Extech EX470 Multimeter - Page 1
Forum section: electronics / repair

author: uv_man
author_rank: Newbie
timestamp: July 08, 2016, 05:40:24 pm
content: G'day Mates!I've got anExtech EX470 Multimeterthat I'd like to repair. I think I accidentally had too much voltage & current across the input terminals when switching from AC VOLTS over to the HZ setting (I guess I should have unconnected the DUT before switching to HZ). Anyway, the unit still works, but the MOV is krispy black, so I can no longer read what it says (value wise). The plastic case near where the MOV was located melted a little bit too (inside), but that shouldn't really affect performance. Anyone out there in Dave-land have an EX470 that they've torn apart or know what flavor (value/specs) of MOV I need to replace? Extech doesn't provide schematics with their meters, so I have no clue as to what MOV they used. I would be eternally grateful to anyone that could offer some assistance.uv_man

author: janoc
author_rank: Super Contributor
timestamp: July 08, 2016, 08:15:08 pm
content: Mine has only one MOV that I can see - a blue one on the removable daughter board with the fuses.The markings are:VDR07D270KIt seems to be this part:http://www.digikey.fr/product-detail/fr/MOV-07D270K/MOV-07D270K-ND/2407525Seems like a 27V/250mA MOV.

author: retiredcaps
author_rank: Super Contributor
timestamp: July 08, 2016, 08:27:25 pm
content: You can remove the MOV and test your meter to see if DCV and ohms work. If it does, then get a replacement MOV. If it doesn't work, you may have fried the main IC?

author: janoc
author_rank: Super Contributor
timestamp: July 08, 2016, 08:28:24 pm
content: Quote from: retiredcaps on July 08, 2016, 08:27:25 pmWell, he did say "the unit still works".

author: retiredcaps
author_rank: Super Contributor
timestamp: July 08, 2016, 08:36:04 pm
content: Quote from: janoc on July 08, 2016, 08:28:24 pmWorks can be interpreted in many ways. It may power on and be reported as "works". Usually if a MOV is crispy black, it will affect the readings in some way. For example, the DCV could be way off.Here is an example of a Fluke "working", but it measures incorrectly.https://www.eevblog.com/forum/testgear/fluke-87-v-mystery-low-impedance-input/There are many more examples of the same when a MOV goes bad. In addition, with only 1 post from the OP, I have no idea of his level of expertise so asking/confirming that the meter measures DCV and ohm properly, to me, would be a suitable suggestion.

author: janoc
author_rank: Super Contributor
timestamp: July 08, 2016, 09:16:49 pm
content: Well, my experience with the 470 meters was that they perform poorly even when "working". I had two - the one I have sold already was constantly measuring too high on the temperature ranges, regardless of whether I used the probe or the PIR sensor. The second one I still have and that one is mostly dead as a dodo due to a faulty range switch, straight from the store. The manufacturing quality of these meters really leaves a lot to be desired, especially for the price.

author: uv_man
author_rank: Newbie
timestamp: July 09, 2016, 12:31:29 am
content: Thank you for all the helpful advice/suggestions. I was able to successfully remove/unsolder the old MOV and then perform some quick tests. On DC VOLTS I checked an old 9 volt battery and it measured 8.80 volts which looked reasonable since that is what another known good dmm measured it as.The link for the MOV replacement at Digikey unfortunately turned out to be for the French version of the Digikey web site and the part listing was "non-stocked". No worries though...I was able to find the 07D270K MOV in-stock on Mouser for only $0.12/ea.So far this meter has worked well for me. I understand what you are saying about the poor performance of the EX470 meters manufactured of late... accuracy and repeatable measurements leave a lot to be desired. That's one of my motivations for repairing this unit.Anybody care to know what Extech would charge to repair a 6 year old "out of warranty" EX470 meter?Flat rate repair fee = $100Return shipping and handling = $20...plus the shipping cost to send the meter in to Extech.If I had any reservations about this repair, the meter would be heading to the trash can 😭 and replaced with something better.

author: janoc
author_rank: Super Contributor
timestamp: July 09, 2016, 11:06:12 pm
content: Jeeze, that would cost more to repair than getting a new meter. Certainly more than the Brymen Dave is selling - and that is a much better meter than the Extech 470, IMO, even though it doesn't have that IR thermometer (IR thermometer is maybe a $15 on eBay).Sorry for the French Digikey site, I thought it will send you to the US one. They ship everything from US anyway. I wasn't able to find that exact MOV model stocked, it seems to be an obsolete part. Good that you have found one.BTW, both my Extechs were not really "recent" - I had them for several years now too.

author: uv_man
author_rank: Newbie
timestamp: July 11, 2016, 05:27:50 am
content: Was able to find a great deal for the 07D270K MOV...Amazon had it for $0.19 ea plus $2.49 S&H...plus the part manufacturer is listed as Bourne's...and it's a US seller. It's only going to take a week or so to get here (not a month or more from HK or Shenzhen China). Mouser and Digikey both had small order charges of approx $7.99 tacked on to my order. eBay had a few listings for this part but the manufacturer listed wasn't one I was familiar with (it wasn't Bourne's) and it would have come from China. Thanks again for your help.

author: janoc
author_rank: Super Contributor
timestamp: July 12, 2016, 07:50:52 pm
content: You mean Bourns. If there is "Bourne", "Bourne's" or anything else, it is most likely a fake, especially if it is coming from Amazon and not a major component distributor. Bourns components are faked a lot, mostly potentiometers and trimmers, though.