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NexStar 11GPS Serial Board Firmware

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#1 kg74

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Posted 14 March 2021 - 06:05 PM

As I troubleshoot my dead 11GPS that suffered a power spike I am at the point of examining the Serial Board.  I purchased a new HC and it gives me the 16 and 17 errors.  It does not communicate with the MB as I get ???? listed.  I have replaced the PIC16 chips on the MB as well as some other parts.  I have used the Pickit3 to program the Pic16s with no change (I have ordered a new TL866 programmer and will follow the write ups and try again to further eliminate the MB firmware as the issue).  Nor can I access the MB with MCupdater as the scope is not found.  All the other components on the MB test correctly.

 

I have tested the components on the Serial Board (NXW493) and they test fine with my VOM.  The one I am unsure of is the PIC12F629.  I am still trying to figure out how to use my oscilloscope.

 

As the Serial Board acts as a switch board and it has firmware on it, I wonder if the Serial Board is the source of the problem, specifically the PIC12F629.  Anyone have any insights here? 



#2 Michael_Swanson

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Posted 14 March 2021 - 08:32 PM

It is certainly possible for a bad serial (main) board to cause no response errors.

 

Since you have significant electronics skills, I will propose the following.

 

It is likely possible to completely eliminate the serial board as long as you will be using a version 4 or NexStar+ hand control (this eliminates the use of the alt switch and compass - as I recall without looking at the schematics, the alt switch runs through the serial board, though maybe it was the compass or both). 

 

Essentially, you would want to wire the MC board and GPS module to a simple set of RJ-12 jacks wired in parallel and then plug the hand control into one of those jacks.  Of course you also need to get the 12 volts to the RJ-12 jacks to power the MC, GPS and HC.  Something like this could be used:

https://www.amazon.c...uct/B017B69D3U/

 

You would need to be very, very careful to get all the connections to the correct pins or you will damage the MC, GPS and HC.

 

Proceed at your own risk...

 

Best regards,
Mike Swanson
https://www.NexStarSite.com



#3 mlord

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Posted 14 March 2021 - 08:55 PM

That's a good idea.  If it doesn't work at first, you could also then short the RX/TX pins together, as is done in modern mounts (6se,8se,Evolution,etc..).  RX is at pin2, TX is on pin4 of the RJ connector.  The pin numbering on the Electronics-Salon breakout board linked by Michael matches the numbering I just used.

 

Maybe just leave the GPS out of this completely until the HC and MC are happy with each other.

 

Cheers


Edited by mlord, 14 March 2021 - 08:56 PM.


#4 kg74

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Posted 14 March 2021 - 10:21 PM

Michael and mlord - Thanks for the ideas and I will place them on the back burner.

 

I soldered wires to the PIC12F629 and rigged up the Pickit3 and pulled the hex file off said chip.  Unlike the PIC16 chips on the MB which would not even read, the PIC12 was able to be read and produced what appears to be a valid hex file.  (This is way over my head)  So I think I can eliminate my corrupt firmware/destroyed PIC12 theory for now.

 

I will refocus on the MB and try to get the PIC16 chips programmed correctly, assuming this is the issue when the new programmer arrives.

 

Unfortunately my laptop that runs the PicKit3 decided it wanted an update so I cannot post the hex file until that process is completed.  Will update.



#5 kg74

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Posted 31 March 2021 - 11:55 PM

Update.  After replacing all of the IC chips on the Motor Board except for the LS7166-S chips and confirming everything else tested correctly I could still not get the Motor Control board to be seen.  So I threw up my hands and ordered a new Motor Board.  Upon receipt I pulled the firmware off the new board and programmed the hex file to the original board.  My thinking was that if the Serial Board was bad it could damage the new board so start with the repaired board.  No luck. 

