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Frequency Asked Questions about Gemini

Questions
Click on questions to go to answer


1.   What does it take to add a second communication port to the Gemini Controller?

2.   Why does the Gemini Stop and wait for startup instructions if the hand controller is not present?

3.   Can the hand controller be removed with power on, and the USB or RS-232 Adapter connected?

4.   Can the 9 Pin Powered Version of the RS-232 adapter be connected to a PC?

5.   Can TheSky6 be used through the USB or RS-232 Adapter?

6.    Can more that one program be used to control the Gemini Control box, one connected to the normal RS-232 port and another connected to the Gemini USB Adapter or Gemini RS-232 adapter (Not in production anymore).

7.   Can a Blue-Tooth adapter be directly connected to the Gemini USB Adapter?

8.    Can a serial-Blue Tooth adapter be connected to the RS-232 Adapter? (NOTE: This device is no longer in production)

9.    Can the USB adapter be connected to a USB GPS Unit?

10.    What is a ground loop and how can you test for one?

11.     How do you disable the Gemini modeling, to use T-Point or ACP

12.     Is it possible to use more than one USB-serial adapter at one time on a laptop?

13.    How do you install the ASCOM Driver in TheSKY6?

14.    How do you determine the Com Port of a connected USB to Serial Adapter and change it?

15.    What is the different between the old and new autoguider ports?

16.    How do you get Windows 2000, XP, Vista & Win7 to show all the com ports that have been allocated?

17.   What are the changes between L4V1.02 and L4V1.04 EPROMS?

18.   How do you determine if the RS232 chip in the Gemini is bad?

19.   Can you run the Gemini without the motors connected safely?

20.   What will cause the Gemini to shut down the hand controller?

21.   What does the red dots on the hand controller mean during boot?

Answers

1.   What does it take to add a second communication port to the Gemini Controller?
Answer: THESE ADAPTERS ARE NO LONGER AVAILABLE!  The ASCOM Gemini .NET driver now provides a way to have 2 programs control the mount.
The Level 4 Firmware now provides a way to add a second communications port to the Gemini Controller. This is done by removing the hand controller and adding either a  USB Isolated Adapter. When you add this adapters to the hand controller port (DB15 connector on the side of the Gemini controller), you now have a USB port plus the normal RS242 port. This second communications port has all the functionally of the RS-232 port on the front of the Gemini. You can have 2 computers connected at the same time, or one computer with 2 ports connected, or a computer and GPS connected.
This adapters has been tested with Gemini Control Center (GCC) Level 4, and with the L4 and L5 versions of the ASCOM drivers. Please note that when powering up the Gemini, using this adapter, that the Gemini will stop and wait for a program to tell it which mode to boot in. SEE FAQ2 Also note that the hand controller is disconnected, so it is non-functional, when one of the adapters is connected. You can use the hand controller emulation provided in GCC to emulate the hand controller.
The question of how the Gemini works with two programs comes up a lot. If you are using ASCOM with the POTH HUB, the Gemini is already working with many programs at once. All the programs that I have tested, normally if they receive a response from the Gemini that they did not initiate, just ignore the response. The Gemini never initiates a command except in the case of it trying to get GPS data. It only does this out the normal RS232 port. however


Special WARNING to USERS of OLDER GEMINI UNITS THAT HAVE THE DISPLAYS ON THE GEMINI CONTROLLER ITSELF. Using one of the modules will cause the On-Board display to be blank and not function as long as the module is attached. This is normal. The data to the display is being modified to become RS-232 data and is not compatible with the display data format. The Gemini will work just like the newer Gemini's that has the display in the deluxe hand controller. Use a display emulation program such as GCC.

