Repair of Aneng AN8009 meter - erroneous ohmmeter readings

Olkus 31 Aug 2024 12:49 34 4674 Cool? (+9)

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TL;DR

The Aneng AN8009 multimeter showed wildly wrong ohmmeter readings, misreading a 100 ohm resistor as tens of kiloohms and even displaying nonsense with open or shorted probes.
Cleaning the range switch and its PCB tracks fixed the fault; oily grease had leaked from the switch onto the board, and the contacts were washed as well.
The meter’s original 100uF supply electrolytic was upgraded to 1000uF, one of the recommended AN8009 modifications.
After reassembly, the ohmmeter readings returned to correct values and the repair was completed in about half an hour at a cost of 0zł.
The rotary switch is a common failure point in many meters because it also handles power switching, which accelerates wear.

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Welcome,

Today I will give a description of a simple repair of this multimeter. The equipment is popular enough that maybe someone less familiar with the subject will find this description useful and save his instrument

The meter on the ohmmeter range indicated all sorts of silly things, e.g. a 100 ohm resistor was identified as being up to several tens of kiloohms. Without the probes plugged in, it was also able to display some nonsense, and when the probes were short-circuited, instead of zero the display could show several hundred ohms or even more.
The first suspects were the batteries. I bought the meter in the first half of 2021 and it has been running on the same set of batteries ever since, and I use it the most out of all the meters I own. However, the cells turned out to be in pretty good shape, I even swapped them for new ones just to be sure, but it didn't do anything.
What I observed later, normal readings could be restored (but not always) by switching between ranges a few times. So the main suspect became the switch. To get to it the meter has to be disassembled, after dismantling the casing and removing the board we have this view:

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You can see the switch tracks, they appear to be gold plated.
If you look closely you can see the oily ooze on the board:

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This is probably grease that leaked from the switch and got on the PCB.
The part with the knob on the underside:

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Here the contacts look OK, however I also washed them just in case.
The switch tracks after cleaning:

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You can see a huge difference, clean was not there:

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Taking advantage of the fact that I had the meter open I also replaced the original 100uF electrolyte on the meter supply with a 1000uF:

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This is one of the recommended modifications for this meter, you can read more here: https://www.elektroda.pl/rtvforum/topic3713925.html#18825243
Well, and now the most important thing: Was the repair successful, does the meter indicate as it should? Time to check!

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It worked and the readings returned to correct

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The whole repair took me ~ half an hour, cost 0zł

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The switch, by the way, is a common problem with many meters, mainly because the power switch is usually placed there as well, so the switch wears out faster because of this.
Thank you for your attention.

Regards,
A.

About Author

Olkus wrote 3910 posts with rating 910 , helped 132 times. Live in city kraków. Been with us since 2020 year.

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NegativeFeedback 31 Aug 2024 16:07

This grease is probably silicone grease, which is used to lubricate the contact area so that the contacts do not degrade quickly, due to the poor quality of the pcb and copper plating, so I would suggest... [Read more]

Olkus 31 Aug 2024 16:12

. Well in this case it was making it worse. The ohmmeter was going crazy before and now it works normally, so I guess there was something not quite right with the grease? Greetings, A. [Read more]

waldi_8601 31 Aug 2024 22:32

I don't think the grease itself is the problem, I've usually seen clear grease used for such purposes, its purpose is rather to reduce friction, mechanical wear of the contacts/PCB. Here on the PCB you... [Read more]

Olkus 01 Sep 2024 00:43

. Basically such a grease, in this case probably silicone, is an insulator. If it gets between the contacts of the switch and the copper fields on the PCB then things like this can happen. Well, and... [Read more]

Krzysztof Kamienski 01 Sep 2024 04:00

. With good contact pressure, this grease is not an insulator, and actually contributes to prolonging the life of the switch. Unless I am mistaken and the instrument was designed by a Chinese idiot. [Read more]

E8600 01 Sep 2024 09:51

The grease should be the problem is the switch in the dial instead of a separate separate button. [Read more]

Olkus 01 Sep 2024 10:15

To dispel doubts I looked at another meter - UNI-T UT33D+, the grease is: https://obrazki.elektroda.pl/7145117300_1725178412_thumb.jpg https://obrazki.elektroda.pl/7967320000_1725178412_thumb.jpg... [Read more]

forest1600 01 Sep 2024 10:45

You can always use it without grease for a test and see what condition the tracks are in after a year. [Read more]

PPK 01 Sep 2024 15:04

In my case the problem was the banana sockets. I have solid, proprietary wires, 1.5mm2 in silicone, 'gold-plated' plugs. On a DT-9935 bridge, they had a resistance of 0.1 R. Meanwhile, Aneng, (shorted),... [Read more]

kris8888 01 Sep 2024 17:00

I also recently cleaned my old multimeter, it works perfectly, but I have a dilemma whether to give silicone grease to those switch contacts or better to give non-acid technical petroleum jelly? Or maybe... [Read more]

slavo666 01 Sep 2024 22:13

This will neither help nor harm you. A crappy switch won't fix it, and a decent one won't hurt you either. [Read more]

