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Any ideas on repairing a (slightly!) blown motor board ?


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Well I've just received a PM from the owner and he's a happy bunny... Yes it's four out of four guys Due to their personal commitments they haven't had the time to put the thing through its pace

Hello everyone, I am that happy owner  who sent this badly damaged MC-003 board to Malcolm and received it back in fully working condition   I wanted to make a video showing that everything is working

We'll it looks like we've scored another goal in extra time The first thing I did this morning was to re-flash the PICs with the same 209 hex file I originally used.  Now as the PICs were solder

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  • 3 weeks later...
On 08/04/2020 at 16:43, Dr_Ju_ju said:

Noooo no removal of components, the system is designed to be flash programmed.....

Thanks for the encouragement,  I did find the correct firmware loader and motor controller firmware on the Skywatcher website, and you were quite right, it was a straightforward turnkey operation.

MC Firmware loader v1.74 and DOB Goto Motor Controller Ver 209.mcf

I connected it to my PC via the skywatcher cable from the RJ11 on the handset to an RS232/USB adapter in the PC.

The firmware loader identified the existing motor firmware as v 2.9.98

It then went from 1%  to 100% of programming "MCU1", then after a few seconds, said that the update had failed, and to try again.

I did it three times, but with the same result.

When I then started the Synscan in the normal way, it was the same symptoms as before, it went through the startup tests, and then I could operate the left/right AZ axis successfully, but the moment I tried the up/down ALT, the motor didn't move, and the controller froze.

I'm confident that both of the motors themselves are ok, because when I fit the Alt board to the AZ motor and the AZ board to the Alt motor, then the Alt motor moves the scope up and down, and then the AZ freezes with no movement.

It's tantalsing me, the fault appears to be something quite minor (though I could be quite wrong), with no apparent problems to the power circuit, because it runs one axis, powers the handset, and even allows the firmware loader to communicate with it, up to a point.

Getting a replacment board appears to be a hopeless task for several months under the current circumstances, I've tried everywhere.

Edited by Astro-Geek
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I personally don't think this is something minor

Observations:

The handset communicates with the mount.  You can move the mount in AZ.  The PC software can communicate with the mount and identifies the existing firmware. - This means the processor is working on the main  board.

The mount can be moved via the hand controller in the AZ plane - this would suggest that power is getting through to the motors and that the driver chips on that axis is fine (assuming that when powered you have resistance in the motor of the axis that has failed).

The fact that you get no movement on the ALT plane would suggest that either the motor is non-functional, or the driver chip or one of the associated support components has failed.  The fact you swapped motor connections and it functioned would thus point towards component failure for the driver board used.

Now unless you have access to scopes or other test equipment and SW were forthcoming with a schematic  (the latter I doubt), and the ability to desolder and re-solder to component level then it might be time to bite the bullet and purchase a new board.  The drawback is that OVL have closed (AFAIK) due to CV19.

I'm only familiar with the HEQ5 which has the one main board rather than a mainboard and two driver board (you mentions swapping ALT and AZ boards).  If this mount has two  such "driver" boards and you#ve swapped them and the fault follows the board then it would indeed suggest in issue with just that board.  This could be a simple capacitor or, and gut feeling, the actual chip that does the pulsing.  The only fly in the ointment is the fact that whilst the PC software can read the existing firmware, the bootloader wasn't able to update it.

 

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Thanks for the very detailed reply Malcolm.

Yes, as each of the two  identical motor  sub-assembles still function perfectly when the two (almost identical) driver boards are swapped over, I'm relieved that all indications point to just the main "ALT" MC004 motor board.

After gratefully received helpful suggestions on this thread, I've tested the voltage at various points and the resistence of inductors and the momentary "kick" of the capacitors with a multimeter.  I have  middle of the road abilities in un-soldering and re-soldering most surface mounted components on the board, (temp controlled iron, sucker etc.), but yes, the chips are certainly out of the question for me, even though it's not a multi layer sandwich pcb.

I'd happily order a new replacement board and have tried most UK and EU spares stockists, but the current extreme circumstances has resulted in understandably vague quotes of "several months", so I'd prefer to not be tied into any specific open ended delivery date order.

