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Repair of Aneng AN8009 meter - erroneous ohmmeter readings

Olkus 3627 34
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  • ANENG AN8009 multimeter in ohmmeter mode with display showing OL, with red and black test leads next to it. .

    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:
    Inside view of a disassembled multimeter showing PCB and switch tracks. .
    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:
    Close-up of a multimeter circuit board showing switch traces. Image of gold-plated tracks in a multimeter switch after cleaning. .
    This is probably grease that leaked from the switch and got on the PCB.
    The part with the knob on the underside:
    Close-up of the multimeter switch interior after cleaning. .
    Here the contacts look OK, however I also washed them just in case.
    The switch tracks after cleaning:
    Close-up of a PCB with visible gold-plated traces. .
    You can see a huge difference, clean was not there:
    A cotton swab with dirt on the tip against a workbench background. .
    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:
    Electrolytic capacitor 10V 100μF lying on a grid mat. View of an open multimeter showing the interior with PCB and replaced capacitor. .
    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!
    ANENG AN8009 multimeter with display showing 0.004 ohms, with probes in hand. .
    It worked and the readings returned to correct :D .
    The whole repair took me ~ half an hour, cost 0zł ;) .
    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.

    Cool? Ranking DIY
    About Author
    Olkus
    Level 32  
    Offline 
    Olkus wrote 3731 posts with rating 830, helped 131 times. Live in city kraków. Been with us since 2020 year.
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  • #2 21210553
    NegativeFeedback
    Level 14  
    Olkus wrote:
    [url=https://
    This is probably grease that leaked from the switch and got on the PCB.
    A.


    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 disassembling again and lubricating there.
    The grease does not degrade the contact, I sometimes grease old instruments that have deteriorated after many years of use, I have been using these for many years, I have never had a problem with the contacts because of this.
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  • #3 21210559
    Olkus
    Level 32  
    NegativeFeedback wrote:
    Grease does not deteriorate the contact, I sometimes grease old instruments in this way that have deteriorated after many years of use, I have been using these for many years, I have never had a problem with the contacts because of this.
    .

    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.
  • #4 21210879
    waldi_8601
    Level 13  
    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 can clearly see the grease is dirty, maybe some micro filings, corrosion, so it could start to conduct current to some extent, spread it connects the contact fields and the meter in such a situation could start to malfunction.
  • #5 21210963
    Olkus
    Level 32  
    waldi_8601 wrote:
    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 can clearly see the grease is dirty, maybe some micro filings, corrosion, so it could start to conduct current to some extent, smeared connects the contact fields and the meter in such a situation could start to malfunction.
    .

    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 the aforementioned dirt certainly made things worse too.

    Regards,
    A.
  • #6 21210978
    Krzysztof Kamienski
    Level 43  
    Olkus wrote:
    this is an insulator. If it gets between the contacts of the switch and the copper fields on the PCB then just such things can happen
    .
    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.
  • #7 21211068
    E8600
    Level 41  
    The grease should be the problem is the switch in the dial instead of a separate separate button.
  • #8 21211091
    Olkus
    Level 32  
    To dispel doubts I looked at another meter - UNI-T UT33D+, the grease is:
    Disassembled UNI-T UT33D+ multimeter showing the circuit board. Image of a multimeter interior showing a dusty printed circuit board. .
    So it looks like dirt was the culprit, or this grease was somehow left and started to conduct after some time.
    I'll have to buy silicone grease in that case, as I don't currently have any and give it a bit to this Anenga.

    E8600 wrote:
    The grease should be the problem is the switch in the dial instead of a separate separate button.


    Yes, that certainly has an impact too, as I wrote about at the end of the article.

    Regards,
    A.
  • #9 21211123
    forest1600
    Level 20  
    You can always use it without grease for a test and see what condition the tracks are in after a year.
  • #10 21211496
    PPK
    Level 29  
    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), was showing a resistance of 10-20 R. The problem turned out to be the banana sockets made internally of tinned 'tinned' sheet metal, I think. After replacing them with 'gold-plated bronze' sockets (acoustic - a minor modification). The ohmmeter showed 0.3-0.4R. The 10 A load test also passed without a problem. Cost, approx. 25 PLN + 1 hour of work.
  • #11 21211619
    kris8888
    Level 39  
    Olkus wrote:
    I'll have to buy silicone grease in that case, because I don't currently have it, and give some to that Anenga.