 

On the same day I received a package from GEO with a dead Serial Board and Motor Board.  As the PIC controller was operational and set up I flashed the Motor Board.  This new used GEO Motor Control board did not work.  I focused next on the Serial Board GEO sent and made a few clean up solder moves.  I plugged this Serial Board in, with the original Motor Board and I had life.

 

So, the original Motor Board was correctly repaired and the issue I was having was in fact the Serial Board.  As I had tested and/or replaced everything on the Serial Board except two chips, the 12PIC chip (it was able to be read by the programmer), the only remaining item is the SIPEX chip.  I have ordered a new SIPEX chip and will try to see if replacing it revives the Serial Board.

 

I will update, but for now those that may have a communication failure and everything seems to test okay - that SIPEX chip may be the issue.


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#6 kg74

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Posted 06 April 2021 - 10:14 PM

Update - the replacement SIPEX did not work.

 

That leaves me the Pic 12F629, which I can read with my programmer. 

 

I have read some internet articles about the "oscillator" but really don't understand.  Could this be the problem and would reflashing the chip with the hex file I pulled off it wake it up?

 

I have seen some posts for other non-scope related applications where people have ditched the 629 for a 683 which apparently doesn't have the "oscillator" issue. 

 

Any thoughts - this is way out of my understanding.



#7 mlord

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Posted 07 April 2021 - 08:05 AM

You've heard of "over-clocking a PC" and the like, right?  Well, most every CPU (PICs included) have a cycle "clock" that drives their operation, ticking them through the steps of fetching code from memory and executing it etc.  An external Oscillator device provides that clock for the PIC in this case.  Some chips have a built-in oscillator, some require an external one.



#8 kg74

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Posted 07 April 2021 - 12:29 PM

Thanks mlord - reading up on the pic 12F629, used in the 11GPS, the datasheets state the chip has an internal clock operating at 4Mhz.  Looking at the other chips there appears to be buffer chips that depend on this clock to manage the flow of information.  (My low level understanding of the relationship between the components in the circuit)

 

But based on your statement that an "external Oscillator device provides that clock for the PIC in this case", then replacing the 629 for a 683 would be an option.  Now if the 4Mhz clock in the PIC 12F629 is utilized then the 683 most likely would not work.

 

I tried rewriting the 12F629 chip, the write was successful, but the operation still fails - error 16 and 17.  Recall, I can replace the entire Serial Board with a known working one, and the 11GPS scope regains full function and operation.  So something on the board is failed.  The only remaining component is the PIC 12F629, and my trouble shooting does not point to an internal failure of the PCB itself.  My testing shows continuity and no shorts based on what I see operation should be from the traces and schematics. 

 

Reading various articles I picked up some information about calibrating the internal oscillator.  See here:  http://picprojects.o...recal/recal.htm

 

I also read articles stating that the program code, firmware, has instructions embedded concerning the same.

 

My current working theory is the Pic 12F629 was damaged - specifically the 4Mhz oscillator piece.  So the chip can be read and written to, but the oscillator component is damaged.  Again, based on reading, this oscillator component is fragile and a voltage spike could cause harm.  I don't know if the linked article above, recalibration utility, is an option or relevant.  I would assume the firmware should have the code to set the correct parameters for the chip.

 

So, the big question, if I replace the Pic 12F629 and program it with the correct firmware will anything else need to be done?  Is the calibration issue a non-issue in this application?



#9 mlord

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Posted 07 April 2021 - 12:46 PM

.. based on your statement that an "external Oscillator device provides that clock for the PIC in this case..

I don't know why I said that -- seems a bit presumptuous now, so disregard that part.

 

Do you have a schematic for the circuit?



#10 mlord

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Posted 07 April 2021 - 12:48 PM

I tried rewriting the 12F629 chip, the write was successful, but the operation still fails - error 16 and 17. 

What did you rewrite to that chip?  Where did you get that data from?  If from a different chip, then yes, the internal oscillator calibration is probably now "off".  Whether or not it matters is another question though.