2.   Why does the Gemini Stop and wait for startup instructions if the hand controller is not present?
Answer:   The Gemini unit has to have either the hand controller or an external computer to tell it which mode to boot in. When the Gemini initializes, it looks to see if a hand controller is connected, or some other type of communications adapter is connected to the DB15 pin connector.  If it detects a hand controller, then it will go ahead and send out the display commands to the hand controller.  If a hand controller is not present, or a Second Serial Port adapter is present, then the Gemini will stop and wait for a signal into either the normal RS-232 port or the Second Serial Port, to tell it that a computer or PDA or some kind of controlling device is present.  The controlling device has to be able to tell the Gemini what mode to start up in.

3.   Can the hand controller be removed with power on, and the USB or RS-232 Adapter connected?
Answer:  THESE ADAPTERS ARE NO LONGER AVAILABLE!  The ASCOM Gemini .NET driver now provides a way to have 2 programs control the mount.
YES, the hand controller can be removed while the Gemini Control box is powered Up.  If the mount is in a tracking mode such as sidereal, then the mount would keep moving.  You can then add one of the three communications adapters listed in FAQ1. The Gemini will then detect them. You have about 1 minute to do this swap normally. It is suggested that you either stop the tracking or park the telescope first to prevent the telescope from possibility hitting the mount or going into a safety zone.

4.   Can the 9 Pin Powered Version of the RS-232 adapter be connected to a PC?
Answer:   THESE ADAPTERS ARE NO LONGER AVAILABLE!  The ASCOM Gemini .NET driver now provides a way to have 2 programs control the mount.
No, not directly.  My testing has shown that the +5VDC on pin 9 into the PC shuts down the serial port.  I tested this with both dedicated serial ports and USB - Serial Converters.  All tested ports would not work.  No damage was done to any of them, this signal just turns off the serial port.  However Astronomy Stores now can provide you with a Male/Female DB9 (Power Blocker) adapter with Pin 9 Removed, that will allow you to connect the 9 Pin Powered Version of the RS-232 adapter to a PC at low cost.

5.   Can TheSky6 be used through the USB or RS-232 Adapter?
Answer: THESE ADAPTERS ARE NO LONGER AVAILABLE!  The ASCOM Gemini .NET driver now provides a way to have 2 programs control the mount.
Yes there are 2 ways to get TheSky6 to work.  If you use the Native Gemini drivers built into TheSky6, then you need to use another program to boot the Gemini Control box before connecting TheSky6.  One such program is the one I supply with the adapter, called Rebooter.exe.   The second method is to use the ASCOM drivers using the Telescope API interface.  You have to install the ASCOM driver for version 4.  Go to the ASCOM site for details on ASCOM.

6.    Can more that one program be used to control the Gemini Control box, one connected to the normal RS-232 port and another connected to the Gemini USB Adapter or Gemini RS-232 adapter (Not in production anymore).
Answer: THESE ADAPTERS ARE NO LONGER AVAILABLE!  The ASCOM Gemini .NET driver now provides a way to have 2 programs control the mount.
Yes, but giving conflicting command to the Gemini control box would result in unpredictable results.  Using one program to control the mount, and another to monitor and get positions from the mount are fine.  One such possibility is TheSky6 to control the mount, and MaximDL for the camera control.  MaximDL can get the mounts position for the FITS header files.  I have not tested using MaximDL to do serial guiding through the serial ports while TheSky is in command of the mount. Another Possibility is running ASCOM type programs through one port and GCC theough the second port, It does not matter which is connected to which port. The Gemini has been tested with MaximDL/TheSky6 to one port and GCC to the other port. This works fine, as long as you do not command the Gemini to move with both programs at the same time.

7.   Can a Blue-Tooth adapter be directly connected to the Gemini USB Adapter?
Answer:  THESE ADAPTERS ARE NO LONGER AVAILABLE!  The ASCOM Gemini .NET driver now provides a way to have 2 programs control the mount.
No, USB-Blue Tooth adapters have to have software commands to configure them.  The Gemini does not provide these software commands. Almost all slave type USB devices have to have drivers to configure them. The Gemini USB Adapter requires drivers in the computer to configure it. Most BlueTooth devices also requires a driver to configure it. The Gemini USB Adapter cannot initial any type of communications device. It also does not provide power to power a BlueTooth device.

