Multimeter Amprobe, selector problem - Page 1
Forum section: electronics / beginners

author: DisasterNow
author_rank: Regular Contributor
timestamp: January 31, 2023, 06:42:25 pm
content: Hello, I have an Amprobe AM 510 multimeter, and I have a problem with the measurement selector: when I select the current measurement in uA scale, sometimes I see the current measurement, other times the resistance measurement. Maybe I need to clean the internal contacts of the selector? Thank you

author: DisasterNow
author_rank: Regular Contributor
timestamp: January 31, 2023, 07:13:45 pm
content: I removed the card, I see that there is a slight layer on the selector contacts (it can be removed with a finger). Maybe factory fat?

author: Gyro
author_rank: Super Contributor
timestamp: January 31, 2023, 08:30:42 pm
content: 'Factory fat" is a new term for me, but it is factory (deliberately) applied contact lubricant.

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 09:24:51 pm
content: Mmmmm .. factoy fat! Droollll...

author: EPAIII
author_rank: Super Contributor
timestamp: February 01, 2023, 02:31:11 am
content: Yes, that is a lubricant. When one part moves in contact with another they can wear. The lubricant was applied to minimize that and maximize the life of the switch. I would not remove it.Perhaps one of the fingers on the rotor of the switch is a bit bent and not making firm contact. You could gently, I SAY GENTLY, press on each of them in turn to see if that makes the display read correctly.If this is a new meter, I would try to return it for a refund or replacement. Or contact Amprobe.

author: DisasterNow
author_rank: Regular Contributor
timestamp: February 01, 2023, 05:26:13 am
content: I've had this multimeter for 10 years; I will try to check the contacts on the rotor. Ok I'll leave the lube. On electrical rubbing contacts, what type of lubricant is typically used? Thanks

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 20, 2025, 01:00:14 am
content: I'm reopening this discussion because now, sometimes, when I set the selector switch to resistance (and then select the continuity function with the button), if I touch a probe with my finger, I hear some noise from inside the multimeter, but it still detects continuity everywhere. I've noticed that by pressing the selector switch down a little more, it starts working properly. So it's still a selector problem, as I described two and a half years ago. At this point, I'd be ready to scrap it, but maybe first I could try cleaning the selector contacts and tracks with isopropyl alcohol? Okay, I'd remove the rotation lubricant, but I'd probably scrap it anyway (we can afford any attempt, even destructive ones...). Any advice?

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: August 20, 2025, 01:29:32 am
content: Dielectric Grease will replace it, clean good and increase contact tension.Jeff

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 20, 2025, 12:46:14 pm
content: [I removed my previous message, and inserted this new one after reading old discussions on the topic]Thanks Jeff.In the meantime, I've been reading some discussions on this forum about the question of the century: grease on the selector contacts? Yes or no?I haven't gotten a convincing answer.I'll stick to the facts: my Amprobe left the factory with grease on the rotary selector contacts (shown in the second photo).It worked fine for years, but now and a few years ago it's having some problems, as if it doesn't know which setting it's set to. I think this is due to that old grease, certainly not to wear on the contacts (which I don't see).I've decided to thoroughly clean the selector contacts with isopropyl alcohol, and I'll leave them dry. I'll try using it that way and see if it's better or worse.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 21, 2025, 12:17:55 pm
content: I cleaned the grease from the rotary selector contacts with ISP. When I reassembled the board, however, I noticed that the screw holding the board to the selector (it's marked in red in the image, it also has a small plastic washer) never reaches its end. It's as if the female thread in the selector is damaged. I don't know if this is normal, or if this could also be the cause of the interference between the various functions, as it doesn't hold the board to the rotary selector. Now I'll try using it this way with dry contacts. If the problem recurs, I'll try retightening that screw...

author: mqsaharan
author_rank: Regular Contributor
timestamp: August 22, 2025, 07:19:29 am
content: Hi DisasterNow,It is always better to put some lube on PCB tracks for rotary switch. Because there is metal on metal rubbing action going on there. The copper tracks on the circuit board are plated and the plating is very thin. When the wiper contacts slide on these tracks dry, the plating rubs off more easily. Once the copper is exposed, it gets oxidized and cause contact problems. The wiper contacts are made of very thin sheet metal. Even though they don't put too much pressure, it is still enough when they slide they rub off metal. So, to reduce the wear, always use some dielectric lube.If you would like to see what they look like when badly worn out, check out this video:https://youtu.be/x_L6Z8BAXFQ?t=1070If the screw holding the selector switch housing has slipped,you can use some small, thin pieces of foam or rubber on the circuit board all around the hole you have pointed to in your picture or behind the 9V battery holder inside the case to put pressure on the board so that it makes better contact with the selector switch housing containing the wiper contacts.This is not that good an idea. Please read the Edit below.The problem with your multimeter is obviously the switch contact problem. Clean the wiper contacts and the switch tracks on PCB with IPA, put some lube there, assemble it properly and I hope it'll work fine for years to come.I hope it helps.Edit: corrected spelling mistakes.Edit: It is better to use a little longer self tapping screw of same thickness to hold the housing at a proper distance or use a plastic shim ( a small circular plastic sheet) under the rotary housing containing the wiper contacts. There are plastic stand offs inside the top shell that'll not allow the PCB get pass a certain point when pushed down.