I did contact OVL, and they did reply two weeks ago to say that the factory advised them that "a different one was available now" and they were seeking further clarification. No further reply yet though.

I guess it's probably just a coincidence, but initially I was able to get a replacement MC004-Alt board form Teleskop Express, but when it came it was a completely different type, with a completely different model number, as explained on this thread:

It's curious though, it was exactly the same size, with the same fixing hole centres, and had the same flying lead connectors on it, but it had absolutely no components on it at all, no chips, inductors, capacitors etc..  so I can only guess that it was some sort of breakout board for testing possibly ?  (there were additional lead connectors on it, to presumably couple it up to another board).

Teleskop Express were very good though, they immediately sent a postage paid EU express return label, and have refunded me in full.

Edited by Astro-Geek
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I must admit I'm struggling here.... On the HEQ5 and EQ6 mounts there is a small interface board where the handset / power and ST4 cables can be plugged in, with a cable connection to a single motherboard.  The two steppers connect to the motherboard directly.  In your posts you give the impression that there are sub assembly boards with the motors on board rather than just the wires from the motors on each axis.  But as you have plugged each axis motor / sub assembly into the board on the good known working port and they work, then it would suggest its the chip that that drives that axis that's the cause of the problem.  Can you post up a connection diagram?  I'm presuming that the other connectors on the board are for encoders so the mount can still track and goto even after a manual intervention?

However, as mentioned, without test equipment to see what signals are like on the chips I doubt that you will ever get to the bottom of this issue.  With OVL out of action and not able to give you a lead time on spares then its a case of sit and wait until restrictions are lifted and a replacement board can be sought.

 

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You could connect a amp meter in series with the supply and see if the board sinks more current than expected. If that is the case, try to locate any heat source among the different components.

Ragnar

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I had the same issue trying to get a motor for my HEQ5, eventually found one after much searching, otherwise it was about 3 months delivery.

Did you ask https://grovers.biz/optics/spares-parts/6545-sky-watcher-motherboard-dobsonian-sky-liner-synscan.html for a lead time.

Also might be worth asking these guys https://tavcso.hu/en/productgroup/szerviz_motherboards doesn't show your particular board but doesn't cost anything to drop them an email.

 

Kev

 

 

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3 hours ago, lux eterna said:

You could connect a amp meter in series with the supply and see if the board sinks more current than expected. If that is the case, try to locate any heat source among the different components.

Ragnar

The only problem there is that unless a component glows or smokes there is no means of telling if the current draw is excessive or not as SW don't release technical data at this level. - but good suggestion otherwise.

 

 

2 hours ago, Kev M said:

I had the same issue trying to get a motor for my HEQ5, eventually found one after much searching, otherwise it was about 3 months delivery.

Did you ask https://grovers.biz/optics/spares-parts/6545-sky-watcher-motherboard-dobsonian-sky-liner-synscan.html for a lead time.

Also might be worth asking these guys https://tavcso.hu/en/productgroup/szerviz_motherboards doesn't show your particular board but doesn't cost anything to drop them an email.

 

Kev

 

 

That's surprising you had to wait so long as the steppers in the mount are standard NEMA brand and these are commonly available from loads of sources 

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7 minutes ago, malc-c said:

The only problem there is that unless a component glows or smokes there is no means of telling if the current draw is excessive or not as SW don't release technical data at this level. - but good suggestion otherwise.

 

Of course this is just a hit or miss troubleshooting procedure, but I once repaired a pcb that way just by using my hands to feel the slight heat from one faulty component. Which reminds me of another case when no heat was emitted, I increased the current to whatever was the maximum but no heat. I was going to ditch that pcb but decided to push it further so I connected it to my car battery (yes!) with long cables so nothing was jeopardized, and there was a nice flame from the faulty (tantalum) capacitor.

Ragnar

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I've done fault-finding in the past using an IR thermometer to check component temperatures - sames burning your fingers.

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Thanks for the further replies, all ideas gratefully received.....

Yes, the circuitry in the goto Dobs differs from most other goto motor boards in having two almost identical layouts, one for each axis.

