AN8008 very high resistance reading - Page 1
Forum section: electronics / projects

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 28, 2017, 01:46:15 am
content: So I had this DMM in storage since a few months. Needed it last night and the continuity function simply didn't work. In resistance mode it read about 120 ohms with the probes shorted together. After a few cycles of reinserting the probes, and cycling the rotary switch it worked again.Today it went back up to 12 ohms, pressing on the dial in ohms mode changes the reading a lot.Is this common with this unit? No other meter I've ever had did that.

author: danadak
author_rank: Super Contributor
timestamp: December 28, 2017, 01:58:22 am
content: You in a high humid environment ? Or a smoker. Or use awoodstove.....Sounds like rotary switch contact interfaceneeds cleaning.Regards, Dana.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 28, 2017, 02:12:35 am
content: It's new. No smoking. It's like 20% RH here in winter. None of my other DMMs do this. Tektronix DMM249 in same conditions works great and it's like 20 years old.Even the AN860B+ works fine.

author: floobydust
author_rank: Super Contributor
timestamp: December 28, 2017, 04:01:40 am
content: I have the same problem- the AN8008 rotary switch is a piece of shit.If I don't use the meter for a week, I get flaky operation until I spin the rotary switch a few times.I've cleaned and lubed my switch a few times, it's low humidity here <50% but it's still unreliable.The PCB is gold but the wipers are some cheap copper that oxidizes very easily and has a tiny contact point.I think the fix is to electroplate the wipers with a noble metal.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 28, 2017, 10:12:55 am
content: Thanks. I think the fix is a trip to an e-recycling bin.And a warning to others.

author: floobydust
author_rank: Super Contributor
timestamp: December 28, 2017, 04:34:49 pm
content: It was so bad I thought they used spring-steel for the rotary switch wiper, but I found it non-magnetic.Copper oxide is semi-conducting and really the worst thing in a multimeter. Steel would have been betterIt's almost land-fill grade, just get used to a rotary switch spin session before using it, and in the middle of measuring something you might have to spin again.

author: GreyWoolfe
author_rank: Unknown
timestamp: December 28, 2017, 04:49:08 pm
content: Interesting experience. I've had an 8008 a couple of months now. It sits in my company van tool bag. Florida is humid all year round. I just got an 8009 as a back up and I compared resistance measurements for my work purposes on both meters and both read the same. I didn't do a continuity check as that is something I probably won't have a need to do, just low resistance measurements. I guess I should exercise the rotary switches on both of them regularly to avoid the same issue from cropping up.

author: Kalvin
author_rank: Super Contributor
timestamp: December 28, 2017, 05:06:52 pm
content: I have two AN8008s meters and both of the require some "dialling" if I haven't used them for a while. Poor design, but I am fine with the feature now that I know it.

author: floobydust
author_rank: Super Contributor
timestamp: December 28, 2017, 05:16:35 pm
content: Rotary switch lube can keep the contacts from oxidizing, so I think this is why some people are not having issues... yet.The lube is typically mineral oil in multimeters, but there have been many battles here over lubes, sometimes leading to religious fighting and flames:https://www.eevblog.com/forum/reviews/question-dmm-grease/https://www.eevblog.com/forum/beginners/lube-dmm-selector-switch/https://www.eevblog.com/forum/repair/multimeter-or-oscilloscope-hv-safe-lubricants/Florida is so nice and humid, so I thought worse problems.P.S. if you take the rotary switch apart, the detent spring and balls want to shoot across the room, so watch that.