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发表于 2021-12-16 14:38:40
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这个帖子有类似的问题，说是开启自动量程就有问题，关掉就正常，你关掉试试能不能用，要是能用就凑合用呗：
https://www.eevblog.com/forum/pr ... -range-malfunction/
Hello Folks,
I snapped a "defective" LCR from ebay. You may have guessed it from the topic: an Escort ELC-133A. The seller stated that it gives you FuSe for defective Fuse at a start up, but the Fuse shall should be ok.
So I got it and tried it....sure...start, a bit of autorange and then FuSe. I opened it up, the Fuse was fine and the specs of the fuse seemed fine, so I checked the solder joints. They looked fine, too.
After a bit of trying and searching on the PCB I saw that there is about 70kOhm as resistance between - and +, So there couldn't/shouldn't be a problem with a disconnected trace.
Then I found it strange that the Autorange went a bit on and on (nothing connected shurely...so I expected OL or 0) and then there was the FuSe message. So I thought, hay. Shorten up the connectors.....started it, no Problem. It was running! Hmmmm, disconnect....autorange....FuSe. Plug in a Resistor and it worked (even though it gave me a quite different reading from my U1253B) The Agilent settled at 9.922k and the Escort at 9.873k (100Hz, Ser).... try my old voltcraft DMM which gave 9.67k. It should be an 10k 5% resistor..... so technically it works.
Then I switched off the Autorange and it works!....Atorange on,...it begins to FuSe again  . So it really seems to be depending on the Autorange function.
So maybe sth. in the firmware?! Or could it be that it cranks up the measuring-current when autoranging and somebody inside says goodbye (shortcutting or so). There is also a PTC as secondary fuse as it seems. Maybe that buddy could be making trouble?!....I'll have a look.
Suggestions appreciated
BTW: Who is trusty from the three DMM's  .....three Meters and three quite different readings , but all are within the 5%. I should have a look later with another Resistor with lower tolerances.
PS: If I start the LCR and disable the Autorange it is working.....
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