DMP-100

Radio Shack DMP-100
Radio Shack LP VII

Engine/OEM

Seikosha/Axiom GP-100 (Ribbon: GP-20050)

Other printers based on the same engine

• Seikosha/Axiom GP100TI II (TI-99/4a) / GP-100AT (Atari)
• C. Itoh Riteman C+ F+ F+11, Prowriter Jr. Jr+, CI 6024
• Gorilla Banana
• Leading Edge GX-100
• Commodore VIC 1525
• Alps ASP 1000 / 1600 / PTSWA 10
• Amstrad DMP2000 / DMP2160 / DMP3000 / DMP3000D / DMP3160
• Spectravideo SV-901 / SVI-901

Ribbons

TANDY 26-1424

• https://www.ebay.com/itm/355024310435 (just the ribbon loop that you install into original housings)
• https://www.ebay.com/itm/352159160382
• http://www.scantracker.com/C_Itoh_printer_ribbon_RP-204.html
• http://www.inkcartridges.co.nz/amstrad-dmp2000-dm3160-printer-ribbon
• http://www.dotsplus.com/item.asp?id=200&desc=amstrad-riteman-c-ribbon (6-pack for $30!)
• http://www.aroundtheoffice.com/C-Itoh-Printer-Ribbon-RP-204-ITO/productinfo/RP-204-ITO/

Other possible printer or ribbon matches

Not sure about these.

C. Itoh Gx100

Seikosha/Axiom GP-80 (ribbon GP-08050)

Commodore VIC 1515 (GP-80 vs GP-100?)

Seikosha/Axiom GP-250X

Alpha Matrix 2100

Manuals and other info

https://archive.org/details/DMP-100_Operations_Manual_19xx_Tandy
https://colorcomputerarchive.com/repo/Documents/Manuals/Hardware/DMP-100%20Service%20Manual%20(Tandy).pdf
http://www.ti99iuc.it/web/download.php?fn=_archivio/167/download/AXIOM-GP100_Printer%20Interface-Manual(Eng).pdf
http://www.avdcs.com/prod/dotm/do_cons/do_cons.html

Re-inking an old ribbon

You can re-ink old impact ribbons with oil-based stamp pad ink.

"Stamp pad ink" comes in both water(glycerine)-based, and oil-based versions. Make sure to get oil-based.

Original dot-matrix ink was oil-based because, aside from not drying out, the oil in the ink was necessary to lubricate the pins in the print head.

The lubrication probably is not important in the specific case of DMP-100, because although the DMP-100 is a dot-matrix printer, it does not use pins to make the dots.
DMP-100 uses a single hammer with a vertical line like a single typewriter letter |, that intersects with a raised horizontal line on the platen behind the paper.
The intersection makes a dot, and both platen and hammer move to create a grid of dots. But you still want the same oil-based ink anyway.

A few drops is a lot, and it takes time for the ink to spread and soak evenly.
There is no reservoir of extra ribbon in the housings, just a loop that is exactly the length of the mechanism.
Instead there is a sponge wheel in the right-side housing which continuously re-inks the ribbon.

The housing is not held together with either glue or snaps, just friction-fit pins.
You can use an xacto knife to lift up the top half of the housing easily without damaging anything.
Then just add a few drops of ink to the sponge and snap the housing back together.
The sponge wheel can fall out of alignment and it can take some wiggling to get the top to snap back into place. You may need to slip the xacto knife in and use the back side of the blade to nudge the shaft of the sponge wheel one way or another.
Then just use the printer a little to cycle the ribbon.

C. Itoh ribbon hack

This is only if you are desperate and cannot aquire the correct ribbon.
If you have a dried out ribbon, KEEP IT, and re-ink it.
If you have a worn-out ribbon that is not merely dry but the fabric is physically disintigrating, STILL KEEP IT,
because sometimes there are people who sell just the loop of ribbon the right length and you can install that into your housings easily.
If nothing else, plain 5/16" "adding machine ribbon" is still available and that could be used to make a new loop, assuming there is a way to splice the ends.
But failing all of that, there is another ribbon that is similar enough that it can be hacked to work.
It really is a hack.

Photos of C. Itoh ribbon to DMP-100 hack:

https://goo.gl/photos/4qmiSC5xp8QpQio18

Preparing the ribbon:

When you buy the ribbons new, they have some clips formed into them that don't fit the DMP-100.

Shave all clips and bumps off to make the bottom and sides flat. You don’t have to modify the tops. The plastic is soft enough that it's not too hard. I use a multitool to break most parts off by grabbing them with the pliers, then clean up a little by shaving with the knife and maybe the file. The fat pin in the center of one of the housings is a bit tough to get with a knife alone, so you may have to use the saw on that.

Put about ¾ inch square of 3M automotive double stick foam tape on the bottom of each housing. Leave the red plastic film on for now.

Installing the ribbon:

Use some alcohol and paper towel to clean the top surface of the steel platforms where the normal ribbon housings go, so they are clean and dry.

Peel off the red plastic film from the housings.

Take the larger housing with the round shape and the bump on top in your Left hand, and the smaller housing with the flat blade on top in your Right hand, and stick them to the steel platforms, butted right up against the inside walls of the printer, and such that the ribbon closest to the front of the machine forms a straight line through the ribbon advance pincher behind the print head. The ribbon that touches the paper will not form a straight line. You should feel a ribbon tension spring compress a little in the right-hand housing, and the ribbon should have no slack. (route the ribbon in front of the print head and through the ribbon advance pincher the same as normal)

3m adhesive foam will stick well enough to print immediately. It will become stronger over time, but can still be peeled off (slowly) later, with no damage to the printer.