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UNI-T UT61E Multimeter teardown photos.

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honeybadger:
joeqsmith: in ES51922 datasheet there is:
Most of pins are protected by the ESD protection circuits. However pins, V+, V-, AGND, DGND and
VR1 are not protected enough because the parasitic effect must be decrease. Therefore enough external
protection is needed for assembling, carrying and keeping. In addition, components connecting to these
unprotected pins have to be soldered on board before the IC is soldered.

I just wonder. There is no PTC... nothing. When the 10M resistor fails (or more probably any of the capacitors around) the current will go straight to the IC.



joeqsmith:

--- Quote from: honeybadger on April 01, 2019, 11:21:31 am ---joeqsmith: in ES51922 datasheet there is:
Most of pins are protected by the ESD protection circuits. However pins, V+, V-, AGND, DGND and
VR1 are not protected enough because the parasitic effect must be decrease. Therefore enough external
protection is needed for assembling, carrying and keeping. In addition, components connecting to these
unprotected pins have to be soldered on board before the IC is soldered.

I just wonder. There is no PTC... nothing. When the 10M resistor fails (or more probably any of the capacitors around) the current will go straight to the IC.

--- End quote ---

That's a VERY good point.  Consider that for DC the capacitors are an open.  Apply a fast transient, like ESD, and they will pass it right on through.   In this case, adding the MOVs won't help.  They may have a fair amount of capacitance but the inductance seems to dominate at these higher frequencies.  No real surprise.   

The PTCs and surge rated resistors are there to limit the current through the clamps.  The problem I see with the 5mm parts is they will break down.   

I made a video some time ago showing all of this on the 61E which includes the part of the document you posted.   I basically walked through the problems and explained a few ways to attempt to improve it.   Sadly, most viewers had little interest in the theory.   I've added a link.

https://youtu.be/cMutvk_6xhY?list=PLZSS2ajxhiQDrk4o1Y45auwK7LomjnNBU

DiddlyJackSquat:
If anyone has been chasing my thread about my faulty UT61E here's the gist...
Have issues with it powering on but no beep and the screen goes blank?
reflow the IC and it is revived momentarily?
Check the ecaps on the other side of the board (the battery side) for leakage or... just replace them. piece of crap leaked a little. can't imagine what would have happened if i saw it later. I replaced them with through hole in a method I call "through hole surface mount soldering" :P
while you're there, replace the solder on the 3.999 oscillator because that lil butt solder cracked on mine!

chasing red herrings all day long  :palm:

honeybadger:

--- Quote from: honeybadger on March 27, 2019, 01:21:19 pm ---Hi, my new UT61e just arrived and I must say I am confused about voltage ranges.

at "mV" DC range it says "OL" when nothing is connected.
at "mV" DC range it measure "0.20mV" even with terminals shorted with thick wire with gold plated banana plugs.
at "V" DC range it masure "0.0020V" with shorted terminals.

This shouldn't be happening I guess. With all my others DMMs when voltage is selected and nothing is connected it shows something but definitely not "OL" and when I short the terminals it shows something really close to zero - definitely not 20 digits above zero.

Is this enough for a warranty claim?

edit: accuracy is suppose to be:
220mV +/- (0.1%+5)
2.2V / 22V / 220V +/- (0.1%+2)

So for 220mV range it is suppose to show 0.05mV in worst case scenario -> offset is 400% off.
For 2.2 range it is suppose to show 0.0002 in worst case scenario -> offset is 1000% off.

edit 2:
It measures off by 0.4V at 30V DC. Jesus Christ how is this possible with a new multimeter?  5USD noname is more accurate.

--- End quote ---


Update:

After collecting dust for several months I finally decided to try the ultrasonic cleaner. I had an idea that there must be some leakage current somewhere to cause the offset.

After 10 minutes in ultrasound and drying with a hot air gun  ^-^ and adjusting VR1 it works like a charm!
DC voltage 0.1-30V there is a next to nothing difference to BM867s - definitely less than 0,5%, good enough.
DC current - OK.
Cap - OK.
Res - OK.
mV range will still show "OL" when not connected, but "0.00" when shorted - probably OK.

I am surprised that trimmer pots survive ultrasound without any problems.

tecnicaemail:
Hey guys, first of all I'm sorry for my English, I'm using Google Translate, today my UNIT UT61E arrived, after some research I saw that many people recommend that I put photos of it open for you to see if something has changed since 2020?  I read the 45 pages of the topic and found it interesting to put the led to light the display using the HOLD button but I was in doubt, can I ask right here?  I thank everyone.

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