PPK 02 Sep 2024 00:34

For multimeters I have not used it but for switches it is ideal. I have rescued old isostats and decade/BCD switches with it, among others. Only for flat switches you would have to give a thin layer so... [Read more]

kris8888 02 Sep 2024 00:38

This is probably unsuitable since from the description it appears to conduct electricity. It will make "shorts" or leakage between the tracks on the switch board. [Read more]

PPK 02 Sep 2024 00:45

. Well I had that in the 10/BCD rotary switches, because there is just such a circular plate etched into the laminate and microsteps. When I gave too much, it actually made short circuits. But when I... [Read more]

Olkus 02 Sep 2024 07:41

. The wires as well as the sockets in this case are OK. Although I have some Chinese meter where the wires themselves have 5 ohms :) . . Maybe that would be a good solution. Or Contact 61. ... [Read more]

fiB 02 Sep 2024 11:21

the link to the modification topic provided also contained a solution to your problem at the end. I had a similar problem a year ago. A year after cleaning and applying new grease, the multimeter works... [Read more]

Olkus 02 Sep 2024 15:24

. I also have this suspicion that there is something wrong with the factory one. I will probably buy the correct one unless Fellows can advise something else. Regards, A. [Read more]

sq3evp 02 Sep 2024 15:49

And brag about what you cleaned so beautifully with? Chemistry or just a decent stick? [Read more]

Olkus 02 Sep 2024 16:13

. IPA :) . Regards, A. [Read more]

FAQ

TL;DR: If your Aneng AN8009 shows 100 Ω as tens of kΩ, clean the rotary switch PCB first. One user fixed it in ~30 minutes for 0 zł after saying the ohmmeter was "going crazy." This FAQ helps AN8009 owners restore correct resistance readings and check whether the real fault is the switch, sockets, or leads. [#21210334]

Why it matters: Low-ohm faults in the range switch can corrupt basic continuity and resistance checks, making an otherwise usable multimeter unreliable.

Option	What users observed	Cost / effort	Best use
Clean switch tracks with IPA	Restored correct ohmmeter readings after grease and dirt removal	0 zł, ~30 min	First repair step
Re-grease after cleaning	Some users report 1 year of stable readings with fresh grease	Extra materials, repeat teardown	If the original grease was contaminated
Leave switch dry	Chosen by the repair author after cleaning	0 zł	When gold-plated tracks already work correctly
Replace banana sockets / improve leads	Reduced shorted-probe reading from 10–20 Ω to 0.3–0.4 Ω in one case	~25 PLN + 1 hour	If switch cleaning does not fix low-ohm error

Key insight: The thread points to contaminated switch grease and dirty range-switch tracks as the main cause of wildly wrong ohmmeter readings. If cleaning does not restore near-zero readings with shorted probes, check the input sockets and test leads next.

Quick Facts

The original repair fixed the meter after cleaning the rotary switch PCB, took about half an hour, and cost 0 zł. [#21210334]
The failure symptom was severe: a 100 Ω resistor could read as several tens of kΩ, and shorted probes could show several hundred ohms. [#21210334]
The author had used the meter since the first half of 2021 on the same batteries, but battery replacement did not solve the problem. [#21210334]
One user improved low-resistance performance by replacing poor banana sockets, cutting shorted-probe readings from 10–20 Ω to 0.3–0.4 Ω; the mod cost about 25 PLN and 1 hour. [#21211496]
A common optional AN8009 modification mentioned in the thread is increasing the power-supply capacitor from 100 µF to 1000 µF while the meter is already open. [#21210334]

How do I fix an Aneng AN8009 that shows wildly wrong resistance values on the ohmmeter range?

Start by cleaning the rotary range switch PCB and its contact area. In the reported repair, batteries were ruled out first, then the meter was opened, oily dirt was removed from the switch tracks, and correct readings returned immediately. The whole job took about 30 minutes and cost 0 zł. If the meter still shows high resistance with shorted probes after cleaning, check the banana sockets and test leads next. [#21210334]

What symptoms point to a dirty or failing rotary range switch in a digital multimeter like the Aneng AN8009?

The clearest symptom is unstable resistance readings that change with switch movement. In the thread, a 100 Ω resistor read as several tens of kΩ, open probes showed nonsense values, and shorted probes could show several hundred ohms instead of near zero. Another strong clue is that switching ranges several times can briefly restore normal operation. [#21210334]

Why can switching ranges several times temporarily restore normal ohmmeter readings in an Aneng AN8009?

Repeatedly turning the selector can momentarily improve contact between the wiper and dirty PCB tracks. The author observed that normal readings sometimes returned after moving through several ranges, which strongly implicates the rotary switch rather than the batteries. That temporary recovery usually means contamination or wear is present, not that the fault is gone. [#21210334]

What is the proper step-by-step way to disassemble, clean, and reassemble the AN8009 range switch PCB?

