Extech EX520 - DOA - Page 1
Forum section: electronics / testgear

author: Zeitkind
author_rank: Contributor
timestamp: January 11, 2018, 10:25:01 pm
content: Hiho!Got myself a new dead multimeter from eBay, an Extech EX520. I know, it's slow, it's from China and it's too expensive (~180€), but hey, the broken one was for 15€..It seems it is a customer returns from a german distributor (prob. Conrad?) because this eBay-seller sells a lot of customer returns (from cat trees to computers..). Description: something like "wrong measurement/display". The meter seems almost unused, but indeed showed wrong voltage and ohms, but not only wrong, the input wasn't connected at all (eg. voltage floating around some mV and shorting the leads had no influence). I opened it and checked some resistors around the input - which doesn't look that bad: 3 MOVs, a PTC, big fuses.. PCB version is "EX520-4", it has a Fortune Semiconductor FS9922-DMM chip (6000 counts, auto-ranging etc.). When checking the PTC I noticed that it's just broken, see picture. The coating on one side is also gone - and is not inside the meter, so it has to be broken already during manufacturing.Not really a good sign of quality control.. I checked the PTC and it measures 900,0?. I clamped the leg to the PTC with a crocodile clip - and voltage (5,000V DC) measured fine.Anyone has a decent replacement part number/model? The PTCs I have are either way bigger in size or for max. 60V or 230V with some 10?. A YS4020 or Epcos B774 with 1100??Would I buy a new Extech? Well, prob. not. A multimeter for >180€ should pass a more decent quality control, IMHO. Will I use it once repaired? Yes, but for TTL ranged voltages up to 60V...

author: wraper
author_rank: Unknown
timestamp: January 11, 2018, 10:38:54 pm
content: Quote from: Zeitkind on January 11, 2018, 10:25:01 pmI don't think it was a QC issue, probably multimeter was dropped from serious height.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 11, 2018, 10:41:51 pm
content: Quote from: Zeitkind on January 11, 2018, 10:25:01 pmThat about sums up how CEM Instruments, the original OEM, does their multimeter production.QuoteMost PTCs in meters that I have measured are around the 1k or 1.1k ohm range. So 900 ohms seems fine to me.QuoteI have written about the YS4020, but it is impossible to find anywhere.QuoteI wouldn't.

author: wraper
author_rank: Unknown
timestamp: January 11, 2018, 10:54:32 pm
content: Quote from: retiredcaps on January 11, 2018, 10:41:51 pmIt's available at digikey and mouser.

author: Zeitkind
author_rank: Contributor
timestamp: January 11, 2018, 10:59:23 pm
content: Quote from: wraper on January 11, 2018, 10:38:54 pmI don't think so. If it was after sealing/closing the housing, there should be some remains of the coating left on the PCB and inside the housing - but there is none. The PCB was clean, the PTC was "torqued bended down" the PCB to fit, the fault wasn't that obvious as it is now on the picture, I blended it up. Either someone else opened it before me and cleaned it (which is unlikely, the screws were untouched AFAICS), or it happened during manufacturing.

author: Terry01
author_rank: Frequent Contributor
timestamp: January 11, 2018, 11:10:21 pm
content: The Ex Tech meters get a bad rep! I have 1 too, the EX505! I would agree that they are not the best meter and the rep is well deserved.The only Range that is accurate is the temperature range, It's spot on!All the V & A readings are out by around 1% quite uniform through all the ranges,The diode, capacitance and continuity buzzer are all rubbish although the resistance reading is damn near spot on too in fact!I love mine though. I keep threatening to get rid of it but it's still there yet.

author: wraper
author_rank: Unknown
timestamp: January 11, 2018, 11:10:51 pm
content: QuoteI don't see why would it need be in such position to fit. If multimeter was dropped on it's lower part (or top if it was bent upwards), this is exactly what could happen. This is quiet heavy part on relatively thin legs. Dunno how it looked like originally but there is certainly some dust on PCB around the part.

author: lem_ix
author_rank: Regular Contributor
timestamp: January 11, 2018, 11:23:55 pm
content: CEM really seems hit and miss. I've got a PeakTech rebranded one and it's fine inside. As for the spare parts ... a lot of them have broken selector switches so you can get a replacement pcb cheap...

author: retiredcaps
author_rank: Super Contributor
timestamp: January 12, 2018, 12:35:15 am
content: Quote from: wraper on January 11, 2018, 10:54:32 pmI haven't checked in a few months and yes you are correct. It is stock at digikey and mouser. Thanks for the update.

author: Zeitkind
author_rank: Contributor
timestamp: January 12, 2018, 03:08:14 am
content: Quote from: wraper on January 11, 2018, 11:10:51 pmThe "dust" is from me folding the PTC back and measuring the resistance. There is no sign of the missing green coating at all.The legs are quite stiff, even a bigger shock would not bend them towards the PCB. But the legs are to long, they do not align with the holes in the PCB, they twisted and bend it towards the PCB. My guess: the legs of the PTC were also partly coated, and someone kept all the coated part above the PCB - making the PTC stand to high above the board. Bad design or wrong BOM or wrong parts. Never ever you'd see something like that in a Fluke, Metrawatt, Sanwa or Agilent. Dave made a teardown of the EX505 years ago (#99) and also noticed the PTC "crowded and folded". In my 520 the big cable running across the PCB is pinched below the HRC fuse..And, omfg.. this meter is so slooow. Even my oldest BBC meter is faster. o_O