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Meade AutoStar Replacement

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#26 OzAndrewJ

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Posted 25 April 2024 - 09:46 PM

Gday atechlabs

 

I'm unsure if this is what you meant by alternate mode, so please correct me if I am wrong.

Start the mount and leave it in AltAz mode.

In that status,the motors wont attempt to start until you start an align

Now press and hold mode for several seconds and release.

You now get the alternate menus.

Scroll to AltAz and then use the slew keys

A dead encoder feedback loop means the mount wil go to max

and the position wont change.

If it goes to a high speed and the display changes a bit,

then there is "some" feeback going on, but its dodgy.

 

By default the handbox is in Alt-Az mode on startup. If I switch to polar mode (Setup>Telescope>Mount>Polar), the base motor spins up to full speed and continues until about 15 seconds later it stops and the handbox displays the motor fault message.

Correct. As i mentioned earlier, if it gets a command to move, but gets no feedback

the motor card ramps up the speed to try and get feedback

Setting the mount to Polar automatically starts the RA tracking

hence why you leave it in alt az mode.

 

I am not familiar with the LED but its normally a simple IR unit

with the smarts being in the receiver

Dave can probably give more info here as he has worked on them.

 

Andrew Johansen Melbourne Australia



#27 DAVIDG

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Posted 26 April 2024 - 09:07 AM

 The IR system for the encoder use a IR LED and phototransistor  both that run on 5 volts. The system needs 5 volts since that sets the reference level and it also might be causing the PIC that controls the motor to be a in Brown out condition and not starting if the voltage is low. If your voltage regulator  is not supplying 5 volts that is first thing I would fix. 

 

                - Dave  


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#28 AtechLabs

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Posted 26 April 2024 - 11:07 AM

Thank you both for the advice! I've got some 5V regulators on order, so while I wait for those I tested in Alt-Az Alternate mode. The motors seem to go to max power but the handbox coordinates don't change. After some time spinning the handbox reports a motor unit fault. The motors will still respond to the handbox 4 button controls when the message is being displayed. 


Edited by AtechLabs, 26 April 2024 - 11:09 AM.


#29 DAVIDG

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Posted 26 April 2024 - 12:16 PM

Thank you both for the advice! I've got some 5V regulators on order, so while I wait for those I tested in Alt-Az Alternate mode. The motors seem to go to max power but the handbox coordinates don't change. After some time spinning the handbox reports a motor unit fault. The motors will still respond to the handbox 4 button controls when the message is being displayed. 

 With no change in position reported on the hand box and it going to max speed that indicates the encoder is  not reading. The fact that the motor moves with the hand controller indicated that the PIC is working but it is not reading the signals from the encoder.  Here is basic schematic for the design. It uses a resistor ladder to set the brightness of the LED  which determines the response of the photo transistor. Note the transistor is biased by a 5.6K resistors to limited it's response.  You said that the IR LED is working so either the phototransistor is bad, the input from the transistor on the PIC is bad or the brightness level from the LED is out of range to have the correct response range for the PIC.  All this is based on having a voltage of +5 volts. So my guess is that will voltage being low, the whole encoder system is out of range for  voltages that the PIC is expecting. 

 

                        - Dave 

DS motor control card.JPG


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#30 AtechLabs

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Posted 27 April 2024 - 08:28 PM

The regulators arrived today and I can now calibrate motors without a Motor Unit Fault! Looks like all the problems are, as Dave suggested, due to an undervoltage issue with the controller. Many thanks to everyone for the help! I'll post another update after I get a chance to actually use the telescope! Sadly I've got overcast skies for a while. 


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#31 OzAndrewJ

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Posted 27 April 2024 - 09:37 PM

Gday atechlabs

Just for info, have you done the "pinky test" on the reg after fitting

ie is it a better unit, but still getting hot, but not enough to fail????

Just seems off the other one was partially working

so wondering if there was/ is a partial short somewhere??

 

Andrew Johansen Melbourne Australia


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#32 AtechLabs

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Posted 28 April 2024 - 09:57 AM

Hello Andrew, 

 

Yes, the regulator seems to operate at a comfortable temperature. It's attached to the board with hot glue that isn't melting, so I think it's okay!

I don't think there is a short anywhere, I suspect the original regulator was damaged from the reverse polarity incident. I saw a small pinhole in the IC and smelled the magic smoke, so I think it must have not had any reverse voltage protection. I can check the Iq of the whole board if you happen to know the ballpark current draw without the motors running.


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