Edited by mlord, 07 April 2021 - 12:48 PM.


#11 kg74

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Posted 07 April 2021 - 01:40 PM

mlord - Attached is a schematic for the original serial board as posted on the link from the old Yahoo group.  At some point it was changed is my understanding.  The Pic12 is not shown.  I don't know how useful it is, above my understanding.  Curious though the original design did not contain a Pic 12F629 so your point that timing is from elsewhere does have some merit.  In addition the earlier idea you and Mike had to bypass the board would support the 4Mhz clock is not relevant. 

 

The firmware I have is from the current PIC 12F629 that is soldered to the board.  This is the original Serial Board that came with the scope that was subjected to the voltage spike.  I soldered jumpers to the various legs and or traces per the datasheet and used my Pickit3 to read the chip (also to write the same to the chip).  So the chip is both readable and writeable.

 

I could do the same for the working Serial Board, but I don't want to push my luck at this stage and end up with two bad boards.

 

My current plan is to install another PIC 12F629, which has been ordered, and try the firmware from the original chip.  I don't see how this could be changed - it is code and shouldn't have pieces disappear and/or be changed from a voltage spike.

 

The relationship of the Pic 12F629 and the oscillator portion would be good to know in the even the swap and firmware flash doesn't work.  It will help troubleshoot failed Serial Boards and the repair requirements (is a swap and firmware flash all that is necessary or does something else have to be done).  If it is just a straight swap and firmware flash then something else is the problem (potential internal short of the PCB???) or a new component which is DOA.

 

 

Attached Thumbnails

  • Serial Main Board Schematic.JPG


#12 mlord

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Posted 07 April 2021 - 04:11 PM

I don't know enough about the architecture of that mount to help you.  The schematic above appears to be for a Motor Controller board, evidenced by the L293DO motor driver chip onboard.

 

Your mount is a GPS version, so perhaps that extra PIC is simple to interface between the internal AUX bus and the GPS receiver?  In which case completely removing the chip would eliminate it as a suspect.  I don't know if you are equipped to do that or not.  And that's just a guess.  I really should read back in this thread to re-familiarize myself with things you undoubtedly already have explained.

 

Cheers



#13 kg74

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Posted 07 April 2021 - 07:28 PM

Here is an actual photo of the board.  I agree the Yahoo Group schematic is not really helpful and appears to be a completely different design.

 

U2 is a SIPEX SP232AEN (replaced), U4 is a MM74HC (replaced), and U6 is the Pic 12F629 (not replaced but read and writeable by Pickit3 Programmer).

 

Everything else on the board is pretty self explanatory.  I did pull the 12V output connector, but that should not matter.

 

At this point I will await the arrival of the Pic 12F629 replacement and see what happens.

 

Thanks to mlord's bad influence I have purchased many new soldering tools and liking the ChipQuick solder for IC removal.

Attached Thumbnails

  • Serial Board top view.jpg


#14 mlord

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Posted 07 April 2021 - 07:52 PM

Okay, I will hazard to guess that the PIC on that board is there to implement the PC-Port functionality.  It is probably not relevant to anything else.  If defective, I suppose it could interfere with the other AUX bus items there.  EDIT: it probably also implements the Auto-Guide port functionality.

 

This entire board is not needed for the mount to function for test purposes.  It just provides a place for things to plug together.

 

Which takes us back to post #2 of this very thread.  Michael's idea is very much worth attempting in some fashion.


Edited by mlord, 07 April 2021 - 08:32 PM.


#15 mlord

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Posted 07 April 2021 - 07:55 PM

The most likely thing to fail on that board is the voltage regulator at U1.  Have you measured voltages on the pins there?

 

Oh, and can you link back from here to your original thread?  I've lost track of it and wanted to re-read things there.


Edited by mlord, 07 April 2021 - 07:56 PM.


#16 mlord

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Posted 07 April 2021 - 07:57 PM

Oh, and post a photo of the other side of the board too, if you can.



