I've searched high and low for a driver & a manual for you for this printer but no joy out of 30 seperate search engines. Unless someone has better luck than me I'd suggest you trade this printer in and get yourself a modern upto date model, you can't go far wrong with Epson or Cannon and drivers are readily available for both these models from a wide variety of online sources.
Well I did another search, took about an hour using no less than 100 search engines and found plenty of dead ends, mainly Juki Sewing Machines and screen printers the size of houses. Looks like the printer in question goes way back towards the late 80's early 90's and although I came across lots of questions posted on various forums about Juki 7100 drivers no joy what so ever. It appears you can still get printer ribbons for this model but as for a working set of drivers for up to date operating systems you'll be lucky, however, HWC is a well read Forum so maybe, just maybe a Juki 7100 owner with a set of drivers might read your post!
Juki 7100 is color matrix printer from stone age! I've owned one time ago, and it worked fine with Commodore AMIGA 1200 (1992 year of production). I've used standard Amiga's "Epson ESC/P driver" for grayscale and color.
I guess it has an issues with "port speed", i.e. old computers with "slow" parallel ports talk normally with this printer, but newer PC's parallel ports are sending data faster than Juki 7100 could accept, so it didn't print with ANY driver on ANY 486+ PC
...or you could try connecting this printer to PC's serial port with low baud-rate (i hadn't try this variant, i've found that it has not only centronics but also serial port an hour ago...)