Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

Astro-Geek

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

Recommended Posts

In the continuing saga of my blown motor control board I've been inspecting it very closely in the feint hope of finding that the faulty compnents might be replaceable ones, (rather than any of the chips).

It looks as though a replacement board will be unobtainable for several months, (admittedly a very small thing to be concerned about during the current situation, but it keeps me occupied...)

It's the Alt motor board from my Skywatcher 300P flextube goto Dobsonian.  That's the main one, that the hand controller and 12v supply are plugged into, with a lead going on to the similar AZ board, in the base of the Dob.

I've attached high res photos of the front and back, which show there's no burnt, cracked, or bulging components, hence my hope that it may be fixable.  (I have a temp controlled soldering iron etc. and have built many projects successfully).

It was working perfectly before I caused the fault, by (stupidly) plugging the rj45 plug of an EQMOD cable adapter into the rj45 socket on the mainboard that should have held the lead to the az controller box.  There was a very feint "crack" noise from the mainboard, and now the controller still powers up, but reports that "neither axis can be seen".  So it's getting power from the faulty mainboard ok.

I'd read somewhere that the electrolytic capacitors are frequently the things that blow, but they (2 of them) look fine, and they test ok on the board when you apply a multimeter across them (low res, then infinity).

Any prcatical ideas or suggestions most gratefully accepted...... 🤓

 

 

mc004 back.jpg

mc004 front.jpg

Share this post


Link to post
Share on other sites

quick one, check D1 & U1, for the right volts....

  • Like 1

Share this post


Link to post
Share on other sites

Wow, that was quick Julian...  👍

Volt readings on attached image,  I think they're all ok ?

I can go into more detail with the error testing, as long as I can explain myself clearly !

When I tried it after the "crack", and unplugging the eqmod cable and replugging the rj45 to the remote  az controller board, the synscan controller could still "see" and operate that remote az motor, but the alt motor was unresponsive.

So, as this Alt board and the Az board in the base seem to be identical PC boards, with the same chips and components, the only differnce between them is that other "remote" board does not have the hand controller RJ11 socket, the coax power socket, or the on/off switch socket.

So when I blew this one, the Az board was safely unplugged (🤓), so my error blew the Alt circuitry in this board but still allows the hand controller to communicate through the RJ45 socket to the AZ board.

Then, I updated the firmware in the Synscan controller, from v.03.08 to the latest version, and now there must be more initial testing when the controller is switched on, because it can't see or control the Alt or the Az axis.

answer1 volts.jpg

Share this post


Link to post
Share on other sites

If you are careful, you 'could' fit the missing components to the other board, and swap their roles.....

If all worked ok, it would then give you a 'working' model, you could compare to the broken, to at least narrow down your search, but if its the big U5 then you're out of luck as Synta get them modded from a standard part.

  • Like 1

Share this post


Link to post
Share on other sites

mmmm.......

I'd be a bit nervous about that. 🥴

It would seem a bit like altering a reserve parachute with bits from the main parachute while freefalling from the sky.........   🤓

Even when you can get these boards, they're over £100 each....

Share this post


Link to post
Share on other sites
Posted (edited)
3 hours ago, Dr_Ju_ju said:

If you are careful, you 'could' fit the missing components to the other board, and swap their roles.....

If all worked ok, it would then give you a 'working' model, you could compare to the broken, to at least narrow down your search, but if its the big U5 then you're out of luck as Synta get them modded from a standard part.

....you talked me into it Julian....  🤓

When I compared the two, the only apparent difference is just three "large" passive components, an RJ11 socket, a coax power socket, and double pole socket for the power switch.

I set to work carefully with my solder sucker and temp controlled iron and shifted them across.

I'll test it tomorrow and let you know the result....

I did another interesting test earlier this evening,  I managed to find a copy of SynscanAZ 3.08 firmware and installed it on the handset, setting it back to where it was before I flashed it with the latest universal AZ/EQ firmware from the skywatcher site.

That version appears to have less stringent power-up tests, because it didn't bleep with "no connection to mount".

With the master (Alt) and secondary (Az) boards connected in their normal places, I was able to slew the Az axis, but not the Alt Axis.

I then switched the boards over, so that the master board was connected to the Az and the secondary board was connected to the Alt, and then I was able to slew the Alt, but not the AZ.

That makes me fairly confident that there's nothing wrong with the motors or the sensors, or the secondary board.

 

Edited by Astro-Geek

Share this post


Link to post
Share on other sites

A couple of comments if I may.

A 'faint crack' is usually sign of the plastic package of a component breaking due to internal heating.
That component can be almost type, but tends to be the physically larger stuff.
If you have a half decent microscope of some sort, have a really good look at all the large components. Especially the line where the top/bottom parts of IC packages have joined.

I do not advise swapping components between boards. They have already been heat cycled in manufacture. You plan to heat cycle them for removal - which is very dtressful. Then heat cycle them again for resoldering.
At the end of all this, the reliability of the part is suspect so may cause confusion.
A far better approach is to buy a new component. Most are cheap as chips. OK I'll get my coat😏.

