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Discussion Starter #1
Has anyone fiddled with their 919 meters?
Ours was bought new by my grandparents, was updated later to the larger diameter cell. And that was probably 30 years ago, never been in for any work since...
Yesterday we turned it on and the needle isn't moving like normal, to calibrate or even when testing the needle wont go below half scale ..
And is not as touchy as usual.
I opened it up and it still is equipped with vacuum tubes.
They seem very simple internally and just wondered if anyone know anything technical about them.
I imagine it could be something as simple as a popped resistor or capacitor??
Maybe even a tube?
I found how to test a tube online, havnt done it yet... [trying to combine peas right now]
But I'll dive into it on a rain day.
Thx
 

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Different area than you guys. Have had ours in for service a couple times. Both times was the same thing. I can't remember what it is now. The guy at Agassiz Seed and Supply in Fargo said it was caused by brown outs. If it's plugged in and the power flickers it does it. It sounded like it was something simple. If you call a place that repairs them they might be able to walk you through some troubleshooting.
 

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Discussion Starter #4
I was hoping to send it away as a last resort... I have another that I verified accuracy today that we can use... I just enjoy fixing stuff myself. It's how I learn.
With the number of these testers out there I was sure someone who understands electronics a but better than I do would have played with one...

Heres a pic of the wizardry inside of an old original one if anyone has ever wondered...
20190916_210543_1568692226715.jpg
 

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When was it used last? I am putting money on the potentiometers oxidized up after sitting, even for the season. Grab yourself some electrical contact cleaner and spray it on the pots working them back and forth. Just make sure to let everything dry before putting power to it. Isopropyl alcohol can be used to, just don't use anything like wd-40.
 
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10 years ago a new needle and calibrate was almost cost of new, i got 3 dead ones that can stay that way.
 

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Discussion Starter #7
When was it used last? I am putting money on the potentiometers oxidized up after sitting, even for the season. Grab yourself some electrical contact cleaner and spray it on the pots working them back and forth. Just make sure to let everything dry before putting power to it. Isopropyl alcohol can be used to, just don't use anything like wd-40.
I dont think there's any pots in this vintage of a unit... other than the 2 between the vacuum tubes [which I assume are for fine calibration, which I dont want to mess with yet]
The dial and external calibration knob are a non contact type.... I believe they're a capacitive variety.
They have metal discs that do not touch but Introduce more surface area as they're adjusted.

10 years ago a new needle and calibrate was almost cost of new, i got 3 dead ones that can stay that way.
I searched online and found a company that will upgrade to full digital for just under $600, a new one is about double that these days I believe.
 

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Last time I talked to the guy at Dino's, he said he was swamped with guys that had went digital and wanted them switched back... not sure what the reason was but he said "too many issues." I almost bought the Ag Days special from him a few years ago, but ended up with one from an auction sale that has been working so good I've never had to touch it.
 

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What I did was go digital, with a few cal was over 900, plus no one told the ahole to change it.
 

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Discussion Starter #11
That's good to know about the issues with digital... I was awfully tempted to go that route if I couldn't find a solution my self.. but this makes me want to keep it as original as possible... after all the thing is older than me and worked so good, for so long...

Besides the digital issues mentioned I really didnt want to send it away because it has the original old ound needle meter on the front, I think they just look so cool, and I hate the looks of the new plastic square ones.

I suppose checking the vacuum tubes is the next logical step, i read online they should be warm... neither one is on mine but when removed, the needle fails to move at all, so they are doing something...
They don't rattle and are not discolored.

What's the chance someone would have a wiring schematic for a 919 with vacuum tubes?
 

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I may have vacuum tubes if you find out that is the problem. Uncle used to repair tvs back in the day. What is the brown part on the tube side? I assumed that was a pot.
 

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Discussion Starter #13
The round brown part in the pic is the operation/calibration switch.
I tried searching those tubes....
Most info is now all about sound amplification....
I sent off an email to a tube supplier company giving them the numbers and with any luck they can decode or even supply me with new ones.
I suppose I'll just replace them if they're not too spendy.
But I still should try to test them if I can, at least for my own knowledge.
 

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I agree, clean your switches and potentiometers. Tubes degrade slowly over time and if the heater goes, its obvious. All the 919 does is compare the chamber to a known capacitor value using a frequency around 250 khz thru a wheat stone bridge. When you turn the dial, you are changing the resistance of the Resistor/Cap circuit opposite the reference R/C. When they are the same, the circuit nulls (zeros out) and that is when you read the lowest value. The value on the dial (resistance) is used on the chart to show the equivalent moisture at that capacitance.



Old electronics are problematic, caps will drift, tubes get weak, contacts get oxidized, pots rub off their graphite. Best to just replace it, and put that one on the shelf for memories.


If you would like to read more about capacitive reactance - https://www.electronics-tutorials.ws/filter/filter_1.html So all a moisture tester is is 2 of those circuits and the dial tries to make them the same. Yes, that 2000$ meter is an oscillator and a couple resistors and a capacitor.
 

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Discussion Starter #15
I haven't had the opportunity to check the vacuum tubes yet, but I reached out to an online company i came across [Vivatubes.com] that specializes in vacuum tubes.
I e mailed a description of the tubes in my tester and was told they are both the same tube.
The tube type is DF92/1L4.
I went on Ebay and found a matched set for $9.00. So I just ordered them.
Since I learned they are both the same tube, this leads me to believe I have at least one failed, because I swapped them and it made the needle move the opposite direction... if they're both the same there should be no change.
I'll keep my results posted for those who are interested.

I'm determined to fix this old gurl.
 

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Discussion Starter #17
Well the vacuum tubes i ordered off Ebay arrived! I think i ended up spending $25 to $30 In total for the "matched pair" of American Navy tubes. 20191004_143152_1570316458839.jpg
Stuck them in place, and, it works!!
I did a whole bunch of side by side tests with the other meter we have and I found it to be a little inconsistent when first powered up [I think this is due to the vacuum tubes needing time to warm up??]
But after powered up for half an hour or so it was within .2% compared to my other tester.
I checked canola, wheat, oats at varying moisture levels all within .2 sometimes right on.
I also noted that even dumping from one tester to another and back again you can expect varying results.
I'll most likely try to get a few samples one quite dry with a low dial number and one tough with a high dial number and verify at the elevator to know for sure, and for peace of mind.
20191004_194239_1570317374592.jpg

So in conclusion if you have an older 919 meter that all of a sudden the dial will not go below half scale when attempting to calibrate, chances are you have a bad vacuum tube.
 

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:3::3::3::3:Now where are you going to find a really dry sample to test it out this year????????!!!!!!!! If you want some really tough $hit to see how high your meter will go, I can help you out with that!!
 
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Discussion Starter #19
Definitely easy to find tough stuff around here too this year.... only dry stuff is coming out of the dryer... ?
 

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The 919 is still the farmer choice but the Canadian Grain Commission allows the use of the following machines/

Industry Services will determine the moisture content of grain with a Unified Grain Moisture Algorithm (UGMA) moisture meter or with a Near-infrared transmittance (NIT) instrument. CGC staff should refer to National work instructions “IEQ-3 – Moisture Meter – Model 5200-A” or “IEQ-2 – Moisture Meter – 919-3.5”
 
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