    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 it is better not to lubricate anything there. Maybe someone has experience and will write all the pros and cons. Does the material the contacts are made of also make a difference in terms of the choice of "lubricant"?
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  • #12 21212014
    slavo666
    Level 23  
    This will neither help nor harm you. A crappy switch won't fix it, and a decent one won't hurt you either.
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  • #14 21212107
    kris8888
    Level 39  
    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.
  • #15 21212112
    PPK
    Level 29  
    kris8888 wrote:
    This is probably not suitable since from the description it appears to conduct electricity. It will make "shorts" or leakage between the tracks on the switch board.
    .
    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 rubbed it in with a cloth, the switch started to work properly and it's been working for 4 years now.... Another method is this spray for potentiometers - AG - Only you also have to wipe off the excess and dry.
  • #16 21212163
    Olkus
    Level 32  
    PPK wrote:
    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), was showing a resistance of 10-20 R. The problem turned out to be the banana sockets made internally of tinned 'tinned' sheet metal, I think. After replacing them with 'gold-plated bronze' sockets (acoustic - a minor modification). The ohmmeter showed 0.3-0.4R. The 10 A load test also passed without a problem. Cost, about 25 PLN + 1 hour of work.
    .

    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 :) .

    PPK wrote:
    Another method is this spray for potentiometers - AG - Only you also have to wipe off the excess and dry.
    .

    Maybe that would be a good solution. Or Contact 61.

    Regards,
    A.
  • #17 21212353
    fiB
    Level 13  
    >>21210334 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 fine and the ohmmeter readings are repeatable. I used SGB grease, I suspect that the one applied from the factory is of low quality and creates problems after a while.
  • #18 21212674
    Olkus
    Level 32  
    fiB wrote:
    I suspect that the one applied at the factory is of low quality and creates problems after some time.
    .

    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.
  • #19 21212707
    sq3evp
    Level 37  
    Olkus wrote:
    .
    Here the contacts look OK, however I also washed them just in case.
    Switch tracks after cleaning:

    And brag about what you cleaned so beautifully with?
    Chemistry or just a decent stick?
  • #20 21212730
    Olkus
    Level 32  
    sq3evp wrote:
    Are you bragging about what you cleaned so beautifully with?
    Chemistry or just a decent stick?
    .

    IPA :) .

    Regards,
    A.
  • #21 21214752
    398216 Usunięty
    Level 43  
    NegativeFeedback wrote:
    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 there to disassemble again and lubricate.
    .
    Protect the gold-plated tracks? Unfortunately, but the Author's colleague got it right - that grease (whatever it may be; be it silicone or tow) does more harm than good. The resistance it introduces into the circuit (and modern, better class meters measure resistances with an extremely low current) falsifies the readings - not only the ohmmeter's, by the way. I myself had a similar symptom in another meter - the grease on the contacts turned out to have migrated from the "terkotki" that allows the range switch to be stabilised in the correct (for the contacts) position.
  • #22 21214775
    kris8888
    Level 39  
    398216 Usunięty wrote:
    Protect the gold-plated tracks? Unfortunately, but the Author's colleague got it right - that grease (whatever it may be; be it silicone or towote) does more harm than good
    .
    Well that's right, it's good that you confirm. I also had an assumption that gold-plated contacts and tracks should rather not be lubricated with anything. And if they are, you should think carefully about what.
    I checked at my place in some older oscilloscope where there are also gold plated contacts of multi-turn switches, there is no grease on them and you can't see that it was ever there.

    On the other hand, I recently disassembled a rotary motorised input switch in a top-of-the-range Sony amplifier and there the contacts were clearly factory lubricated with something. The contacts looked gold-plated and the grease was unlikely to have come from the mechanism itself.
  • #23 21214825
    E8600
    Level 41  
    I had a similar thought myself and once wiped it down, and while the contacts survived, the metal plates in the dial had become so bad that some had cracked. I then folded on what I had which was a thin layer of Vaseline with a drop of Vaseline oil.
  • #24 21214855
    Nori2
    Level 22  
    kris8888 wrote:
    in some older oscilloscope where the contacts of the multi-turn switches are also gold plated, there is no grease on them and you can't see there ever was
    .
    kris8888 wrote:
    in a top of the range Sony amplifier and there the contacts were clearly factory lubricated with something. The contacts appeared to be gold plated and the grease was unlikely to have come from the mechanism itself
    .
    What conclusion can be drawn from this?

