components for input protection. Should i replace the old one?

author: Els_Chaos
author_rank: Regular Contributor
timestamp: April 28, 2025, 07:17:01 am
content: Do i need to bring it to calibrating service after replacing the old component?

author: AVGresponding
author_rank: Super Contributor
timestamp: April 28, 2025, 07:51:07 am
content: Most certainly; the meter calibration will be adjusted to match the characteristics of the old IC, and the new one will be different enough to cause noticable errors in every range, probably.