Northern Telecom Displayphone Firmware ROMs and Information

This page is intended to collect information about the Northern Telecom Displayphone terminal. If you have any additional information about the Displayphone, please leave a comment. I’m specifically looking for later revisions of the software found in EPROM on these machines.

If you need to familiarize yourself with the unit, have a look at Dave Dunfield’s Displayphone site.

Displayphone Models I’ve Had

I have encountered two types of Northern Telecom Displayphones:

  1. The regular Displayphone (model NT6K00)
  2. The upgraded Displayphone Plus (model NT6K90)

Displayphone Manuals

Displayphone Keyboards

I’ve seen the regular Displayphone NT6K00 with both the small chicklet keyboard as well as the upgraded keyboard. The Displayphone Plus NT6K90 I’ve only seen with the upgraded keyboard.

Displayphone Firmware Revision ROMs / EPROMs

Software in a Displayphone resides on EPROMs that are accessed by removing a trap door on the bottom of the unit.

Displayphone NT6K00 Firmware

I have encountered two revisions of firmware for the Displayphone NT6K00. The firmware is stored on five 2764 (8 kilobyte) UV EPROMs. In my testing of one machine, one ROM had failed with 5 bytes failing checksum.

Correct 16-bit checksum value appears to be the last two bytes of U49 ROM in little endian.

  1. Version “AA07” with the checksum of 4601 (hex). 1982 or 1983. Download Displayphone ROMs AA07 (26 kilobyte ZIP file)
    • U45, QQ6WM, A0298294
    • U46, QQ6WN, A0298295
    • U47, QQ6WF, A0298296
    • U48, QQ6WQ, A0298297
    • U49, QQ6WR, A0298298
    • Note: This version appears to disable the external (or “local”) RS-232 port in firmware and therefore not very useful.
  2. Version ” 6V0″ (there may be a space to the left of the 6) with checksum 5652 (hex). Download Displayphone ROMs 6V0 (25 kilobyte ZIP file)
    • U45, A0295041
    • U46, A0295042
    • U47, A0295043
    • U48, A0295044
    • U49, A0295045
  3. Version “AA05” dated Nov 1982 sent by Andrew (see comments below) with checksum of 0C70H (hex). Download Displayphone Roms AA05 (24 kilobyte ZIP file)
    • U45, QQ4BT
    • U46, QQ4BU
    • U47, QQ4BW
    • U48, QQ4BX
    • U49, QQ4BY

Displayphone Plus NT6K90 Firmware

I have encountered one revision of the firmware for the Displayphone Plus NTK690. The firmware is stored on three 27128 (16 kilobyte) UV EPROMs and one 2764 (8 kilobyte) UV EPROM.

  1. Version “VT01B” with unknown checksum. Unable to verify if ROMs are valid, machine will not power up properly. Download Displayphone Plus ROMs VT01B (41 kilobyte ZIP file)
    • U31, VT01B 3, “21 MAR. 85”
    • U32, VT01B 2, “21 MAR. 85”
    • U33, VT01B 1, “8 MAR. 85”
    • U34, VT01B 0, “11 MAR. 85”

Performing a ROM Checksum

Perform a ROM firmware checksum on your Displayphone with the following key combination:

  1. Press SERVICES.
  2. Press zero on dial pad.
  3. At PASSWORD? prompt, hold SHIFT and press C on keyboard

Clearing Displayphone Memory

After each power on, you should clear the memory of your Displayphone with the following key combination:

  1. Press SERVICES.
  2. Press zero on dial pad.
  3. At PASSWORD? prompt, press 7 then 8.

Displayphone Power Supply

The Displayphone power supply is a triple voltage box-on-leash style brick with permanently attached cables. The plug that goes to the Displayphone is a DE9 female. I’ve encountered both a metal case and a plastic case style power supply.

The plastic style case (model NT6K01AA) is 110 VAC, 0.50 A input and has output ratings listed as:

  • +5V at 2.0 ADC
  • +12V at 0.8 ADC
  • -12V at 0.1 ADC

The power supply DE-9F pin out has been visually determined as follows (along with the cable color used on the NT6K01AA PSU).

