Author Topic: Restoring Display flex on an old Micronta 22-191?  (Read 3849 times)

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Offline reagle

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Restoring Display flex on an old Micronta 22-191?
« on: December 30, 2015, 01:30:32 pm »
So it started innocently enough with a teardown (http://kuzyatech.com/micronta-22-191-multimeter-teardown), but then I just had to unscrew the display holder. Of course the paper-thin display flex tore off the board. Does anybody still even make these things? I suppose one option is a wide regular flex, with a strip of Z-tape on each side?



Offline ModemHead

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Re: Restoring Display flex on an old Micronta 22-191?
« Reply #1 on: December 30, 2015, 05:10:34 pm »
I fixed one a couple years ago, another example of "extreme repair" where the unit isn't really worth the time, it's just the fun of getting it to go again.

I used Goof-Off brand cleaner and some Q-tips to remove the coating from a fresh section of what appeared to be graphite traces, then cut the damaged end off.  Thoroughly cleaned the landing pads on the PCB.  From scrap plastic I made a piece that would compress the end of the flex tightly onto the board when the LCD bezel is screwed down.

And it worked!
 

Offline AlphZeta

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Re: Restoring Display flex on an old Micronta 22-191?
« Reply #2 on: December 30, 2015, 05:18:59 pm »
You could use conductive glue (e.g. silver based) for that. I did a few similar repairs like that before (not totally torn off though).
 

Offline krivx

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Re: Restoring Display flex on an old Micronta 22-191?
« Reply #3 on: December 30, 2015, 05:25:36 pm »
If the cable is Polyimide you can solder it. Here's a similar repair http://www.projectvb.com/displayfix.html#Solder

You can test if this will work by touching one of the damaged corners with a hot iron and see if the cable substrate can handle the high temperature.
 

Offline TAMHAN

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Re: Restoring Display flex on an old Micronta 22-191?
« Reply #4 on: December 30, 2015, 05:32:01 pm »
First of all, restoring something always is worth the effort - at least for me. I recently repaired a 25 bucks WiFi extender (which actually is quite crappy from its IPv4 performance) - for fun and kicks, and to see how it was built up and to learn tricks.

Now, please do not beat me. But IMHO, I would not bother with the paper display. Grab an SMD AVR and one of these tiny "won hung lo" oleds from AliExpress, and hack up a "display + data logger unit" of your own. But that is just me, of course - who is currently ripping out the nixies from a SystronDonner 6153 to replace with a similar contraption.
Feel like some additional tamile wisdom? Visit my YouTube channel -> https://www.youtube.com/user/MrTamhan for 10min tid-bits!
 

Online Fungus

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Re: Restoring Display flex on an old Micronta 22-191?
« Reply #5 on: December 30, 2015, 06:30:25 pm »
Conductive glue sounds good...
 

Offline reagle

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Re: Restoring Display flex on an old Micronta 22-191?
« Reply #6 on: December 30, 2015, 08:39:49 pm »
I like ModemHead's idea- will try that first. The substrate looks to be of a low melting temp, so soldering is not really an option. Plus traces are carbon ink- cheap bastards :)

Offline retiredcaps

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Re: Restoring Display flex on an old Micronta 22-191?
« Reply #7 on: December 30, 2015, 11:16:54 pm »
I received one of these meters for free about 4 years ago and it suffered from the same fading lcd.  I also noticed it was the only meter, out of 50 or so that I have used, that was out of calibration.   It was 1.1% out on DCV.  A quick turn of the pot fixed it.  The date code on the 22-191 indicated it was made in 1987.

I won't embarrass myself with my attempted repair, but I did send it off to another fellow in the UK and he managed to repair it.  He is a huge fan of this meter.

He used "Spring steel and bodgery".  These are his pictures that he sent me of the repair.  His repairs pre-date modemhead's repair.

PS. Just read through the blog entry and meters, working or not, that use AA for $1 always have a place in my home.
« Last Edit: December 31, 2015, 12:34:25 am by retiredcaps »
 

Offline reagle

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Re: Restoring Display flex on an old Micronta 22-191?
« Reply #8 on: December 31, 2015, 03:45:28 am »
Thank you everybody for the ideas- I feel I have a good chance of fixing it, plus I now have a bit more motivation to do that after seeing what others have done :)
It may end up being a combination of methods- I'll dissolve some of the paint to get to conductive traces, and then maybe try Ztape to actually attach flex to the board.
As far as the AA powered meters, the best in my collection is the Hioki 3200-50. 1984 date code, built to almost Mil-STD!

 


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