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Hello all,

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I'm the proud new owner of an old G11? from 1995running Gemini 1. To get it working almost like new, I had to re-grease it, replace the polar scope, and decided to reduce the default motor speed to 600 to preserve what's left of them. I've taken a few months to validate the setup using either the controller or a small Mele computer running NINA, PHD2, stellarium and now FireCapture for planetary imaging. It all works like a charm with decent guiding for my C11 or CFF 105mm refractor, including meridian flips—GREAT!

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As a precautionary backup, I got my hands on a second Gemini 1 with the same old motors at a good price. However, I'm still trying to get this one to work, as I've had issues with the RTC. I replaced the CR2354 battery with a new one that reads 3.3V. The location, mount type, and other settings all work well and remain in memory with no issues. However, the RTC wasn't functioning correctly. Initially, it displayed an RTC error and erratic time displays with symbols like "?" and "#", along with numbers. I decided to replace the RTC63421A with a new one.

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Now it's better: I can set the correct time, but the RTC doesn’t run consistently. Sometimes it stops, sometimes it blocks the controller, at best it runs at about 1/3 the normal speed (i.e., seconds only update every 3 seconds). I’ve attached a photo of the main board. Nothing looks fried to me, so I’m stuck. Any ideas about what might be happening or how I could troubleshoot further?

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Many thanks, Franck

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Hi Franck

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Here’s a few possibilities:

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1: The RTC put in was probably 2nd hand or at worst “counterfeit”. ? The only sources of these can be good or …..dreadful! ? Sometimes it’s a lottery. ?If you’re other Gemini 1 has this IC in a socket. ?Try swap them. ?Pls use ESD precautions.?

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2:SRAM does have locations for RTC data the SRAM may be damaged. ?This is a high possibility I have seen similar before. ?Loses some data but not other!

3: The CPU (and HC display(s)) converts or determines HC data to Characters displayed. ? ?It’s possibly a bad CPU. ? ?Swapping CPUs …again observe ESD precautions. ? You need a PLCC IC puller. ?

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4: ?Lastly the HC displays interpret data streams and with inbuilt controller helps convert this to characters. ?Easily checked. ? ?Swap them….?

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The above, in order are all possibilities of fixing the issue starting at most probable to least.?

It’s a little hard to say. ?Since the RTC and CPU are easily changeable, one usually goes for easiest possible fix first. ? ?

But…..I kinda get the impression it’s SRAM!

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Anyway FWIW, definitely try plug-in swappable ICs first before touching SRAM. ?You can ohm out SRAM and RTC pins to each other and gnd to check for any glaring abnormalities.?

FWIW cheers, get back on how you go or if you need more assistance.?

cheers

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Brendan

And welcome. ? Good to hear G1 users and that these venerable units will outlive us and be handed on!

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Wonderful equipment and mounts.?

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Brendan

Annnd I should have said check battery voltage is getting to the SRAM/RTC thru D1.?

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Maybe check diode D1 with ohmmeter on diode function. ? Check it switches ok to around 4.9V dc ~minimum ?at SRAM/RTC at same point mentioned above when system powered on!

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Sorry just brain storming ….my thoughts are all over the place line a dogs back leg!

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cheers

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Brendan

Thanks so much, Brendan—just what I was looking for. I'll carefully go through your suggestions and take a look at D1 as well. I'll let you know once I make more progress with the troubleshooting.

Franck