Electronics > Projects, Designs, and Technical Stuff

UT61E vs Ionizer

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hgg:
In the case of high voltage low current, the UT61E is vulnerable at is FC lines
that connect directly to the main IC.

The board has test points for each of the FC lines.

What about if we use something like the following to each of the line, and especially before the
switching diode D4 ?  They are very fast and go up to 8kV.

https://www.onsemi.com/pub/Collateral/ESD7951S-D.PDF

hgg:
Just an update.

Today I found the courage to try to repair the UT61E...
After a long and nerve wracking soldering session, I've removed the main IC and replaced it with a new one.



The UT-61E came back from the dead and works perfectly fine!   :-+ :-+

I used one full Rossmann unit of flux for soldering.. and while it was soldered fine, its a PITA to clean
the flux afterwards from that type of package.  An ultrasonic cleaner will be the next purchase I think.

It was indeed the main IC that got zapped.   No clamping diodes, no other component, just the IC.
Its FC lines have no protection whatsoever from electrostatic discharges and I think that this was
what killed it.  I will order a 4 channel ESD diode IC to clamp all the FC lines.

I've also replaced the voltage calibration pot with a 2K Bourns.  A 1K would have been a better choice
since only two legs are connected and the resistance when calibrated is around 565Ω.
I've also cleaned and greased the rotary switch contacts and its back in service as new!   :)

I know, its a cheap meter but I am sure that everybody knows the feeling when you bring back
from the dead a piece of electronics equipment, especially if you have been using it a lot and also
made a lot of mods.  Cheap stuff and things that do not work optimally is the best way to learn!

Thanks for the help.

joeqsmith:
If you read the datasheet, there is a reason they do not clamp it.  Too much leakage.  I did show in the video how I addressed this.   

hgg:
The following is advertised for low leakage :   (100nA)
https://www.onsemi.com/pub/Collateral/NUP4004M5-D.PDF     

Have you tried something like that?

joeqsmith:

--- Quote from: hgg on May 01, 2019, 02:40:06 pm ---The following is advertised for low leakage :   (100nA)
https://www.onsemi.com/pub/Collateral/NUP4004M5-D.PDF     

Have you tried something like that?

--- End quote ---

Easy enough to calculate the error it will cause and see if that's acceptable to you. 

No, I only tried what I showed when I made that video.   

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