8.    Can a serial-Blue Tooth adapter be connected to the RS-232 Adapter? (NOTE: This device is no longer in production)
Answer:  THESE ADAPTERS ARE NO LONGER AVAILABLE!  The ASCOM Gemini .NET driver now provides a way to have 2 programs control the mount.
Yes, in fact I have tested both the AirCable and The Socket Serial Blue Tooth adapters.  Both work.  Using a normal RS-232 adapter either of the adapters have to have an external power source.  Using a Powered RS-232 that provides +5V on pin 9, no external power source is needed.  Please see Question 3 above about the Powered RS-232 Adapter
.

9.    Can the USB adapter be connected to a USB GPS Unit?
Answer:  No. All USB connections on GPS units are USB slave devices. USB slave devices require a USB master/host such as a PC to be able to initial them. The Gemini Adapter I sell is also a USB slave device. USB slave devices cannot talk to each other even if connect together through a USB hub. It would take very special software running in a USB master/host to pass messages back and forth between USB slaves. You can us programs such as GCC to get GPS data from a USB GPS unit connected to a PC, then have it update the Gemini with the GPS data. Also, the Gemini only interrogates and looks for a GPS unit out the 4 pin Telephone Style RS-232 port. Even if my adapter could connect to a USB GPS unit, the Gemini would not interrogate it for GPS data.

10.    What is a ground loop and how can you test for one?
Answer: A ground loop is a difference of potential in voltage between connected devices. It is normal to have a small difference due to the resistance in cables and connectors. However it should not be more than 1 volt in practice. Here is a good article that explains ground loops: Ground Loops Article
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Answer for how do you test for one.
Ground loops and power supplies are tricky thing. Take these steps to find out if you have a possible ground loop.
1. Turn off all power supplies. Leave the power supplies plugged into the house current.
2. Disconnect all power supplies from the Gemini and camera. Leave the one to the computer plugged in.
3. Measure with an ohm meter between the Gemini power pins of the VCD OUT GND pin (see page 131 of L4 manual) on the Gemini to the Ground pin of the Camera and then a ground spot on the Computer. Also measure between the camera and computer. A reading of NO ohms would be perfect. Any low reading could mean you might have a ground loop. This means that the power suppy input is not isolated from the power supply output.
4. Next turn all power supplies on. Measure for voltage between the ground outputs to each other. A zero reading is good. anything above 1 volt is bad. Voltage between 0 and 1 volt can also be bad, but depends on how large you wires are. Remember that you are doing this with no/very little current flowing.
5. Reconnect the camera, Gemini and computer. do step 4 with them connected. and see what you have. They should not have changed much. Again voltage between the units is a bad thing.

Computers can cause ground loops because they normally get connected to many other powered devices like monitors, networks and printers through wires.

The best way to eliminate ground loops is to have all the neutral (ground) DC output of every device tied to a central point, through a heavy (12 Gauge) wire. The central point when using a Gemini would be the Gemini ground input pins. This is not easy to alway do. The next best is opto or magnetic isolated inputs to the Guider and RS232 inputs.

If you do do a central ground between your devices, consider puting in a ground rod at least 8 ft deep next to the central point into the ground. This can help prevent static damage.

The best preventive is to use Isolated RS232 or USB adapters and Guiders into the Gemini. They can eliminate ground loops. I use one on all inputs to my Gemini. Of course I manufactured my own.

One word on note: The Gemini's with the slide switch for power do not have the electronics grounded to the case. The Gemini's with the Toggle switch do have the electronics grounded to the case.

