About the Panasonic one:
It sounds like a defective cable to me. Check this things:
- Most printers have an internal test page, so print it. It should be triggered by powering the printer while a key is held (i.e.: Power + Line Feed), refer to your manual. If that page is fine, the trouble is outside the printer. If it fails, you have some kind of board problems.
- Go to command prompt and type COPY CON LPT1 (or your printer port). Write some characters and press intro. Write some characters more and press intro. Then press control+L and control+z. The characters should be printed. If they match, you have problems with your driver; if they don't match you have some kind of problem with your PC port, your cable or your printer port. Repeat the test with another cable and/or PC (BTW, AFAIR, ctrl+L means "eject page" and ctrl+Z finishes the character input and returns to command prompt).
- If your printer fails even after using a good known cable, I'd suggest to check your port connections and traces in the printer board... maybe they've shorted or are broken.

About the Gorilla one:
It looks like a mechanical failure to me. Maybe a motor is faulty (do you hear a motor trying to move something?), maybe a sensor is dirty and the printer thinks it have a fault. Try to clean that printer and get a service manual...

About both printers:
Every Windows version since 3.11 have a "Generic / Text Only" printer driver. It is not very useful because it won't print graphics, but it is useful to do some checks. It is the equivalent to the COPY CON thing, and it should work with every dot matrix printer.

Thanks for the info; self-test works just fine. I'm somewhat relieved. I love that old printer.
Gonna try the copy con thing in a minute.

okay, I went into the case, tried a printer card which didn't work at all... unplugged and replugged the cable switched to 278 from 378 interrupt...
Don't think the interrupt change was necessary; I suspect that somehow, in working on other cables the printer cable came partially detached from the motherboard.

The Panasonic 2130/2135 works fine now.

Tomorrow I plan on opening up the Gorilla Banana. I really hope I can get it working; it was comparatively rare, I believe, but for some perverse reason I desperately want to create / see 7-pin printouts with their lack of descenders. I'm hoping it's a cable I can replace or some silicon grease I can apply or just a sharp tap I can give that will get it working again.