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Dental KavoInExam - Kodak 2000 - No Xray - solutio #70774
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RRadev Offline OP
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Hello!
Dental X-ray Kodak 2000, sometimes KevoInExam factory has a problem with the internal voltage divider of kV for feedback in the HV tank. Interrupts the bottom resistor /cold solder/.
Must be measured 10k yellow cable and black /ground /. If not have Xray exposion, and not measure the resistange you have this problem. The easy solution is new tube tank.
For the experiment could add between 10-80 kilohms between yellow and black cable, but it will not be correct feedback to determine rays can even burn tube.
The decision was invented by Neven Bekriev and consists in the use of virtual grounding scheme.
Samples were other options but this is best employed. Such as shunt resistor 200ohm between yellow and black, and amplifying the signal.

Attached Files
IMG_20160705_125002.jpg (616 downloads)
Ugly but working!
IMG_20160705_133213.jpg (612 downloads)
Ugly but working!
Kodak 2000_KevoInexam_no_XRAY_solution_internal_voltage_KV_divider_solution.GIF
Last edited by RRadev; .
Re: Dental KavoInExam - Kodak 2000 - No Xray - solutio [Re: RRadev] #70777
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Geoff Hannis Online content
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"Virtual ground" - that takes me back a few (many) years, Radoslav. Nice one! smile

This is a very interesting post; I've looked at it a couple of times, but I'm still not sure what you're advocating here.

Was (is) this a repair, a experiment, or a means of testing the circuit?

I'm guessing that the circuit diagram shows the preferred solution. Am I right in assuming that the second .jpg corresponds with the circuit? Otherwise, what is the first .jpg showing?


Re: Dental KavoInExam - Kodak 2000 - No Xray - solutio [Re: RRadev] #70782
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First picture shows from where we get pulsing voltage with 10V amplitude to making negative power supply for operational amplifier.
Second picture shows montage of sheme.
When the defect with the interruption of down HV divider to appear - put this scheme , because of down resistor sometimes makes the electrical connection /after hitting tube :)/. After about a year the cold solder is graded to "no contact". And the sheme is removed, place 10-13k resistor between yellow cable and ground. 70kV is about 3.5V from divider.

Re: Dental KavoInExam - Kodak 2000 - No Xray - solutio [Re: RRadev] #70783
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RRadev Offline OP
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This solution has been tested on more than 20 machines. It allows you to use the full life of the tube.

PS
We tried to recycle this tubes, but it is very difficult breather. Problem resistor comes from some swelling plastics - usually after the second / third year.

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Re: Dental KavoInExam - Kodak 2000 - No Xray - solutio [Re: RRadev] #70784
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Geoff Hannis Online content
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OK, thanks for that. smile

So I'm guessing that you can't get at (access) this interesting resistor, then; buried in the tube-head, or some such weirdness. think

But if you're doing that many, maybe the next step is to make a nice little circuit board!

Re: Dental KavoInExam - Kodak 2000 - No Xray - solutio [Re: RRadev] #70798
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When i see Error 13 on Kodac 2000/2100/2200, first i measure the kV feedback resistor. On KavoInExam no error, but no radiation.
I hope Kodak have start doing better HV tanks.

Re: Dental KavoInExam - Kodak 2000 - No Xray - solutio [Re: Geoff Hannis] #70816
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Originally Posted By: Geoff Hannis

maybe the next step is to make a nice little circuit board!


You could try these guys, for example. smile

Re: Dental KavoInExam - Kodak 2000 - No Xray - solutio [Re: RRadev] #74203
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Dear RRadev

My wife has the same problem with one of her 4 Kodak 2100 X-ray machines.
If the problem is that common, more of them are likely going to fail later.

I would like to create a small printed circuit board for easy installation and share it here in this forum.

But I have a couple of specific questions I need to ask before I start.

1) Is the feed back voltage (yellow wire) negative? (Is the negative power supply needed?)
2) Does the schematic show all components? No ekstra 200 Ohm shunt resistor (mentioned in your text)?
3) What is the value of the inductor?
4) I do not have the specific TL082 op amp in my inventory. Are there any specific demands to the op amp that my standard LM358 cannot fulfill? (if so, I will have to order it)

I will design a very small PCB also containing the negative power supply so it will only need to be connected to Ground, +12V and of course signal in and signal out.

Thank you in advance


Bent Erik Thomsen
Electrical Engineer
Denmark

Re: Dental KavoInExam - Kodak 2000 - No Xray - solutio [Re: Bent Erik] #74209
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Geoff Hannis Online content
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Radoslav hasn't been on here for a while (nearly three years). frown

Maybe Huw has his email address? think

Re: Dental KavoInExam - Kodak 2000 - No Xray - solutio [Re: RRadev] #74232
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Malcolm Online content
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Stinks of built-in obsolescence to me, good to see the techy types rather than Kodak are trying to resolve the issue.


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