author: tooki
author_rank: Super Contributor
timestamp: August 22, 2025, 10:23:13 am
content: Quote from: DisasterNow on August 21, 2025, 12:17:55 pmWhy would you do that?!? That is just going to wear out the contacts much faster.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 22, 2025, 01:10:12 pm
content: Quote from: mqsaharan on August 22, 2025, 07:19:29 amI cleaned the tracks thoroughly. For now, however, I've left the contacts dry. I'm not sure what type of lubricant or grease to use. I've read several discussions here on the forum, but there are conflicting opinions. You're right about the screw, but I was wondering why they put a rubber washer on it. Perhaps because the screw needs to be tightened but not too much. ThanksQuote from: tooki on August 22, 2025, 10:23:13 amAs I mentioned above, I'm not sure what type of lubricant, or grease, to use. I've read that many multimeters have dry leads, while others have grease. The Amprobe in question had grease. However, I was having frequent problems with the mode selector, and I thought this old lubricant might be the cause. If I knew which product was recommended, I would definitely use it. Thanks, bye.

author: mqsaharan
author_rank: Regular Contributor
timestamp: August 22, 2025, 03:02:12 pm
content: Manufacturers use Silicone grease on these selector switch tracks. You can even use Silicone oil, if you have access to it. Just put a little grease on a lint free paper or cloth or soak a lint free paper or cloth in silicone oil and rub it on the tracks. Use as little as required.I am personally using petroleum based lithium grease meant for automotive for lubricating these tracks on one of my multimeters as an experiment and its been 6 years since I applied it. It is working fine and I have not seen any corrosion or any other problems due to this grease. Its in my use and I check it physically almost every year.My guess regarding your frequent troubles with selector switch is the slipped screw.I would suggest you to remove the wiper contact housing from the top shell. Just pry it from sides or pull it out. It is stuck there due to friction. Be mindful of the wiper contacts not to loose or damage them, as well as the orientation in which the housing go back in.Screw it to the PCB and then install the PCB in the top shell. Use a little longer self-tapping screw of the same thickness. If you can, drill a small hole first. It'll make it easy to put a longer screw in. Don't screw it all the way. Leave a little gap, say about 1mm between the PCB and the wiper housing. The screw is there only to keep it at a fixed distance and keep these wipers under reasonable pressure to make a good contact with the PCB tracks.The rubber washer you mentioned is there to prevent the screw head from grinding the PCB under it. You can put a piece of thin plastic there if you like.Lubricate the knob of this housing so that it doesn't get stuck in the main selector knob again.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 22, 2025, 04:01:04 pm
content: Quote from: mqsaharan on August 22, 2025, 03:02:12 pmThanks for the suggestions. I'm not at home right now, but I have various greases and oils. I'll take some photos and post them here in the discussion. Maybe I already have some products that might work.Okay, I'll disassemble the multimeter again and investigate the screw that screws into the selector switch from the board. I also think the greatest likelihood of an occasional failure is due to the tightness of that screw. Regarding the rubber/plastic washer, however, I have another hypothesis: that it serves precisely to prevent the screw from being fully tightened, and that rubber ensures it remains slightly loosened without being loosened further by vibrations. Could this be the case? I'll update the discussion later, thanks.

author: mqsaharan
author_rank: Regular Contributor
timestamp: August 22, 2025, 04:56:00 pm
content: I do not know much about greases and oils. Manufacturers use Silicone grease mainly because it does not dry with time. And it provides acceptable lubrication for the sliding switch contacts.So, please choose any grease that is non-conductive (which generally available greases are), thin/light not too thick and does not dry with time.Conductive greases are especially formulated for electrical contacts and is a bad choice here.As per my understanding, the screw stays there due to friction. It is not used to firmly attach the rotary housing to the PCB. Its job is to hold/keep it at a preset distance from the board.Please do not tight the screw too much.I am attaching here a few pictures of a different multiimeter, as an example, that uses same style for its rotary switch to make things clearer for you.I hope it helps.

author: tooki
author_rank: Super Contributor
timestamp: August 22, 2025, 06:31:32 pm
content: Quote from: DisasterNow on August 22, 2025, 01:10:12 pmI’m not sure why you’d think that the grease would cause the problems you have.Anyway, you want an electrical contact grease (often called dielectric grease). Definitely not some random lubricant. Many companies make electrical contact greases. Ideally, you’d want one optimized for gold-plated contacts and for maximum lubrication for moving contacts. Something like Deoxit FaderGrease or Electrolube CG60 would be ideal.But under no circumstances do you want an electrically conductive grease, as that would short out tracks on the PCB switch!

