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Gemini I, Unplugged Motor wire while running

 

Folks -Running an old Gemini I, SkyFi 3 and SkySafari Pro.

I somehow accidentally unplugged the DEC motor wire. ?I heard a pop, but plugged it back in. ?The DEC and RA motors still seem to run fine.

?

However, now the SkySafari display is buggered up. ?When I select a slew (DEC or RA) from the hand controller or within SkySafari, the position circle drops to the bottom of the display, then mimics the slew but in the wrong celestial position. ?When the slew button is released, the circle pops back to the correct current celestial position.

?

Any ideas on what I may have shorted out? ?Something in the Gemini control box, one of the motors, or possibly a cable?

?

I will continue to search the Gemini users group, but no answers yet.
 

On Mon, Jun 20, 2022 at 09:19 AM, <wbick51@...> wrote:

Folks -Running an old Gemini I, SkyFi 3 and SkySafari Pro.

I somehow accidentally unplugged the DEC motor wire. ?I heard a pop, but plugged it back in. ?The DEC and RA motors still seem to run fine.

?

However, now the SkySafari display is buggered up. ?When I select a slew (DEC or RA) from the hand controller or within SkySafari, the position circle drops to the bottom of the display, then mimics the slew but in the wrong celestial position. ?When the slew button is released, the circle pops back to the correct current celestial position.

?

Any ideas on what I may have shorted out? ?Something in the Gemini control box, one of the motors, or possibly a cable?

?

I will continue to search the Gemini users group, but no answers yet.

You may just need to reset Gemini and build a new pointing model from scratch. The position jumping at the start of a slew is fairly normal, as Gemini doesn't apply a pointing model during a slew, so the coordinates may jump temporarily. If the motors slew fine and the coordinates are correct after the slew, I think everything's still OK. If you suspect the motor having problems, try swapping DEC and RA motors to see if the problem moves to the other axis. If it doesn't -- it's not the motor.
 

A pop is from a spark, of course.? Your motor is running off 12-18V DC and might have had a high DC current say 0.5 amps.? The motor coils are an inductor.? ?When you unplug a powered inductor, the magnetic fueld collapses and creates a high voltage "back EMF".? Just like the old coil in a car powering the spark plug off its DC 12V battery.

So what could the high voltage spark do?? Lots of things.? It could have modified your SRAM code (which is backed up by the internal 3V battery).? Or worse.?

So I think you should first pull off your front Gemini-1 cover, and look for anything burnt, or damaged of the chips inside.? Pull out then put back the 3V battery.? That will fully reset the SRAM data from.the Eprom.??

Then while the cover is still off, put on the 12-18V DC power and boot up the Gemini again.? The handset will show "CMOS Reset" and will default to Losmandy lo action in LA area.??

Now set the UTC clock date and time.? (Code format is YYYY.MM.DD? ).? You can reset the lattitude and longitude too (Code ).? Then power off the G-1 and reboot so it will use the updated info.??

Then.. power back on.? ?While it is powered on and the top still off, gently touch the top of the black plastic chips lightly with your finger...see if any of them are very hot.? If hot, or the Gemini is still performing wacky, then suspect the hot chip or another chip is damaged.? The EPROM or SRAM or CPU can become damaged too...and the operating code data can be corrupted.? The Serial port chip is also vulnerable, so check your PC serial port connection data.? ?

If damaged, send the damaged G-1 to a repairer (me in USA, Bren Smith in Australia, or David Partridge in UK) for repair, and additional circuit bulletproofing.??

Best of luck,
Michael



On Mon, Jun 20, 2022, 7:50 AM Paul Kanevsky <yh@...> wrote:
On Mon, Jun 20, 2022 at 09:19 AM, <wbick51@...> wrote:

Folks -Running an old Gemini I, SkyFi 3 and SkySafari Pro.

I somehow accidentally unplugged the DEC motor wire.? I heard a pop, but plugged it back in.? The DEC and RA motors still seem to run fine.

?

However, now the SkySafari display is buggered up.? When I select a slew (DEC or RA) from the hand controller or within SkySafari, the position circle drops to the bottom of the display, then mimics the slew but in the wrong celestial position.? When the slew button is released, the circle pops back to the correct current celestial position.

?

Any ideas on what I may have shorted out?? Something in the Gemini control box, one of the motors, or possibly a cable?

?

I will continue to search the Gemini users group, but no answers yet.

You may just need to reset Gemini and build a new pointing model from scratch. The position jumping at the start of a slew is fairly normal, as Gemini doesn't apply a pointing model during a slew, so the coordinates may jump temporarily. If the motors slew fine and the coordinates are correct after the slew, I think everything's still OK. If you suspect the motor having problems, try swapping DEC and RA motors to see if the problem moves to the other axis. If it doesn't -- it's not the motor.

 

The help from Paul and Michael got me half way home. ?I first did a full pin-out on all the cables. ?Then did a cold reset, and the SkySafari Pro display did reset as well. ?The red position circle now tracks a RA slew. ?Unfortunately, it does not move with a DEC slew. ?The motor on the mount slews, but the tracking circle is fixed.
Cooked an encoder on the servo? ?I have a spare low power servo, and will try replacing that next. ?If that fails, I will look further into the tips suggested by Michael.
 

Pulling a motor plug out during running is undesirable but shouldn't cause damage.? Of course you need to plug it back in...but do this with a torch, power off to ensure the plug is aligned with the socket.? Get this wrong and it'll damage the motor or main PCB but putting motor drive onto the 5V line or %V line the motor plug in to ground...bad karma.??

Good thing is the repairers can fix this.?? But best thing is prevention, always plug the motor plugs in with plenty of light as the "key" for the socket/plug is not positive at best to locate.

After your even, you will need to redo a cold start and probably dump any pointing model and start again.?? Also Most parts are still available, although gamber replace you battery every year...maybe a little longer with CR2354 batteries and almost 2 years with the CR2450 batteries.?? The CR2032 can last from 3/4's of yr to 1 yr at best...depends upon a lot of things.? The more you use your system the longer the battery lasts as its reversed biased out of cct.?? I'm trying to see if I

Anyway enjoy...remember G1s are easily repaired and the same repairers (David (UK), Michael (USA) and I (the antipodes, Australia) ) can do G2s.?? I have a soft spot in my heart for the G1....it was ahead of its time and is still functioning well after ...well almost 20 years plus for some!? Most parts are still available.? .

Suffice to say....enjoy!

cheers
--
Brendan

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