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 Post subject: Mark 5XL repair
PostPosted: Sun Sep 17, 2017 6:55 pm 
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Location: Panama City, FL
I have a Graves Mark 5XL. The 5K potentiometer in my unit is not very linear and I would like to change it to one that has a better specification. Can someone tell me how to disassemble the potentiometer form the head unit? I can't figure out how to remove the arm for the head unit.
Thanks
Jim


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 Post subject: Re: Mark 5XL repair
PostPosted: Sun Sep 17, 2017 8:36 pm 
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Location: Florida, United States
JJ wrote:
I have a Graves Mark 5XL. The 5K potentiometer in my unit is not very linear and I would like to change it to one that has a better specification. Can someone tell me how to disassemble the potentiometer form the head unit? I can't figure out how to remove the arm for the head unit.
Thanks
Jim


Jim,
First, I suggest that you replace the battery with a fresh, new one.
That will probably fix the non-linearity issues that you observe.
Replacing the potentiometer is not quick and easy. If you truly understand how the unit is put together, you would have have at least 6 hours of machining. You are not dealing with a modular design.

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 Post subject: Re: Mark 5XL repair
PostPosted: Sun Sep 17, 2017 10:27 pm 
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Location: Perth, Australia
I bought my machine in 2012 and I think I have now a similar problem. Basically there is no good calibration, as if I set the 45 degrees angle to its correct value, the 90 degrees angle is off by about 4.5 degrees, while if I set the 90 to its correct value, the 45 is off by 2.5.
I've tried changing the battery to no effect.
I think you would need to contact Graves for this and ask them to change the pot.


Last edited by Nico D. Cero on Mon Sep 18, 2017 11:09 am, edited 1 time in total.

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 Post subject: Re: Mark 5XL repair
PostPosted: Mon Sep 18, 2017 7:15 am 
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*sigh* The original XS3 assembly is based on a life expectancy of Position Sensor MBTF: 10 Million cycles.and be 1/4 of 1% linear or better, laser trimmed. It's a day's work to change one, as it should be. They are designed to be right the first time. They were never designed to be taken apart.

I'm disgusted. But all that said, the most common cause is a failing battery because:
1: As a battery fails the reference voltage regulator tries to adjust by turning up the gain. As battery voltage and current capacity decline further, the gain and current demand increases. The battery and regulator inverter go into a death spiral until the battery officially dies.
2: The linearity is not going to change from the factory laser trimmed value.
3: Because of the precision regulator that locks the supply voltage, the "BAT" indicator on the LCD will never come on until the display starts to dim.

Some of this can be alleviated if people, FOR ONCE by actually use the lithium battery I recommended ten years+ ago, and get 250 Hours life from it. When I have taken them in here as favors to people I have never once seen one with a lithium battery.
Now, go put Deisel fuel into your car. I don't understand the problem, because people have no problem using the correct lithium batteries in their cheap cameras.

I have been out of this business for eleven years, and been wearing Graves problems like an albatross ever since. I quit.

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 Post subject: Re: Mark 5XL repair
PostPosted: Wed Sep 20, 2017 11:35 am 
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The technical and delivery issues with the Mark5XL handpiece are disturbing. The original poster brings up a valid problem that effects some of these handpiece potentiometers and the little known need of 9V lithium ion batteries for power which must be made explicit with labeling and in the manual (if one exists). 9v lithium ion batteries do not have the wide availability that AAA and AA cell batteries do in lithium ion, so a manual should include a list of retail sources. I could find only one local outlet for 9V LI in the Clearwater/St. Petersburg, FL area.