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 22, 2025, 10:41:24 pm
content: Quote from: mqsaharan on August 22, 2025, 04:56:00 pmAt the moment, I only have silicone oil, and since it's too thin, it's not adequate.Thanks for the photos. Yes, that screw shouldn't be tightened too much; I think it would bend the contacts! Anyway, I'll disassemble the multimeter soon and double-check how the small screw works.Quote from: tooki on August 22, 2025, 06:31:32 pmI noticed the screw later, so since I have a selector that often caused problems with mode selection, I wanted to try cleaning the old grease. Just to see if that could be the problem. I don't have any suitable grease at the moment (I only have Vaseline, but I don't think it's suitable). As you rightly said, obviously the grease doesn't have to be conductive; thanks for the two products you suggested. Curious: since it's non-conductive, won't it limit the selector's contact signal?

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 23, 2025, 01:32:11 am
content: I'll add the test I did this evening on the self-tapping screw that screws into the selector: as you can see in the attached photo, the selector pin, where the female thread is, has a circular part with a diameter of 3.5 mm that fits perfectly into the hole in the PCB. In the second photo, in the upper image, you can see that when the board is screwed in (except for the selector screw), the selector pin remains too low. If I press with my fingers between the board and the selector, the screw reaches approximately flush with the PCB, which is what the screw should do. But by spinning freely in the thread, it doesn't do its job, and so the selector remains 1 or 2 mm too far from the board.Unfortunately, I don't have self-tapping screws that small at home (this one has a diameter of about 1.8 mm, mine start at about 2.5 mm). I'll see about ordering a set of screws of that diameter, but 3 or 4 mm longer; This is only 6mm of thread, then calculating the thickness of the PCB and the plastic washer, it goes to work about 4mm into the female thread.

author: mqsaharan
author_rank: Regular Contributor
timestamp: August 23, 2025, 08:58:01 am
content: I am going to repeat a few things from my previous replies.Please refer to the attached picture.The stand offs, I talked about in one of my previous posts, are encircled in red. These will not allow your meter's PCB to push down further than a preset distance. Also, they help align the PCB in the top shell.The green arrow is pointing towards the wiper housing which shouldn't be stuck in the selector in the top shell. Please remove it so that you can install it on the PCB and adjust its height better. May be it is better to rub little silicone oil on its knob to keep it free from getting stuck again.The area of wiper contacts encircled in blue are the parts that slide on the PCB. You need to clean these as well. There is no need to put lube on these. They'll get lubricated by the lube present on the PCB tracks.Please do not try to measure the gap between the wiper housing and PCB from the back side where the screw will be installed as is shown in your last picture. You need to remove the wiper housing from the top shell so that you can physically see the gap (as is shown in the 3rd picture of my previous reply) while screwing it to the PCB. Keep that gap below 1mm, I guess. You'll be judge of it.

author: tooki
author_rank: Super Contributor
timestamp: August 23, 2025, 10:59:15 am
content: Quote from: DisasterNow on August 22, 2025, 10:41:24 pmFYI, in English, “doesn’t have to be” means “is not required, but is optional or permissible”. It does NOT mean “prohibited”.In this case, the grease must be non-conductive (=it is prohibited for it to be conductive).The pressure between the contacts basically shoves grease away at the microscopic level.Vaseline is not the very best, but is actually not terrible.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 23, 2025, 12:25:01 pm
content: Quote from: tooki on August 23, 2025, 10:59:15 amThanks, Tooki. The Vaseline grease I have at home might also work, just a very light layer, obviously. I'll try that.Quote from: mqsaharan on August 23, 2025, 08:58:01 amThanks mqsaharan. I'll have to check this evening; I think the wider cylindrical part where the screw fits also rests against the PCB on the contact side. I'll remove the selector (you're right, I haven't done it yet), but I still need to order suitable self-tapping screws; the original one no longer fits in that thread. I want a 10 mm long M1.7 screw (I prefer not to use a larger diameter; I don't want to break the female thread area).

author: J-R
author_rank: Super Contributor
timestamp: August 23, 2025, 09:05:26 pm
content: I don't think Vaseline is a good idea. It's both too thick when cool and too thin when warm, among other issues.I would suggest SuperLube, either the grease or oil, or CRC 2-26 precision lubricant.Apply the lubricant sparingly. The DMM originally has such large amount most likely because it's quicker to just brush the PCB than to apply it in a meaningful manner.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 23, 2025, 10:17:31 pm
content: Thanks j-r for the comment.This evening I applied Vaseline grease (you can see the tube in a photo, CFG brand). We'll see how it works over time. Meanwhile, everything seems fine.I put a little grease on a sheet of paper and rubbed it on the contacts, not too much (you can see it in the attached photo). To my surprise, the small screw now grips the female thread. I tightened it so that the contacts are nice and tight on the PCB, but not too tight.