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:
- The regular Displayphone (model NT6K00)
- The upgraded Displayphone Plus (model NT6K90)
- Displayphone user guide at the bottom of the page on Dave Dunfield’s site.
- Thread on classicrotaryphones.com with a link to a scanned manual.
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.
- 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.
- 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
- 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.
- 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:
- Press SERVICES.
- Press zero on dial pad.
- 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:
- Press SERVICES.
- Press zero on dial pad.
- 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.