This photo shows the pair, the one on the left is the AZ from the base and the one on the right is the ALT from the left side trunnion.

The Alt acts as the "master" with the coax power input, handset RJ11 (because it's an altaz mount), and the RJ45 to the RJ45 socket on the "slave" AZ board and motor.

Yes, each board has connectors on it  for the motor and encoders closest to it.

So as they're identical, there's probably redundant circuitry on the "slave" AZ board, even though it has empty solder points for the missing sockets.

connections.jpg

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Right, I have a better understanding on how the mount is configured.  Bit confuddled with each board having two motor terminals, one being three wires as most steppers use four so no idea what the 3 pin socket does.

I know it seems obvious, but have you tried a different RJ45 lead (without a diagram its hard to know if it used a cross-over cable or straight through)

Is power to the "slave" board fed through the same RJ45 lead ?

They appear to be identical boards, other than one has the power switch and socket and the handset connector removed.  I doubt that they would have different firmware on the processor (could be wrong).

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Keep them coming.....  🤓  (please)

I don't think it could be the RJ45 lead because  it is the AZ slave board that has the fully operational motor, so that is working perfectly together with the single RJ45 connection to it.

That's why it's so tantalising, the "master" Alt board is able to run the synscan hand controller and power and operate the slave AZ board, and yet it can't get any response from "its own" directly connected Alt motor connections.....

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My guess is that its a driver chips that's failed (possibly one or both of the 14 pin packages) on the master.  I'm betting that the two boards are identical with the same firmware on each, and the two processors communicate using some CAN bus or similar, which is why the slave board works and you don't get any error messages on the handset.  Can you advise what markings are on those chips.  With some flux and careful use of a soldering iron those should lift quite easily and would be the things i would replace if this was my board

mc04.jpg

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3 hours ago, malc-c said:

That's surprising you had to wait so long as the steppers in the mount are standard NEMA brand and these are commonly available from loads of sources 

The problem with the HEQ5 is that the shaft is reduced at the end from about 4mm down to 3mm to accept cog...so unfortunately not standard.... trust me I looked everywhere that I could find

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Ah, so it was more of a physical issue than electrical.  I've used NEMA motors in s few projects and thought the flats an shaft lengths were standard.  Mind you, wouldn't put it passed SW to come up with some " exclusivity" in order to sell them at infated prices

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55 minutes ago, lux eterna said:

It does not make sense with 4 + 3 pin connectors to each motor for just 4 channels used. What could be the reason to that ?

Ragnar

I thought that, and I think I've discovered something.  The motors in this mount may not be steppers.  If you look at the large image on page one you see that pins 3 and 6 go to the two outer pins of the three pin socket labeled MOTOR.  There are two capacitors between pins 3 and GND and 8 and GND.  As there is only one set of two wires this would suggest the motor suggest that the motors used are DC, and that the use of precision encoders are used to maintain tracking.  Not sure how the motors are locked off as steppers have a holding torque....

Edited by malc-c
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Reading up on the goto dobs, they use DC motors with dual encoders on both axis.  This would explain the two 4 pin headers labeled IR sens and the three pin Motor header.  It would also explain how the scope can be moved whilst tracking, something that is difficult to do with stepper motors because stepper motors get locked by the two phases.

Given this, it should be possible to use a standard DVM between GND and pin 3 and then GND and pin 8 to see if there is any voltage being sent to the three way terminal header.  If there is no voltage then this would confirm the L293DD chip has blown.  Repeating this on the good board that is known working should confirm this.  Again this is presuming that the DC motors are being controlled by pure DC and not some form of pulse width modulation, which would need some scope or logic analyzer to confirm, but from what i've researched this evening, the direction control (and speed) is via the corresponding GPIO pins going logic high or low... 

Edited by malc-c
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Sorry for the delay in replying, the sky was clear so I was having a look at the new Moon, just before the clouds rolled across it, (thank God for permanent Obsys..) 🤓

..Wow, thanks for all the detail.

Yes, the goto Dobs (Skywatcher and Orion) have "dual encoders", and the ability to push to saves a lot of time with big slews.

I'll read through your suggestions a few times then give them a try tomorrow in the Obsy (it's too big to drag indoors !)

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