Use a simple 3-step process. 1. Remove the case, take out the PCB, and expose the rotary switch tracks. 2. Clean the visible grease and dirt from the PCB tracks and the underside contact part; the author used IPA. 3. Reassemble the meter and verify with a known resistor and shorted probes. In the thread, this restored correct readings without replacing parts. [#21212730]

Which cleaner works best for removing leaked grease and dirt from multimeter switch tracks: IPA, Contact 61, or potentiometer spray?

IPA is the only cleaner in the thread that clearly solved the fault. The author answered directly that the switch was cleaned with IPA, and after that the AN8009 returned to correct ohmmeter readings. Contact 61 and potentiometer spray were only proposed later as possible options, not confirmed fixes in this repair. [#21212730]

Silicone grease vs non-acid technical petroleum jelly: which is better for rotary switch contacts in a multimeter?

The thread does not show a clear winner, but it leans toward silicone grease over petroleum jelly for relubrication. Several users discussed silicone grease as the intended type, and one user reported a year of stable operation after cleaning and applying fresh SGB grease. Petroleum jelly was raised as an option, but no successful multimeter result was documented for it in the thread. [#21212353]

How much does the contact material matter when choosing a lubricant for multimeter switch contacts?

It matters a lot, because users in the thread treated gold-plated and silver contacts as different cases. Gold-plated rotary tracks were debated because grease can either protect a thin surface or raise contact resistance in low-current measurement circuits. By contrast, silver Isostat contacts were mentioned as a separate case with different aging behavior. [#21222833]

What is SGB grease, and why do some users recommend it for rotary switch contacts after cleaning?

"SGB grease" is a contact lubricant that users apply to rotary switch interfaces after cleaning, with the key characteristic that it is used in a very thin replacement layer after old grease and dirt are removed. One user recommended it because an AN8009 with similar symptoms worked correctly for a full year after cleaning and regreasing with SGB. [#21212353]

What is an Isostat switch, and how is it different from the gold-plated rotary range switch used in meters like the AN8009?

"Isostat" is a pushbutton switch family that routes signals through silver contacts, a key characteristic that differs from the gold-plated circular PCB tracks used in a multimeter’s rotary range selector. In the thread, users stressed that old Isostat experience does not transfer directly, because silver and gold contacts age and react differently. [#21222833]

Why do some users say grease protects gold-plated switch tracks, while others say it increases contact resistance and ruins low-ohm readings?

Both views came from different failure modes seen in practice. Some users said grease reduces friction and wear on thin gold plating, especially in selectors that also act as power switches. Others reported that contaminated or misplaced grease raises contact resistance, and one commenter argued this is especially harmful in modern meters that measure resistance with very low current. [#21214752]

When should I leave a multimeter range switch dry instead of relubricating it after cleaning?

Leave it dry when cleaning alone restores stable readings and the gold-plated tracks look healthy. That is exactly what the repair author decided after the discussion, choosing to run the AN8009 without new grease and monitor long-term wear. This is the safest choice when the original grease appears dirty, migrated, or electrically troublesome. [#21215616]

How can dirty grease, metal filings, or corrosion on switch tracks create leakage paths and cause false resistance measurements?

Dirty grease can spread across adjacent switch fields and stop the contact from making a clean, low-resistance connection. One user specifically pointed to grease contaminated with micro filings or corrosion, saying it can begin to conduct to some extent and bridge contact areas. In an ohmmeter circuit, that leakage distorts low-value readings and can make shorted probes read far above zero. [#21210879]

What other faults besides the range switch can make an Aneng meter read 10–20 ohms with the probes shorted, such as bad banana sockets or poor test leads?

Bad banana sockets and poor leads can cause the same symptom. One user reported an Aneng that showed 10–20 Ω with the probes shorted, then traced the fault to cheap internal sockets made from tinned sheet material. The thread also warns that some cheap test leads can add several ohms on their own, so verify leads and jacks before blaming the ADC or firmware. [#21211496]

How do upgraded banana sockets and better test leads improve low-resistance readings in Aneng multimeters?

They reduce series resistance between the meter input and the probe tip. In the thread, replacing the original sockets with gold-plated bronze types changed the shorted-probe reading from 10–20 Ω down to about 0.3–0.4 Ω, and the modified meter also passed a 10 A load test. Better leads help for the same reason: less contact loss and less conductor resistance. [#21211496]

Why do users replace the Aneng AN8009 power-supply capacitor from 100 uF to 1000 uF, and what effect does that modification have?

Users do it as a recommended AN8009 modification while the meter is already open. The repair author replaced the original 100 µF electrolytic with a 1000 µF part during the same teardown, citing an existing modification thread. This change was not presented as the cause of the ohmmeter fix, but as a separate preventive or performance-oriented upgrade. [#21210334]

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