11.     How do you disable the Gemini modeling, to use T-Point or ACP
Answer:  If using the ASCOM driver for your mount? Go into the driver setup and click first on the "Modeling Parameters" button. This should show all zeros. If it does not, click on "Clear Parameters" and store the clear out in your Gemini. Now go back to the main setup window and click on "Advanced Setup". In the top right of the window that opens you should see a check box with "Sync Mode Affects Model (Additional Align)". Make sure
this is UNchecked. Otherwise every time you do a sync you will be adding to a Gemini model which would adversely interact with the TPoint model. While you are in there, uncheck precession and refraction calculations, as TheSky does this itself.

12.     Is it possible to use more than one USB-serial adapter at one time on a laptop?
Answer:  Yes. You can use as many as you have USB ports. Please note that each one will be assigned a Serial port number according to which one is plugged into which port. Each USB to Serial Adapter has a unique serial number. So lets say that your first RS-232 adapter has serial number 2001 and your second has serial number 4001. Lets also say that you have 3 USB ports on your laptop called 1, 2 and 3.

Now lets say that you plug RS-232 #2001 adapter into USB port 1. The computer might assign it Com port 3,
Now lets say that you unplug adapter #2001 and plug in adapter 4001 into USB port 1, The computer might assign it to Com 4.
Now lets say that you plug adapter #2001 into USB port #2. The computer might assign it to Com 5.
As you can see, XP uses the adapters serial number and which USB port to assign the serial ports.

My recommendation is mark each adapter to which USB port you are plugging it into, and always use the same setup. That way you will continue to use the same predictable com port setting.

13.    How do you install the ASCOM Driver in TheSKY6?
Answer: If you downloaded the TeleAPI package from the ASCOM web site, Downloads section, Plugins, the zip file you have contains a ReadMe file that says:
This plugin allows Software Bisque's TheSky to communicate with ASCOM-compliant telescopes via TheSky's "TeleAPI" feature.

Installation

  1. Rename the file C:\Program Files\Common Files\System\TeleAPI.dll to TeleAPI-Original.dll
  2. Copy the ASCOM TeleAPI.dll to C:\Program Files\Common Files\System\TeleAPI.dll
One-time Telescope Setup
  1. In TheSky, Telescope menu, select Setup...
  2. In the Control System box, select "Telescope API"
  3. Click Settings... to open the ASCOM Telescope Chooser and select the ASCOM compliant telescope you wish to use.
  4. Now click Properties... in the Chooser, which will display the settings window for the telescope type you just chose. Make adjustments as your telescope needs.
  5. Close all windows including the TheSky Telescope Setup window by clicking OK or Close. Do not click any Cancel buttons.
Operation
  1. Make sure both your telescope and TheSky are set for the same geographic location and time.
  2. In TheSky, Telescope menu, select Link->Establish. You should see the cross-hairs indicating where the telescope is pointing.
  3. Please follow steps (1) and (2) exactly. The file does not go into "The Sky 6 folder in the program files"...
Also please see "Working With TheSky" on the ASCOM site (the link is in the text describing TeleApi) at http://ascom-standards.org/FAQs/TheSky.htm      (the above steps are a direct quote from Bob Denny in the ASCOM-Talk Users Group).

14.    How do you determine the Com Port of a connected USB to Serial Adapter and change it?
Answer:  These instructions work only for Windows XP.

15.    What is the different between the old and new autoguider ports?
Answer:  Directly from the manual:
4.2.1 The Autoguider Port.
IMPORTANT: There are two different versions of the Gemini Autoguider port hardware. The versions can be distinguished by the type of connectors used for the motor cables. The older Gemini version uses RJ-45 modular connectors, and the newer version uses 6-pin DIN connectors. The primary difference between the versions is that the older Gemini Users Manual 41 version does not directly support autoguiders with TTL output, but the newer version does. Gemini contains a separate Autoguider port  a 6-pin modular RJ-11 socket located below the 15-pin connector to the left. It contains a common pin, four directional pins and one pin that is controlled by the alarm signal that can be used for shutter control. The common pin of the RJ-11 modular connector is connected to +5V on the older version of Gemini, and GND on the newer version. The 4 directional inputs must be connected to the common pin to be active (they are active at High potentials on the older version of Gemini, and at Low potentials on the newer version). Simultaneously activating opposing directional signals (DEC+ and DEC- or RA+ and RA-) will be ignored and displayed as Autoguider Error.
Note: The autoguider port is only active in the Photographic Mode and All- Speeds Mode of the Gemini system. Selecting the Visual Mode disables Guiding and therefore the Autoguider Port.
More from the manual:

4.2.2 Manual Guiding
Manual guiding is usually done using an eyepiece with an illuminated reticle attached to an off-axis guider or separate guidescope. You center a star (or the object being photographed) in the reticle and use the buttons on the Deluxe Hand Controller to apply guiding corrections to keep the star on the reticle throughout the duration of the exposure. Rather than using the Deluxe Hand Controller, you can instead guide with a Losmandy Standard Hand Controller plugged into the autoguider port. The LED of the Standard Hand Controller will not normally be lit, but will light up anytime the alarm sounds. Using a Standard Hand Controller in the autoguider port has a big advantage for manual guiding, in that accidentally pressing opposite directional buttons simultaneously will not result in movement at centering speed, as happens with the Hand Controller in its normal socket, or when using the Deluxe Hand Controller. This reduces the risk of spoiling a long exposure photograph due to an accidental key press. In either case, you will need to make sure that the Hand Controller is set to either the Photographic or All-Speeds Mode.

4.2.3 Connecting an Autoguider to an Older Gemini:
4.2.3.1 Connecting an Autoguider with Relay Output
Autoguiders with relay outputs (such as the SBIG ST-4) can be connected to the Gemini system directly. Simply connect one side of each of the four relay contacts to the Autoguider input common pin, and connect the other side of each relay to the appropriate direction input pins of the autoguider port. Cables are available for most compatible autoguiders to plug directly between the autoguider and Gemini. Gemini Users Manual
42 4.2.3.2 Connecting an Autoguider with TTL Output:
The typical "open collector" output stage (e.g. the ST-7/8/9/10, user-modified ST-4) has high impedance while inactive and pulls down the direction signals to a common ground when active. This is exactly the opposite of the way the Hand Controller and autoguider ports of the older version Gemini system work. A relay (or optocoupler) decouples the switching device (the Autoguider) from the controlled device (the Gemini), thereby avoiding a direct connection between the two systems and protecting both systems against high currents that could cause damage.
IMPORTANT NOTICE:
(1) Never connect TTL output stages directly to the Hand Controller or autoguider ports of an older version Gemini! Severe damage may occur to the connected devices. Use a Relay Box (as provided by SBIG) or the optional Losmandy Optocoupler unit instead. By so doing, you get the additional advantage of providing electrical protection to these sensitive units. (2) The use of two separate power supplies without a coupler unit is strongly discouraged. To do so would connect the ground of one system to the supply voltage of the other system, causing the two grounds to be at different potentials. If the grounds of the two systems are then connected, severe damage is likely to occur. Detailed instructions for connecting an SBIG camera with TTL outputs to the older version of Gemini can be found in Appendix 8.6 (Autoguider Port). 4.2.4 Connecting an Autoguider to a Newer Gemini The Autoguider port on the newer versions of Gemini is plug compatible with a large variety of autoguiders. You can use an autoguider with relay outputs such as the SBIG ST-4 and STV or an autoguider with TTL outputs such as the SBIG ST-7/8/9/10 directly using the appropriate cable. Use SBIGs TIC cable for the ST-4 and STV, and SBIGs TIC-78 cable for cameras with TTL output. The SBIG relay box can be used, but is not necessary. The Losmandy Optocoupler is not compatible with the newer Gemini.
Also Note that the Common pin is not ground on the Newer style Gemini's. It is pulled to ground through a 100 home resistor. All the guider inputs are pulled to +5V through 3.3K ohm pullups.

