UT61E vs Ionizer

[001]

all the resistors have the values on them - just check everything.

btw,
on another forum there was a guy with a fence-charger.
he "tested" it with a fluke87 and killed it - no surprise really.
if you can kick a cow over a mile from the device via damp soil and a fence the energy must be pretty nasty.

what was funny, he then "tested" it with a uni-t mini meter and it displayed 3KV!!!!
i dont know if that was the true voltage but it didnt kill the meter 

Once  I checked TV tube with unit like Harbor Freight
And it says 1300 DC without damage

[hgg]

all the resistors have the values on them - just check everything.

I thought these resistors were internal to the IC.
Which ones are you referring to?

[stj]

i'm saying - CHECK EVERYTHING.

[joeqsmith]

all the resistors have the values on them - just check everything.

I thought these resistors were internal to the IC.
Which ones are you referring to?

They are.  Your 48 ohm resistors is another tell tail that the control IC has seen better days.   

[hgg]

Hmmm.  The chances of reviving the meter are going down by the minute...
Its also very difficult to source this IC.  It looks like that although only one
diode (from the two in the switching package) was zapped, both FC1 & FC4
were damaged inside the IC.    After installing external resistors to ground,
the modes are ok, but mV, V and Ohms do not work.  V mode flashes like it
changes every half a second from one mode back to V, mV does the same
but extremely fast and displays OL and Ohms does not measure anything.

[joeqsmith]

There have been people on these forums that have spent a lot of time trying to revive a low cost meter like this.   

I typically test the meters to failure and will have a quick glance to see if they can be repaired.  That is one of the things I see with the better class of meters.  They have enough protection that normally the controller ICs are not damaged and I am able to repair them.  The lower class of meters, it's rare I can do anything besides recycling them.   

[cdev]

What can be done to preemptively mod the meter so it wont be as susceptible to damage, and does it reduce its accuracy?

Backlight- not so important to me - durability- important to me.

[joeqsmith]

The best thing you could do is buy a better class of meter to start with if you are playing with HV's like the OP is.   The worst thing you could do is to modify a safety device in any way.

That said, it may be possible to use something like I show in the following video.   
https://youtu.be/bj_YndfA4Qs

[MosherIV]

What can be done to preemptively mod the meter so it wont be as susceptible to damage, and does it reduce its accuracy?

Add the MOVs, they are marked on the PCB but have not been installed. Not sure if it will totally protect the meter. They should clamp the input voltage in case of an over volt.

I have done it to my ut61e. The only measurement it have affected is the capacitance.

Joe has done some tests. The MOVs he tested did not give total protection to the meter. It did survive some over voltage if I remember correctly.

[joeqsmith]

You are correct that adding the MOVs would have never saved my meter from the piezo gas grill ignitor.  The nature of poor UNI-T designs I'm afraid.  I made a few videos showing the problems and how I addressed them.  As you suggested, I did run several transient tests after making the changes to demonstrate them. 

Just to be clear, while it was mentioned in that video and others, when you start dealing with waveforms in the ns with rise times in the ps there is a lot that will come into play.  Just sprinkling parts onto a board may not prove to be effective. 

[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]

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

Have you tried something like that?

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.   

[stj]

so how much did the chip cost?

[hgg]

It was kindly provided and shipped free of charge from CyrusTek.
1000 Thanks to CyrusTek

[stj]

nice, they should open a store on AE.