    The contacts used to be "richly" gold-plated, but now, in an age of cost-cutting, they are only "flicked" with gold.
    The lubricant is supposed to protect the gold-plated contacts from mechanical wear too quickly.
  • #25 21215530
    398216 Usunięty
    Level 43  
    E8600 wrote:
    I once wiped it down and while the contacts survived, the plates in the dial became so bad that some cracked.
    .
    This is not a good indication of the lamellas rather than a lack of lubricant. Well-made switch plates (especially not airtight ones!!!) HAVE NO RIGHT to crack or wear out. Because (according to common sense) from what? The smooth gold-plated contacts on the laminate? Or from dust and dirt that ALWAYS gets into such (non-hermetic switches)? Meters are supposed to measure correctly and that is the most important thing. And if someone is not able to make smooth contacts, properly gild them or select metal for the switch's moving contacts, is this a reason to try to get around the problem by lubricating the contacts? Grease < and as we know, grease is extremely fond of binding dust, dirt and other nasties to itself, and I don't think anyone needs to be told how such abrasive paste behaves on the contacts....
    GREASE WAS USED IN SWITCHES WITH A SLIGHTLY DIFFERENT DESIGN AND, ABOVE ALL, DIFFERENT SWITCHING SIGNALS. And even so, such switches were capable of tripping, breaking, cracking... in audio equipment, for example.
  • #26 21215616
    Olkus
    Level 32  
    kris8888 wrote:
    398216 Usunięty wrote:
    Protect the gold-plated tracks? Unfortunately, but the Author's colleague got it right - that grease (whatever it may be; be it silicone or towote) does more harm than good
    .
    Well that's right, it's good that you confirm. I also had a conjecture that gold-plated contacts and tracks should rather not be lubricated with anything. And if they are, you have to think carefully about what.


    In that case I leave the switch without lubrication, as I thought at the beginning. We'll see if this causes any problems after a while, although I don't think it will happen quickly.

    Regards,
    A.
  • #27 21222126
    keseszel
    Level 26  
    Often a sore point is mangy wires. I generally make my own,try to give good, expensive banks, the wire I used to give in insulation, 1.5mm sq or 1mm, secured with Distal and hot glue or butaprene. Meter wires are the last fall they add, miracle not headphone wires. But still I often get strange measurements. Gold plated contacts don't get protected, the grease is actually supposed to improve the feed rate because the fields are rubbing out, I have some older bullseye meters.
  • #28 21222170
    Olkus
    Level 32  
    keseszel wrote:
    Frequently the problem is scabby wires. I generally make my own,try to give good, expensive banks, wire I used to give in insulation, 1.5mm sq or 1mm, secured with Distal and hot glue or butaprene. Meter wires are the last fall they add, miracle not headphone wires. But still, I often get strange measurements.


    In this case it wasn't the wires that were the problem, I checked that at the outset.

    keseszel wrote:
    Golden contacts don't get protected, the grease is actually supposed to improve the feed rate, because the fields are rubbing out, I have some older bull gauges.


    So if the contacts are gold plated we don't give grease as some have written before?

    Greetings,
    A.
  • #29 21222339
    keseszel
    Level 26  
    Olkus wrote:
    So if the contacts are gold plated we don't give grease, as some have written before?
    .
    That's how I remembered it from the old days. But I remember the Isostats strewn about. I would give but would get an idea of what lubricants would be advisable these days. No matter what you do it will still be fine. You don't buy a meter for life ;-) .
  • #30 21222483
    Olkus
    Level 32  
    keseszel wrote:
    This is how I remembered from the old days. But I do remember the Isostats strewn about. I would give but would get an idea of what lubricants would be advisable these days. No matter what you do it will still be fine. You don't buy a meter for life .
    .

    Now it's probably silicone grease that would be most advisable. I leave it without for now, you are right , that you do not buy a meter for life :) Especially since the one from the topic is not very expensive, and in case of emergency I have other ;) .

    Regards,
    A.
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Topic summary

The discussion revolves around the repair of the Aneng AN8009 multimeter, specifically addressing erroneous ohmmeter readings. The user initially suspected battery issues but found them to be in good condition. Subsequent troubleshooting pointed to potential problems with grease on the contacts, which may have caused erratic readings. Various participants shared insights on the use of silicone grease versus petroleum jelly, with some suggesting that grease can introduce resistance and lead to inaccurate measurements. Others noted that dirt and corrosion could exacerbate contact issues. A participant resolved their problem by replacing the banana sockets with higher quality components, resulting in improved resistance readings. The conversation concluded with considerations on whether to lubricate contacts, particularly gold-plated ones, and the implications of using different types of lubricants.
Summary generated by the language model.
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