Benning MM-7 not to be recommended unreliable - Page 1
Forum section: electronics / testgear

author: sphinx
author_rank: Contributor
timestamp: October 19, 2017, 11:06:02 am
content: I bought a Benning MM-7 some years ago and laltely it's become unreliable to measure with especially the diode measurement it started to show a valuewithout anything connected and after taking it apart and looking i directly saw that what most likely was the issue the tiny electrolytic caps. I took myheat gun and warmed them up one by one as carefully as i could and after a couple i saw that the display showed o.l. . So there is an issue with qualityand bad judgement on selecting capacitors for this and possibly other models as well from this brand. I was thinking of saving a bit more to get a fluke atthat time but i choose benning which now i regret so much now i got 2 Benning MM-7 and a clamp meter I can not trust anymore, so now bringing back aneven older fluke to use instead.So for this i would not recommend to get any Benning without being able to have a peek inside to look after electrolytic capacitors which most like will getworse over time and making meters unreliable, i have got a schematic for a similar measurement IC but i can not be sure that if any "elyt-caps" are in thevoltage and amp measurement chain which makes the meters not reliable to use.Regards mike

author: wraper
author_rank: Unknown
timestamp: October 19, 2017, 11:33:49 am
content: QuoteThis is virtually impossible for multimeter this new and there shouldn't be any electrolytic caps in signal path. Not to say there is no ripple current or heat to cause them fail. Also hot air is not a tool to check them.QuoteMore likely you heated something else around them. Like MLCC.

author: sphinx
author_rank: Contributor
timestamp: October 19, 2017, 11:45:09 am
content: i will try to heat them one by one with a soldering iron trying not to warm the other components around so i can be more sure if they are causing a problem or not.even if you say that this not a the right way, the values of a bad capacitor changes quite a bit compared to an ok one so it can be used to check if it's bad or not,and also measure with a capacitance meter. Try it and you will see that you can use this method to test.I just went and tried and where i warmed the capacitors one by one there were 3 in a bunch on first warming one of them nothing happened and the second oneall of sudden value jumped to o.l. and after cooling down issue is back. There is also a diode close to caps but warming it doesn't make much differencein that bunch of capacitors there is pretty empty/clear of componentsso i am very SURE that the caps are causing this issue maybe others i dont know about so these meters are not so reliable after some time.regards

author: wraper
author_rank: Unknown
timestamp: October 19, 2017, 12:01:10 pm
content: Quote from: sphinx on October 19, 2017, 11:45:09 amI have enough repairing experience to know what works and what isn't. Just measuring capacitance will show capacitor failure only if it is completely dead. Also you need to desolder them out of the circuit before checking capacitance, otherwise measurements will be incorrect. I have enough experience to tell what likely may failed, and in this case, this does not sound like electrolytic capacitor failure at all. Also there is no prerequisites for them to fail in such usage conditions, even if capacitor quality is bottom of the barrel. If you read a lot of forum like badcaps and think that vast majority the failures are electrolytic capacitor related, the truth they are not at all. This is valid for some types of devices, but only forsome, not all. Also you claimed capacitors are crap, but did not say manufacturer or at least post a photo.

author: wraper
author_rank: Unknown
timestamp: October 19, 2017, 12:04:26 pm
content: QuoteThen replace suspected part if you are sure and see how it works.

author: sphinx
author_rank: Contributor
timestamp: October 19, 2017, 01:13:24 pm
content: I replaced the suspected bad cap shown on the pictures not the best ones but it's all i got at the moment. Now meter seems to work ok indiode mode. i will order some caps to exchange them for new ones. for other measurements i can not be sure that it shows the right values.I am getting so damn tired of people telling i got so much experience this and that, and you don't know shit about this or that.And your posts were of no real value sorting this out, you should keep you experiences to yourself. The only thing you do iswanting to show off and at last you are the one that looks like an *** !i will still say benning mm-7 and maybe other meters are not reliable after some time of use due to poor choice of componentsin certian places.regards mike

author: wraper
author_rank: Unknown
timestamp: October 19, 2017, 02:08:32 pm
content: That capacitor is used in DC/DC converter. Very strange they used electrolytic capacitor, as 0.1uF capacitor is needed there according to datasheet. It would be best to use X7R ceramic or film capacitor instead. Cap between pins 95 and 96 (C+, C-)http://pdf.datasheetcatalog.com/datasheets2/90/903234_1.pdf

author: wraper
author_rank: Unknown
timestamp: October 19, 2017, 02:17:18 pm
content: Also you said it's a few years old. But main chip is made in 2000! 4013B is also made in 2000. This is either 15 year old meter or they used very old stock of these ICs.

author: wraper
author_rank: Unknown
timestamp: October 19, 2017, 02:25:43 pm
content: I noticed that AD737 is also made in 2000. Your first post is certainly misleading when describing the meter. Also complaining about failed cap after more than 15 years is sort of... unfair.

author: sphinx
author_rank: Contributor
timestamp: October 19, 2017, 02:38:55 pm
content: no further commenting

author: retiredcaps
author_rank: Super Contributor
timestamp: October 19, 2017, 07:05:47 pm
content: Quote from: sphinx on October 19, 2017, 11:06:02 amYour Benning is a rebadged Appa tech multimeter. Searching right now for the exact model ... some variation of the 90 series.edit: found it. Appa 99 II.