Looking at the small amount of ESD/surge protection on the incoming supply, I can see a good argument for taking my dob goto apart to improve on this.

HTH, David.

 

  • Like 1

Share this post


Link to post
Share on other sites

Thanks for the thoughts and advice David.

I certainly wouldn't have tried desoldering any active components from the board, but as there were only three additional parts on the broken board and they were all low priced connectors (an RJ11 pcb jack, a coax power pcb jack, and a double pole connector), I did swap them over last night.

I've just been out to the Pod and tried them out with interesting results...

So to recap, the goto Dob has two almost identical motor controller boards, (with postition sensors).

The Alt axis one, which I will refer to as the "Master", was in the box on the Alt axis, and had the connections for the RJ11 synscan handset, the coax power socket, and the RJ45 lead down to the az controller box on the Az axis in the base.

The Az axis one, which I will refer to as the Slave, was in the box on the Az axis, and only had one RJ45 connection, which was the lead from the Master controller.

So, before I made any changes, I tested the controls with Synscan v3.08 firmware and the AZ axis was working perfectly, slewing, changing rates etc..  But the Alt axis was dead, no response. 

So when I blew the board by plugging an EQMOD adapter into the RJ45 socket on the Master,  the Slave was safe because it was disconnected, and I must have blown the Alt circuitry on the Master board.  When the Slave was plugged back in, that worked ok, so that part of the circuitry on the Master board that lead to the slave and the handset power was ok.

I also tried switching the Master and Slave boards over, so that they were connected to the opposite but identical Alt and Az motor units.  As expected, the Alt motor then worked correctly, and the Az was dead.

So, as the boards appear to be identical apart from the three sockets, I switched those over, making my Master the Slave and vice versa.

I now have exactly the same results with the tests, so it would appear that the circuitry on the original master board that controlled the motor directly connected to it is what has blown.

So the 64,000 dollar question now is, if I bought a replacement "slave" ( Az ) MC004 board, would that fix the problem ?  ( I think one of those may be "in stock" somewhere 🙂).

I think it would depend on whether the big U5 chip is programmed differently between the Alt and Az (master and slave) MC004 boards.

Gut reaction tells me possibly not, they both seem to just treat the directly connected motor as the Alt, and the remotely connected one via the Rj45 lead as the Az....

Sorry about this long rambling post, but I really apprecate the ideas and suggestions that I'm getting on here....

 

 

 

 

Share this post


Link to post
Share on other sites
52 minutes ago, Carbon Brush said:

.....If you have a half decent microscope of some sort, have a really good look at all the large components. Especially the line where the top/bottom parts of IC packages have joined.......

I'll do that David, one of my toys is a cheapo binocular microscope, which will give me a 20x magnification on it.

Share this post


Link to post
Share on other sites

Even if it was flashed differently, and if you're confident in doing it, you could always flash it to the same version as the other one, or even flash both to the latest & greatest....

  • Like 1

Share this post


Link to post
Share on other sites

Alas Julian, chip flashing is beyond my abilities.....   (other than the nice turnkey progs for popluar firmware updates.)  🤓

Share this post


Link to post
Share on other sites

Its still the same, just using different tools....

  • Like 1

Share this post


Link to post
Share on other sites

...but wouldn't the chip have to be removed from the board ?  😱

Share this post


Link to post
Share on other sites

I'm no electronics expert, but have built my own projects, and fixed my own HEQ5 main board, which was indeed the replacement of two electrolytic caps.  Looking at the images the PCB us very modular, with what looks like lots of surface mount links designated as L1, L20 etc as most other components will have values printed on them.  It may be worth checking continuity through these components.

The other issue, is that if you heard something crack and fizzle then that would suggest something major has happened to a component.  Just because you can see it doesn't mean it hasn't happened.  Chances are it may have popped under the component which is why its not visible.

  • Like 2

Share this post


Link to post
Share on other sites

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

  • Like 1

Share this post


Link to post
Share on other sites
Posted (edited)

I assume the EQMOD cable you plugged in was connected to your PC USB port at the other end. If it wasn't I couldn't see it causing any harm. The USB Eqmod cable only uses pins 4, 5, and 6 on the RJ45, with pin 4 being Gnd (may also be pin 1 instead of, or as well) and pins 5 being RXD and pin 6 TXD, both 5V TTL levels.

Assuming I've got my mental gyrations correct on orientating the RJ45 on your board

Pin 4 (Gnd) is already connected to pin 1 on your PCB which is fine, and then appears to connect to L4

Pin 5 (RXD) being an input (high impedence) shouldn't upset your board though it is connected to L5

Pin 6 ( TXD) being an output (TXD) doesn't appear to be connected to anything on your board.

It's worth checking continuity on L4 in particular, and the other inductors going to the RJ45 section of your PCB for good measure, to confirm they still measure short circuit.

As malc-c suggests it's quick to check the continuity of all the L components on the board. The 'crack' noise you heard could easily be the ferrite core of one of these inductors cracking as the thin wire in the inductor got hot and melted due to excessive current. L4 being shorted to ground by your Eqmod cable is a prime candidate.