  • Pin 1: +5V (white)
  • Pin 2: +5V (yellow)
  • Pin 3: N/C (purple)
  • Pin 4: +12V (orange)
  • Pin 5: N/C (red)
  • Pin 6: -12V (brown)
  • Pin 7: N/C (green)
  • Pin 8: Common (blue)
  • Pin 9: Common (black)

Opening the Displayphone Case

If anyone has any tips or pointers on how to open the Displayphone case, please leave a comment.

Update: Andrew confirms (in the comments below) to open the Displayphone case, you need to insert a tool into the back of the case to release an internal tab. Andrew used a multimeter probe.

Update: @TubeTimeUS has posted pictures of the take apart process including discovering there is a battery inside that leaks. If you have one of these units, you’ll want to remove the battery ASAP, clean the board, and examine for any damage.

29 thoughts on “Northern Telecom Displayphone Firmware ROMs and Information

  1. Permalink  ⋅ Reply


    August 2, 2018 at 2:21pm

    Any chance you have the pinout of the power supply?

    • Permalink  ⋅ Reply


      August 2, 2018 at 9:59pm

      Power supply pin out added.

  2. Permalink  ⋅ Reply


    August 8, 2018 at 2:12pm

    Thank you. You have made my life much much easier.

  3. Permalink  ⋅ Reply


    March 15, 2019 at 8:27pm

    Did you ever figure out how to open the case properly?

    • Permalink  ⋅ Reply


      March 15, 2019 at 11:04pm

      Unfortunately no. I suspect it’s a tool inserted into the small hole on the back that releases a tab, but I’m not certain.

      • Permalink  ⋅ Reply


        March 16, 2019 at 5:05pm

        Looks like you’re right, I shoved a multimeter probe in the hole and it is now coming apart πŸ™‚

    • Permalink  ⋅ Reply


      March 17, 2019 at 8:14pm

      Now that I have the DisplayPhone working it is firmware version AA05, checksum is 0C70H which passes the internal check. Both internal lines are enabled and working as well as the local RS-232 port.

  4. Permalink  ⋅ Reply


    December 6, 2019 at 3:33pm

    Thanks for the power supply pinout. I have one of these (acquired from Data General) and I had misplaced the power supply. Now I can donate it (with power supply) to the Connections Museum in Seattle.

    I used it for a long time as a phone and terminal in my workshop. A bit clunky (the handset cord kept getting tangled with the keyboard), but really neat for the time.

    Of course, now, we have iPhones πŸ™‚

  5. Permalink  ⋅ Reply

    Dan Meyer

    December 17, 2019 at 5:32pm

    Just acquired a Displayphone 1000, any resource material or helpful info for it?

  6. Permalink  ⋅ Reply


    June 15, 2020 at 6:27pm

    used to work for Nortel and have two dispay phone versions one is the larger screen that swivels. trying to get my NT6k90 working again so i can use it for packet radio.

    think my roms are shot.

    • Permalink  ⋅ Reply

      Dan Meyer

      September 21, 2020 at 3:20pm

      I’ve been looking for info on the larger Displayphone with the monitor that swivels, I have one as well. Do you have any manuals or information for it?

      • Permalink  ⋅ Reply


        March 13, 2021 at 8:16pm

        I have a NT6K90 that seems to be functional but cannot enable the RS232C port. is this disable or is there a trick to it? It shows up in menu, but no softkey to enable the port.

        • Permalink  ⋅ Reply


          March 13, 2021 at 8:46pm

          Certain ROM revisions disabled the RS232 port. You may be able to burn new ROMs to enable the port.

  7. Permalink  ⋅ Reply


    March 4, 2021 at 9:16am

    Were these able to communicate without going through a BBS— just connect direct through phone line?

    • Permalink  ⋅ Reply


      March 4, 2021 at 1:09pm

      Yes, a built in modem allowed you to dial into another system. They also have a RS-232 port on the back to directly connect to a system or another modem.

  8. Permalink  ⋅ Reply


    March 13, 2021 at 8:14pm

    I have a NT6K90 that seems to be functional but cannot enable the RS232C port. is this disable or is there a trick to it? It shows up in menu, but no softkey to enable the port.

