Problem with Nexus DSC Pro

[Philip Manela]

Hi TACos,

My Nexus DSC Pro is no longer able to communicate with the Altitude Encoder on my DOB.

When running the built-in Encoder Test utility, The AZ encoder works fine when I rotate the scope around the pivot bolt on the ground board, but the ALT is stuck at +90.00 degrees, no matter who much I slew the scope up or down in altitude.

The head unit of the DSC Pro connects to the ALT and AZ encoders using a “Y” cable with an 8-pin RJ45 connector at the head end, and a pair of 4-pin RJ11 connects that plug into the two encoders.

To try to narrow down the source of the problem, I swapped the 2 RJ11 connections where they plug into the encoders.  

At the head unit I still see activity on the AZ side of the display, though it is now responding to changes in Altitude, and I continue to see no activity on the ALT side of the display.

This tells me that both of the magnetic encoders are able to send signals to the head unit, but for some reason one side of the cable doesn’t make to the ALT side of the display.

Next I swapped in a new cable (it came with the kit when I bought it, but was way longer than I needed so I ordered a shorter one and the original long one has been sitting on a shelf since 2022.

Same behavior.  Still no action on the ALT side of the display when running the encoder test.

This tells me the encoders are OK, the cable is OK, and either the RJ45 receptacle inside the head unit is bad, or there is a problem further inside the head unit.  Probably a hardware problem, though I can imagine corrupted firmware might also be at fault.  I confirmed that the RJ45 receptacle is clean, no debris inside.   Haven’t tried opening the case yet to look for assembly/soldering defects, though that might be the next step.

Wondering if anyone else has had a similar issue, and if so, how they resolved it.

— Philip

[Ted Hauter]

I'd spray electronics cleaner on the contacts with a paper towel covering everything else until the area drips out whatever might be in there.

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[Ted Hauter]

Meaning the piece is facing down and spraying upwards.

[Philip Manela]

I wiped down the contacts with deoxit.  They look pristine.   No improvement. 

Sent from my iPhone

On Jan 13, 2026, at 6:51 AM, Ted Hauter <thgo...@gmail.com> wrote:



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[Charlie Wicks]

Send an email to Serge at Astro Devices. He usually gets back to you pretty quickly and will call you and help you figure out possible problems/solutions.

Charlie

Sent from my iPad

On Jan 13, 2026, at 8:08 AM, Philip Manela <philip...@gmail.com> wrote:

I wiped down the contacts with deoxit.  They look pristine.   No improvement. 

To view this discussion visit https://groups.google.com/d/msgid/sf-bay-tac/632CF6C1-E9F5-41F4-84EA-80A4218EBB2A%40gmail.com.

[mtoma...@outlook.com]

Philip,

It just so happens that I have an unused main circuit board for a Nexus DSC Pro that I acquired about six months ago.  It does not work correctly, which is why I replaced it a few weeks ago.  

This board does not work correctly because I applied more than the maximum voltage to it to recharge its battery, and ended up damaging it.  An expensive boo-boo.  But I recall that the "Test" function worked just fine, and I could see the altitude and azimuth values change as I manually moved the telescope in both axes.

This board lacks the GPS module.  (I transferred it to my replacement main circuit board.)  And you cannot charge the internal battery with it.  But, again, the "Test" function works.

Let me know if you would like to borrow this board to continue your trouble-shooting.  I can mail it to you or you can come down to the Monterey Peninsula area and pick it up.  Or, meet me atop Fremont Peak the next time I am there.  (That's my new preferred local stargazing site, now that Pinnacles west has kicked us out.)  If we are together somewhere with our telescopes, you could even borrow my working DSC Pro device for a few minutes to test it on your telescope.

I have been dealing with Serge Antonov of Astro-Devices pretty frequently for the last six months.  I am in awe of how much of his time he has given me.  He nearly always answers my unscheduled FaceTime calls.  But he has never responded to any of my emails or texts.  So I end up sending a long message via email AND text, and then call him about it within twenty-four hours.  This ritual has been working very well for me.  If you speak with him, tell him that I am a big fan.

Incidentally, my Nexus DSC Pro is part of Asto-Devices' relatively new "StarDrive" go-to system for Dobs.  (It does what "ServoCAT" and "Argo Navis" used to do.)  What an amazing system.  No cables.  Altazimuth axis is driven by a rubber wheel pressing against the perimeter of the round ground board.  Altitude is driven by belts that drive rubber wheels nested inside the altitude bearing groove.  (Bad descriptions, I know.)

Mark T.

[Philip Manela]

Problem solved.

I got a loaner DSC Pro from Randy and with my encoders and cable it worked like a champ.

So I opened up the case on my DSC.  First step was to remove the rubber feet that hide 4 small screws.

The screws came out easily.  Hardest part was disconnecting the battery cable.

Most of the main PCB is find pitch surface mount IC’s and discrete components.  Assembly quality looked excellent.  Very clean.

But the RJ11 and RJ45 receptacles were hand soldered, and there was quite a bit of flux between the leads.

Over time, flux between component leads can turn into shorts.

A small brush and alcohol followed by tissue paper cleaned out this gunk, and now my DSC seems to be working fine again.

Thanks to all in the TAC community who offered suggestions and assistance.

Ted Hauter was on the right track when he suggested I flood the thing with contact cleaner.

— Philip

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[Ted Hauter]

👍

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[Jeff Crilly]

>
> On Jan 13, 2026, at 5:31 PM, Philip Manela <philip...@gmail.com> wrote:
>
> A small brush and alcohol followed by tissue paper cleaned out this gunk, and now my DSC seems to be working fine again.

That’s quite interesting. I was expecting you would need to re-solder those connectors.

Nice how this turned out.