Edited by symmetal
  • Like 2

Share this post


Link to post
Share on other sites

Looks like pin 7 on the motherboard is connected to the microcontroller via L7 and pins 6 and 8 to ground. Pins 7 and 8 on the EQMOD cable supply power.

Share this post


Link to post
Share on other sites
On 07/04/2020 at 16:11, Astro-Geek said:

I caused the fault, by (stupidly) plugging the rj45 plug of an EQMOD cable adapter into the rj45 socket on the mainboard that should have held the lead to the az controller box.

 

1 hour ago, symmetal said:

I assume the EQMOD cable you plugged in was connected to your PC USB port at the other end. If it wasn't I couldn't see it causing any harm. The USB Eqmod cable only uses pins 4, 5, and 6 on the RJ45, with pin 4 being Gnd (may also be pin 1 instead of, or as well) and pins 5 being RXD and pin 6 TXD, both 5V TTL levels.

 

I'm not very familiar with these new mounts and the boards contained in them.  Can the OP confirm what the AZ control box is ?  - do you mean the hand controller or are there multiple boards in the mount ?  Whilst the EQMod cable does indeed have 5v logic, if the port it was plugged into had higher voltage levels then who knows what damage that may have done to sensitive components, especially if they are running at 3.3v logic.

Share this post


Link to post
Share on other sites
2 hours ago, symmetal said:

I assume the EQMOD cable you plugged in was connected to your PC USB port at the other end. If it wasn't I couldn't see it causing any harm. The USB Eqmod cable only uses pins 4, 5, and 6 on the RJ45, with pin 4 being Gnd (may also be pin 1 instead of, or as well) and pins 5 being RXD and pin 6 TXD, both 5V TTL levels.

Assuming I've got my mental gyrations correct on orientating the RJ45 on your board

Pin 4 (Gnd) is already connected to pin 1 on your PCB which is fine, and then appears to connect to L4

Pin 5 (RXD) being an input (high impedence) shouldn't upset your board though it is connected to L5

Pin 6 ( TXD) being an output (TXD) doesn't appear to be connected to anything on your board.

It's worth checking continuity on L4 in particular, and the other inductors going to the RJ45 section of your PCB for good measure, to confirm they still measure short circuit.

As malc-c suggests it's quick to check the continuity of all the L components on the board. The 'crack' noise you heard could easily be the ferrite core of one of these inductors cracking as the thin wire in the inductor got hot and melted due to excessive current. L4 being shorted to ground by your Eqmod cable is a prime candidate.

I'm afraid I can't remember whether it was connected at the PC serial plug end, but it probably was.

Thanks for the testing suggestions, I'll start on them right away.

Share this post


Link to post
Share on other sites
24 minutes ago, malc-c said:

I'm not very familiar with these new mounts and the boards contained in them.  Can the OP confirm what the AZ control box is ?  - do you mean the hand controller or are there multiple boards in the mount ?  Whilst the EQMod cable does indeed have 5v logic, if the port it was plugged into had higher voltage levels then who knows what damage that may have done to sensitive components, especially if they are running at 3.3v logic.

Sorry for the confusion, all of my refernces to controller boards are to the ones in the mount, not the Synscan hand controller.

The configuration of the Skywatcher goto Dobsonions is two seperate boxes, each with a motor "controller" PCB, the "master" one being on the Alt axis pivot, and the "slave" being in the base, over the az axis.  Each of them have a sensor too, so that the Dob can also be pushed manually, without losing sync.

The power supply section of the board seems to supply 12v and 5v, so hopefully there's no 3.3v in there.  (but that is a best guess on my part).

Share this post


Link to post
Share on other sites
2 hours ago, Dr_Ju_ju said:

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

Excuse my ignorance on this, but if the motor boards can be flash programmed in-situ, wouldn't they  need some sort of Skywatcher Engineer only flashing programme ?

Share this post


Link to post
Share on other sites

Thanks for all these replies, much appreciated....  🍺

Share this post


Link to post
Share on other sites

As long as you have the firmware downloaded from Skywatcher, (they don't hide it very well....) and their flash programming utility, as long as you have some patience, then its easy.....  I've also used Bossa flash utility, which can give you more control over the process.

  • Like 1

Share this post


Link to post
Share on other sites

I've drawn another blank I'm afraid.......

I checked all of the inductors on the board, and I get less than 1 ohm on my meter with all of them.....

I also used my binocular microscope on it at 20x, and couldn't find any damage visible.  (at that magnification the solder blobs look like Christmas Puds !)

Share this post


Link to post
Share on other sites
2 hours ago, Astro-Geek said:

I've drawn another blank I'm afraid.......

I checked all of the inductors on the board, and I get less than 1 ohm on my meter with all of them.....

I also used my binocular microscope on it at 20x, and couldn't find any damage visible.  (at that magnification the solder blobs look like Christmas Puds !)

That's a pity. Running out of ideas I'm afraid. :frown:

Alan

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.