#17 kg74

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Posted 07 April 2021 - 08:05 PM

mlord - this is the original thread, but you did advise me on this post regarding some smd cap values.  https://www.cloudyni.../#entry10923529

 

I did change out U1. 

 

Here is a photo of the back.  The red wire is a jumper repair added to repair the blown trace caused by the power spike. 

Attached Thumbnails

  • Serial Board Back.jpg


#18 mlord

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Posted 07 April 2021 - 08:53 PM

Okay.  The white connectors go to cabling to various other parts of the mount.  Can you list what each such white connector goes to?

 

GPS -- probably goes to a small board with another PIC, which then connects to the GPS module.

 

COMP -- Compass??  U6 appears to be used for this, whatever it is.

 

HC -- probably just straight to an RJ12 jack for the hand-controller.

 

AUX3 -- straight to another RJ12 jack.

 

AG -- AutoGuide: probably goes to another PIC somewhere.

 

MD:  Connects to the Motor Driver (motor controller) board?

 

J1 -- 12V power.



#19 mlord

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Posted 07 April 2021 - 08:57 PM

U2 and U4 implement the PC-Port RS232 serial connection, aka. "mount serial port".  Did you say that U4 is a 74HC125 chip?  Seems likely.  We use the same chip for the same purpose in the HomeBrew projects.  :)

 

U6 now seems to be for something else, whatever is on the other end of that "COMP" connector.  I still think it could be removed from the board, and everything else should be fine without it for testing purposes.



#20 kg74

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Posted 07 April 2021 - 09:13 PM

J10 goes to GPS. 

J11 I don't know, could be Compass as you say.  It doesn't go to the Motor board though.  The schematics for the scope have a page for compass and gps.

J3 goes to the hand controller which is routed through the mount leg. 

J4 is unused.

J5 goes to the motor board.

J2 goes to the motor board.

J1 is power in.

 

Yes U4 is a 74HC125 chip.

 

As I have to pull the chip anyways I will try pulling the Pic and see what happens. 

 

Thanks again for the help.



#21 kg74

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Posted 07 April 2021 - 10:44 PM

I removed U6, the Pic 12F629, same results.  Errors 16 and 17. 

 

So now I wait for the replacement, reflash firmware and see what happens. 

 

After that I suppose the next step is get my meter out and check and note every component on the good board and do the same for the bad board.  Maybe there is an internal damage to the PCB which is grounding out something or a replaced component was DOA.

 

I will update.



#22 12Bass

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Posted 08 April 2021 - 01:55 AM

Certainly helps to have a known-good board for comparison and troubleshooting.  Curious to know what you'll find when the new PIC is installed.



#23 mlord

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Posted 08 April 2021 - 08:20 AM

I don't expect changing that PIC to make any difference, but since you've got the part coming, might as well use it.  From what I can see on the front/back photos, that PIC is probably just interfacing the compass "North detection" to the AUX bus.

 

16/17 mean that the connection from the HC to the motor controller board is bad, or the motor controller board itself is bad.  So again, post #2 in this very thread discusses how to diagnose that further.

 

Cheers



#24 mlord

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Posted 08 April 2021 - 08:26 AM

I think you are doing an amazing job here though, even if my posts don't always remember to point that out!  I offer encouragement to anyone curious enough to learn to fix their stuff!  Full Marks!

 

So, yeah, do run around with the Ohm-meter and check all of the resistors and diodes on that board.  And also check the connectivity between each of the six pins for the HC connection, and the six pins for the MC connection.  I expect them all to be hardwired together (zero resistance).



#25 kg74

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Posted 08 April 2021 - 02:56 PM

It is the Serial Board causing the error, as replacing it with a working Board and leaving all other boards the same results in a working scope.

 

I will keep working at it.  I am not one to stop until it is fixed.

 

I will keep the thread updated.

 

Thanks again


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