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Old 13th Mar 2018, 11:56 pm   #1
ct92404
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Question Star Gemini-10 printer

I recently found a Star Gemini-10 dot matrix printer. I wanted to hook it up to my Tandy 200 computer. Unfortunately, I'm having some weird problems with the printer, and I can't even find any information about this specific model. I'm hoping someone might be able to help.

When I first got the printer, it did respond but wasn't actually printing text even after I put in a new ink ribbon. I cleaned the print head and now it is printing...but there's another bizarre problem. When I had the printer do a self-test, it looks like it's printing two characters together, one on top of the other! What I mean is that it looks like two lines are getting run together. The platen does turn and the paper seems to be advancing the way it's supposed to. So I don't understand what's happening. It also has the same problem when I try to print text from the Tandy 200.

I'm wondering if a dip switch is set wrong or (hopefully not) a chip in the printer is bad.

I haven't had any luck trying to find a manual for this specific printer. I found ones for the Gemini-10x, but not mine. Mine is just a Gemini-10, not a 10X. The 10X looks nearly identical to mine, but the manual for that one refers to dip switches that this printer doesn't seem to have. I've looked everwhere on it and even took off the cover and I've only found one set of switches.

Does anyone know anything about this printer and what might be wrong? I really like the fact that it uses an ordinary typewriter ribbon which is surprisingly easy to get. I really hope I can get it to work.

- Chris
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Old 14th Mar 2018, 3:08 am   #2
arjoll
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Default Re: Star Gemini-10 printer

Quote:
Originally Posted by ct92404 View Post
When I had the printer do a self-test, it looks like it's printing two characters together, one on top of the other! What I mean is that it looks like two lines are getting run together. The platen does turn and the paper seems to be advancing the way it's supposed to. So I don't understand what's happening. It also has the same problem when I try to print text from the Tandy 200.
Does it advance at all when printing, or only when pressing line feed?

If it doesn't advance when printing, look for a DIP switch that controls adding a LF to an incoming CR. Some systems sent both, some only sent CR. Having the switch set wrong would mean either overprinting on one line until a FF was received, or double-spacing everything.
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Old 14th Mar 2018, 4:33 am   #3
ct92404
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Default Re: Star Gemini-10 printer

The paper does advance when it prints.

I'll see if I can get a picture of what a printed paper looks like. It's really strange!
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Old 14th Mar 2018, 5:32 am   #4
ct92404
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Default Re: Star Gemini-10 printer

I'm attaching a picture of the printer, and and a paper that it printed with the self-test.

It might be kind of hard to see, but for some weird reason it's actually printing characters twice. You can especially see it on the last line, where it prints "H I J K L N O P" and it prints them twice, one on top of another. At first I thought it was some kind of mechanical problem, that maybe the pins in the print head weren't aligned right or something. But then when I looked at the paper more closely I realized that it is printing distinct characters, but it's just printing them twice vertically for some strange reason. The problem seems to be electronic, not mechanical.

Any idea what could be causing this?
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Old 14th Mar 2018, 9:35 am   #5
McMurdo
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Default Re: Star Gemini-10 printer

Reminds me of the old epson printers that could be set to double-print each character to make the text stand out. The effect was more pleasant than the mess in your pic though!
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Old 14th Mar 2018, 9:52 am   #6
G6Tanuki
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Default Re: Star Gemini-10 printer

From memory, the printhead-movement on these kind of printers is by a long toothed belt and a stepper-motor. There's also usually some form of absolute-indexing mechanism [a phototransistor/LED assembly) at each end of the printhead-runners to set the end-points and to stop the thing mashing the printhead against the end-stops if you didn't include a carriage-return!

Some similar printers used a slotted optical-disc 'chopper' to sense the printhead-drive's rotation & movement as it proceeds along the rails.

In either case check the optical sensors are clean and free of dust/cat-hair, and also the condition of the belt/stepper-motor: if the stepper's being advanced by the software but the slotted-disc isn't recognising the fact that the carriage should have moved forwards so the next character is to be printed, it can get confused because it hasn't completed the 'print current character' cycle fully, so it prints it again.

If the drive-belt's gone stiff with age, or if the stepper-motor's toothed sprocket has grot in its teeth, this could cause what you're getting too.
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Old 14th Mar 2018, 11:22 pm   #7
mike_newcomb
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Default Re: Star Gemini-10 printer

Hi Chris,

from no print, following cleaning the Print Head you appear to have only partly solved the problem.
I would try further cleaning, such as soaking in IPA.

Am sure I had that Printer only differently badged. Think it came with three print modes, draft, nlq and letter quality. The test print could be demonstrating these, and others such as Bold, Enhanced etc. which would explain why some print is doubled up.

Is the Interface, serial, parallel or both?

Regards - Mike
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Old 14th Mar 2018, 11:50 pm   #8
ct92404
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Default Re: Star Gemini-10 printer

Thank you everyone for the replies and advice so far.