  9. Permalink  ⋅ Reply

    James Wade

    October 17, 2021 at 5:05pm

    I have an NT6K00, and the AA07 BIOS seemed to be corrupted. After a few days of it sitting turned off but plugged in, when turned back on the text on screen would appear as gibberish. The BIOS passed the checksums. I was able to remove the access hatch on the bottom and gain access to the EEPROMs. I was able to remove them, flash them, and program the 6V0 BIOS which allows for the RS-232 port to now function as well. It seems to have fixed the issue of garbled text. If anybody needs help with BIOS issues, I may be able to lend some assistance.

    Does anybody know how to hook some phones together using an RS-232 cable to send messages, and might anybody have an NT6K00/90 that they may be willing to part with? Is a Null Modem needed, or do they hook up directly? I was born in 1994, so I have very little knowledge about this technology even though it fascinates me greatly. Any help would be much appreciated πŸ™‚

    • Permalink  ⋅ Reply

      Leonard Wolf

      November 14, 2023 at 1:41am

      I have a NT6K90 that seems to be functional but cannot enable the RS232C port. You mentioned an alternative BIOS that allows the RS232 Port to be enabled? Is there a link or an on-line location where I can download the BIOS you installed?

      • Permalink  ⋅ Reply


        November 14, 2023 at 4:59pm

        My NT6K90 will not power up so I can’t verify what the VT01B ROMs in my machine actually do. You can try the VT01B ROM I have available here (scroll up, the download link is on the same page).

        If you have different ROMs, I encourage you to dump the ROMs and send them to me.

  10. Permalink  ⋅ Reply


    December 4, 2021 at 6:40pm

    I have NT1k00AA / part c2501590 I don’t have any cable .. if anyone interested to buy let me know ..

    • Permalink  ⋅ Reply


      January 12, 2022 at 7:44pm

      Hi Tashi. What is that particular device?

  11. Permalink  ⋅ Reply

    Nathan Byrd

    August 24, 2022 at 8:24am

    I was just able to get a DisplayPhone NT6K00 but without a power supply that is supposed to arrive today. I’m working on converting an AT power supply to work, but was hoping to get a bit more clarification – when you are numbering the pins on the DE-9F are you referring to numbering from the top right when looking at the female plug like if you were numbering for RS-232? So, for instance, the two top right pins are +5V and the two bottom left are common? I hopefully can figure it out based on tracing the ground pins, but was also hoping you might remember as well.

    • Permalink  ⋅ Reply

      John Viverito

      December 20, 2022 at 8:50pm

      Hi Nathan,
      Pinout looking into a
      DE-9F: (pins numbered right to left)
      5 4 3 2 1
      9 8 7 6

      DE-9M: (pins numbered left to right)
      1 2 3 4 5
      6 7 8 9

  12. Permalink  ⋅ Reply


    August 31, 2022 at 1:28pm

    Anyone know if there are substantial differences between firmwares 6V0 and AA05? I just got a new-in-box Displayphone with version AA07 and need to switch to a firmware that enables the serial port.

    Thanks & thanks for having this website, it’s been a huge timesaver!

  13. Permalink  ⋅ Reply


    December 3, 2022 at 6:31pm

    I was at a local CO and found one of these!!! Def 80’s retro!! I plugged it in and could not believe how cool this looked. This is the NT1k00AA model (Not plus)

    Its sitting in a cabinet gathering dust.

    Is there any diff from the orange display or White display?? Mine is Orange….

  14. Permalink  ⋅ Reply

    John Viverito

    December 20, 2022 at 8:38pm

    Hi All,
    I’m an old Northern Telecom Tech. In need of a power supply (nt6k01aa) for my Displayphone. I have it on display in my office. Looks cool. Just doesn’t have power. πŸ™

    Happy Holidays!!

  15. Permalink  ⋅ Reply

    Santo Nucifora

    December 4, 2023 at 9:25pm

    Thank you for this information. I just got a Displayphone and had to create a power supply. I used a Meanwell RT-65B and your pinout above was invaluable. While mine had different chip numbers, it is the AA07. The battery has been removed and I am ready to try out the firmware with the enabled serial port. Thank you for providing the files as well.

  16. Permalink  ⋅ Reply


    December 30, 2023 at 7:32pm

    Managed to pick one of these up at an Estate Sale – neato! Power Supply has some bulged caps that need replacing, but it’s not clear what spec of caps it’s using, nor can I find a diagram anywhere.

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