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Are Extech EX730 clamp-meters repairable???

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Junior Member level 1
Apr 28, 2001
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I've just fried my Extech EX730 clamp meter while developing something that used a 230V-12V transformer in reverse, and 18V on its secondary. Given that the meter is rated to 600V, I figured there would be no problem! Now I have a meter on which only the temperature and frequency functions work - everything to do with voltage is gone, INCLUDING the clamp-current options!!! Given that some functions still work, it would appear (to me) that Extech are using no buffering of any sort between the input and logic, just a direct connection. Does anyone know anything about these meters???

PS. This is my second Extech clamp meter. The first EX730's temperature function failed after just a year and was replaced under the 3-year warranty. The main reason I opted for Extech was because I then reasoned that they were of at least of intermediate quality - no Fluke, but much better than cheap Chinese meters. Sadly my experience has shown this to be definitely not the case. The reason I got the EX730 was to measure DC current. Although this has a supposed resolution of 0.01A, the practice you cannot measure anything withing a couple of hundred milliamps. And both meters were identical, so it's not a case of having got a dud! Compare that to the Uni-T UT210E I got recently. It's an order of magnitude better than the Extech when it comes to measuring current, while costing about a third the price. I also got an Extech 42530 IR meter at the same time. This piece of crap's reading wanders all over the place,right down to -50C at times - just another piece of Extech junk in my experience.

Excuse me letting off a little steam, but that meter is just a stone-throw away from being introduced to a lump-hammer... :-D

Well, I resisted the hammer-urge and went looking for info on the EX730, and hopefully a schematic, but alas, it was not to be. What I did find was **broken link removed** site, which contains lots of info on multimeters, including quite a few schematics. Also linked to is a list of multimeters that don't quite make the grade for various reasons. And no, the EX730 is not included among them, but I believe only because the 'offenders-list' hasn't been updated in a few years. What is included about Extech meters is particularly damning however;

Extech EX330 CATIII/600V CATII/1000V Current ranges have glass fuses rated for 250V with no warning of lower voltage (Submitted by T4P, reviewed by Dave Jones) Additional information and reviews on different Extechs show that Extech EX series are to be avoided in general. The quality control appears to be so bad that parts are coming loose inside some meters from the factory, amongst other problems.

The almost-certainly damaged chip in question in the EX730 is the **broken link removed** by Cyrustek. As I suspected, the voltage-in is tied (almost) straight to the chip itself, with only a 10M resistor intervening. Looking through the Cyrustek pdf, it appears this is the recommended way of doing things, and given that the pdf talks of voltages up to 4000V being applied, I still cannot fathom how a piddly little 5W 230V/12V transformer, with an 18V square-wave applied to the secondary, managed to kill it.

Nothing on Ebay, but you can buy the ES51962 on Aliexpress for about $20. No chance, not at that price anyway! I'll spring for one if someone drops the price to $10, and then only as a penance for frying it in the first place. Yep, Extech are crap.

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