Mike, the interface has both serial and parallel interface. I connected it to the Tandy 200 with a parallel connection. (I think the printer needs another part to be able to connect it with serial).
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Old 15th Mar 2018, 6:12 am   #9
JohnBHanson
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Default Re: Star Gemini-10 printer

What I think is happening is as follows

Each line of print requires two passes of the printhead
The first pass from left to right prints the odd numbered rows of dots
The paper then moved down one dot height
The second pass from right to left prints the even numbered rows of dots.

There is some slackness in the belt from the steppermotor to the printhead so that
the printhead is not in the same horizontal position when printing left to right as right
to left.

Hence you get double characters - half the letter on the left to right pass, and half the letter on the right to left pass, but as these are not in the same place you get the strange effect.

I hope that makes sense.
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Old 15th Mar 2018, 7:28 am   #10
mike_newcomb
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Default Re: Star Gemini-10 printer

Hi Chris, have you seen:-

https://www.star-m.jp/eng/dl/dl01_02.html

It appears the Printer's User Manual is there in two parts.

(from memory) the Parallel Port was standard on the the mobo. The Serial Port was an add on card, which had its own dip switch bank or banks for setting baud rates etc.

Regards - Mike
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Old 15th Mar 2018, 8:16 am   #11
ct92404
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Default Re: Star Gemini-10 printer

Mike, that's for the Gemini 10x, whereas mine is just a Gemini-10.

They look nearly identical, but the manual for the 10X refers to two sets of DIP switches (DIP 2 at the back of the printer, and DIP 1 inside.) I've looked everwhere on my printer and I've only been able to find one set of DIP switches, at the back.

It's really weird, but I can't find any information or manuals on my particular model at all! Mine is definitely a different model, because it's labeled Gemini-10 whereas the 10X specifically says 10x and also has another silver Star label on the front that mine doesn't have. At first I thought they were close enough, but there must have been some changes and I can only find one set of DIP switches on mine (which has 4 switches).

I'm really stumped. Maybe the regular Gemini-10 wasn't made for very long?
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Old 15th Mar 2018, 1:40 pm   #12
mike_newcomb
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Default Re: Star Gemini-10 printer

Hi Chris, did you remove the Upper Casing?

Pages 49-53, and 262 (actual - not pdf page numbers) describe / picture the dip switches including their locations. In order to access DIP Switch one, requires removing this.

I think the Serial Port pcb came with its own manual, which included its dip switch settings.

User maintenance for this TYPE of printer is simple. With the power disconnected:

a) with the Upper Casing removed, blow out any dust etc. with a Hair Dryer set to cold and maximum blast, Use a long thin soft (childs paint?) brush to assist.

b) the print head moves on one or two rails and generally has bronze or similar bushes.
Remove any dust wads that have built up.
Manually Position the Print Head in the centre of its run.
Place a single drop of quality (eg Singer Sewing Machine or Razor) Oil either side of the print head, on top of the rail(s).
Slowly move the Head to its left and right limits a few times.

c) as you found the printer, check there is nothing inside the parallel or serial ports that might interfere with a signal.

It is worth remembering when these Printers were made, the www did not exist. Thus lengthy Printed Manuals were supplied, packed with information, often similar in size to 'War and Peace'

Regards - Mike
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Old 16th Mar 2018, 6:35 pm   #13
GeoffB17
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Default Re: Star Gemini-10 printer

Hello,

I've still got my G-10x, and the manual, and the printer still works - as far as the dried-up ribbon will allow. Some WD-40 on the ribbon usually helps.

Firstly, I think the 10 and the 10x will be similar. I note the lid/cover is different regarding thetractor 'hump' mind you.

On mine, I have the optional SIO board - however, there is an internal connector (flat cable) that needs to be moved to swap between SIO and Pll operation.

Regarding the print, it looks like the sort of thing that happens when there's a problem with the pll cable, but if you're doing the self test, that should not apply. BUT, there is another flat (pcb type) cable that connects the main board with the print head, and this is getting constant flex while the printer is operating. If one of the tracks is damaged, or the cable is damaged so that two lines are shorted, this may also cause one or more pins to fire when they ought NOT to?

Oh, my printed manual is NOT the size of War & Peace! It's book dimensions, but ONLY 262 pages. DIP switch guide is on page 262.

DIP Sw 1 default position is all 8 switches are ON

DIP switch 2 has 4 switches for:
No Paper Detection ON
Buffer Full Print OFF
Bit selection OFF
Automatic Line Feed OFF

The notes regarding setup for use with specific computers includes changes to certain DIPs depending on the computer used.

Oh, my manual is dated 7/84. Yes, I've now found the separate SIO instructions.

Checking your print example..

The bottom pin, which should fire ONLY for underline, or for some descenders for some lower case letters like g and y, seems to be firing almost all the time. Also, one of the middle pins is firing INSTEAD of one of the higher pins. Various pins seem to be firing correctly. I'd have a VERY close look at the cable connecting the head to the main board, and the crimp connector at each end.

Geoff

Last edited by GeoffB17; 16th Mar 2018 at 6:55 pm. Reason: Add extra info
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