DEC terminals for New England Digital Synclavier II

The VT100 is, indeed a DEC terminal. It's very well-known and not too hard to fidn, but equally there are people who want them. You might also consider a VT101, which looks the same but has more limited intenral expansion (and an easier-to-fix PSU). I don;t think DEC ever made a VT640. The VT640 I know of was made by a company called soemthing like 'Retrographics'. It was a VT100 (genuine DEC) with an extra board added to give a graphics mode (I think the '640; in the mdoen mumber was the horizontal resolution). This board intercepted the RS232 lines between the host machine and the VT100 logic, DEC kidnly provided a connector for his purpose. For text-only operaiton the VT640 and VT100 are indentical AFAIK. FWIW, I think most later DEC ternminals (VT220, VT3xx, etc) will eessentially emulate a VT100. And just about any terminal emulator program offers VT100 emulation. Of coruse this doesn't help if you wanm the real thing. I'e never used a ADM-3A, so I can't comment o nthat one. VT100s were very common. I can see 2 from where I am sitting (and a VT105 too, which is a VT100 with a DEC graphics module). However, soem DEC enthusiasts also like to have the origianl type of terminal for their PDP11s and VAXen, so these terminals may or may not be easy to find now. The VT640 is not common. I've only ever seen one, that was some years aog. I didn't; get it, a friend and I were colelcting old DEC 'junk'. He got the VT640, I got a VT55 (complete tiwth the built-in electrolytic printer). I think I made the right choice.... As to faults : The VT100 logic is very reliable. There are 2 custom chips in the video ciruitry, but they tend not to fail (I dont think I've ever replacved one). The keyboard uses the same contact system as the VT52, TI99/4A, origianl TRS-80 Model 1, HP85, HP9816, etc. The keyboards can have contact trouble, but it's gernally fixable. The VT100 PSU is a switcher. It's a relatively friendly swithcer iwt hthe cotnrol circuitry o nyhe isolated side (powered by a little linear supply), but it still cah have problems. The VT101 has a simpler suppy lwith a big mains transformer which might be easier to repair The video monitor can have problems. Flyback transformers fail (and are non-trivial to get now). Diodes o nthe video board also fail, this cna kil lthe flyback transfoemer. The CRT can also lose emission, but do clean the screen ebfore thinking about relpalcign it (yes, I fell for that once). The genuine VT100 has a white phosphor IIRC, but the VT640 I say had a green phosphor CRT fitted. -tony