16.    How do you get Windows 2000, XP, Vista & Win7 to show all the com ports that have been allocated?
Answer:   Windows does not normally show non-connected devices in device manager. This is even true if you turn on show hidden devices under the view tab. Before you do this change, be for warned - that this will let you modify/delete devices that you might not want changed or deleted. You do this at your own risk!. With that said here is a step by step process. You can also see how to do this on the Microsoft's web site at: http://support.microsoft.com/kb/241257.
For 2000 and XP:

  1. Right mouse click on My Computer and select Properties.
  2.  Select the Advanced tab.
  3.  Select the "Environment Variables" Button at the bottom above the "Ok" Button
  4.  In the "Systems Variables" box select "New"
  5.  A box will Popup that has 2 entry blocks.
    1. In the Variable Name: box enter devmgr_show_nonpresent_devices
    2. In the Variable value: box enter 1 then click the OK button , then click the OK button on the bottom of Environment Variables.
  6. Close the Hardware manager, and System Properites windows.
  7. Use step one above to reopen System Properites and select the Hardware tab.
  8. Select the Device manager.
  9. Under the View menu, select show hidden devices.
  10. Under Ports you should see all the devices that Windows has allocated now. You can modify them and delete them if you need, but please be careful what you delete.

For Vista/WIN7:
  1. Click in the Vista Ballon at the bottom of the page.
  2.  Right mouse click on Computer and select Properties.
  3. Select Advanced System Setting. If you are asked for permissions hit continue.
  4. Select the "Environment Variables" Button at the bottom of the page
  5. In the "Systems Variables" box select "New"
    1. In the Variable Name: box enter devmgr_show_nonpresent_devices
    2. In the Variable value: box enter 1 then click the OK button , then click the OK button on the bottom of Environment Variables.
  6. Close the the windows until you are back at the Control Panel > System.
  7. Select Device Manager
  8. Under the View menu, select show hidden devices.
  9. Under Ports you should see all the devices that Windows has allocated now. You can modify them and delete them if you need, but please be careful what you delete.
17.   What are the changes between L4V1.02 and L4V1.04 EPROMS?
Answer:  This version has the following updates over L4V1.02:
  1. Test for a defective autoguider input chip. Symptom: Gemini freezes after GPS readout. V1.04 checks this condition, a warning is displayed and operation is continued even if the chip is defective. A clearer explaination: Some brands of cameras, when un-powered and connected to the Gemini's auto-guider input, causes the autoguider chip/IC to give a failed condition on power-up of the Gemini., This does not mean that your Gemini is bad. It just means that there are unexpected inputs on power up. So don't send you Gemini back to Losmandy please. However if you are getting this message with nothing attached, then there is a very good possibility that your Auto-Guider chip is bad, and then you would want to contact Losmandy.
  2. Test for a defective serial port driver chip. A warning is displayed.
  3. PEC counter is restored correctly at a Warm Restart.

18. How do you determine if the RS232 chip in the Gemini is bad?/span> C21 in Gemini Controller
Answer:   Please read all this paragraph before attempting to test. The problem is normally with the negative voltage pump in the IC.  For some reason it seems to go bad. You can check this out if you have a good Voltmeter.  Please do this only if you feel comfortable doing this as you do it at your OWN RISK. The cap number is C21 in the newer boards with the round motor cables. Measure across this cap with you voltmeter with the Gemini powered up.  It is best if you have a friend do the meter reading while you hold the leads.  Micro-leads is highly recommended for this.  The lead closest to the IC is the negative lead. The side closest to the RJ22 connectors is the ground side.  This cap comes off of Pin 7 of the IC, which should be marked with 3221 if I remember correctly.  If you do not get a 5 Volt reading or close to that then the IC has gone bad (or been put to sleep, see note below) and needs to be replaced.  The Gemini is sensitive  to ground loops, and they can take this IC out.   This has been the problem in all the cases I have found except one. That had a bad cap and broken trace.  Please NOTE that this chip has an auto sleep mode that can also shut down the transmit part of the IC. If the IC has shut down the transmit part of the IC to save power, this voltage will also measure zero. To wake up the IC, ask the Gemini to get GPS data, or send it a command such as trying to connect using GCC. Any command that requires the Gemini to send a reply should wake the IC up.