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 Post subject: Re: Mark 5XL repair
PostPosted: Wed Sep 20, 2017 11:54 am 
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This is from a draft of the manual which seems never to have been completed or published:

XS FACETING HEAD NOTES:
The XS-x uses a 9 Volt battery. This eliminates cords, and all the troubles people have with brownouts, or line voltages in other countries. The long-life lithium-type premium 9 Volt battery is preferred, and will give over 250 Hours of use. A standard alkaline battery works well, and is economical, but if you do a lot of faceting, it would be best to keep a spare around.
Some users prefer rechargeable batteries.
The unit uses a precision DC-DC converter/regulator to downconvert the 9 volts to 5 Volts used in the electronics. It is a “smart” inverter, and even if the battery voltage drops to around 3V, will continue to provide the electronics with 5 Volts..but at this operation, the LO BAT indicator will appear soon on the LCD display, and accuracy will suffer. Imagine a marathon runner who is starving..Now ask him to do calculus! The "Lo BAT" warning does not appear until far too late. Stability suffers first. The precision inverter clamps the reference voltage. When the battery starts to get low, the inverter starts cranking up its gain. As the battery fades more, it goes into a death spiral, as it is drained still faster to maintain the critical voltage. When the battery is well depleted and nearly dead, the inverter gives up trying to save it.
The people who designed the display expected it to run directly off a battery, so used the normal discharge curves. Those calculations go out the window when a "Smart regulator" is involved.
When replacing batteries, it is good practice to turn off the Power Switch! (“Down position”) The (+) terminal of the battery goes toward the front, or quill end of the unit. In this way, if you momentarily fumble and insert the battery in the wrong orientation, no harm will occur. In the correct orientation, the battery will “Click” into its holder. Remembering to turn off the switch when you are not cutting will greatly extend the battery life. My first battery lasted about a month, cutting about a dozen stones. My second (Cheap Alkaline) battery was left on for several days, and there was not a lot left after a couple of stones. The published warmup time for the electronics to stabilize is only 3 minutes!

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 Post subject: Re: Mark 5XL repair
PostPosted: Wed Sep 20, 2017 4:25 pm 
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Location: Pine City, NY and Dothan, AL
I have found 9v lithium batteries at Wal-Mart in 3 different small cities (NY, AL, AZ). I would expect most Wal-Marts to stock them. Look in the photo department.


And there's always Amazon.


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 Post subject: Re: Mark 5XL repair
PostPosted: Wed Sep 20, 2017 4:47 pm 
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I got mine at CVS. They are a lot more common now than they used to be. Yes, Amazon, of course.

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 Post subject: Re: Mark 5XL repair
PostPosted: Wed Sep 20, 2017 8:50 pm 
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John I'm using a 9v in my Polymetric because I have unsolvable voltage issues with it in foreign countries. Do you think I would also benefit from lithium 9v's instead of the 2 rechargeables that I cycle through. I find the digital meter is only trustworthy when the battery is totally full so I exchange batteries every 2 days or so of heavy faceting.

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 Post subject: Re: Mark 5XL repair
PostPosted: Thu Sep 21, 2017 7:07 am 
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Probably. I switched to lihiums here for all my geiger counters and other equipment that usually sits idle. Rather than slowly dying like alkalines, the run until suddenly they are empty. I think the PM uses an LED display and thye are battery hogs. This is why the LCD display was chosen fr the :XS4 ("5XL") They LED are TTL, the LCDs are CMOS and run on less then 1;/10 the current.

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 Post subject: Re: Mark 5XL repair
PostPosted: Fri Sep 22, 2017 1:34 pm 
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Location: Tulsa Ok. area
Just bought a lithium for my 5XL but it wouldn't fit because it had all square sides. The old alkaline has rounded edges and just fits. Is lithium ion battery the same as lithium battery?

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 Post subject: Re: Mark 5XL repair
PostPosted: Fri Sep 22, 2017 1:43 pm 
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I have always seen them fit but very snugly, as in "Shoehorn".
Snap on the connector first and make sure no wires are bunched up, etc.

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 Post subject: Re: Mark 5XL repair
PostPosted: Sun Sep 24, 2017 2:43 pm 
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Well, looked for a round edge lithium and was told only square ones so will try again. Wife came to the shop and asked where the battery was so about two minuets later she said is this ok.

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 Post subject: Re: Mark 5XL repair
PostPosted: Sun Sep 24, 2017 3:27 pm 
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The only 9v lithiums I've seen have square corners. It's a tight fit, but they go in.


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 Post subject: Re: Mark 5XL repair
PostPosted: Fri Dec 01, 2017 3:01 am 
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As a person who had this exact same problem years ago and came here just as confused about it I have to say, thanks Gearloose for everything you've done to make this community a better place!

Your work is much appreciated!


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