19.  Can you run the Gemini without the motors connected safely?
Answer:   Yes you can power up the Gemini without the motors connected. You will get motor stall/stopped errors. You can stop these errors by putting the Gemini in the terrestrial mode.
Setup->>Mount Parameters->>Tracking Speed->>None/Terrestrial.
 

20.   What will cause the Gemini to shut down the handcontroller? F2 in Gemini Controller
Answer:   Micro Resettable Fuse F2 for Gemini. This fuse is a resettable fuse that protects the +5V circuit. If it drops to much voltage, the processor will shut down the +5V power supply in the controller. A symptom of this is the Gemini turning off the hand controller when plugging in a RS232 device into the RS232 Jack, or a Guider into the Guider Jack, or a GPS into the Feature Port. Basically anything that causes more +5V current drain can cause this symptom with a bad fuse.  In the older Gemini's it was Green and marked X14.   If your fuse is marked X14 and normally green in color, then you have the older fuse. The fuse shown in the picture is the newer higher rated fuse, but still green in color. It can be black in color and be the correct higher rated fuse. This was a known problem (according to René Görlialso ch ) and later units was shipped with the higher rated fuse to prevent this from happening.  All units shipped with the rocker switch should have the newer fuse.
 

21.     What does the red dots on the hand controller mean during boot?
Answer:  The characters at boot time indicate the boot progress and conditions
detected.

1st dot: internal resources and display initialized
2nd dot: power good, voltage stabilized
3rd dot: SRAM accessible (otherwise "SRAM failure !" will be displayed)
X: the content of the SRAM was reset to default values.
R: RTC was reset ("RTC malfunction" displayed if RTC is not
working)
4th dot: RTC initialized
5th dot: SRAM values loaded.

"AG port defect ? " will be displayed if one or more AG signals are active.

The X is to be expected after a version change, battery change, at low
battery voltage and so on.
Once it appears, a "CMOS reset" string is appended to the startup
message, too.
Since the initializing is done by the same subroutine as used by the
Setup...Reset Defaults menu point,
there is no need to take the battery out to renew the SRAM content.

A side effect of pulling the battery out is that the RTC chip will stop
working after a while and may then be
initialized at the next startup. In case of problems you may first check
and maybe set the UTC date and time and the ALARM time, too.

If the second dot is not displayed and the boot process stops, the board
voltage does not stabilize at the nominal 5V voltage and F2 may have to
be replaced. Try to remove peripherals in this case (AG, serial
connection, feature port peripherals, axes encoders may draw too muc
current) and boot again.

There is a unused connection from the battery to an analogue input pin
of the CPU to check the voltage - R32 was removed since the CPU chip
drew some current from the battery while being powered off, shortening
battery life.

The above answers are a direct quote from René

Also there is another known problem, which is C3 a 4.7uf 10Volt cap directly above the processor.   This cap is what resets the Gemini processor at power up. It is suppose to hold the Processor in reset while the power stabilizes.   If it is not holding the processor in reset long enough, then the processor might not be starting up correctly.   A quick test of this is to take a pair of fine needle nose-pliers/tweezers and short across this cap for about 1/2 sec.  Then remove the pliers/tweezers.  If the Gemini then boots ok, it could be an indication that this cap is loosing it value, or it's pull-up resistor R45 (a 10K) value has also changed. This cap has also been known to break aloose from the circuit board.

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