I asked this before a few years ago but didn't come to a firm conclusion. The two parts are shown in this picture: https://rjarratt.wordpress.com/wp-content/uploads/2023/12/img_20231221_1123…
They are from a VT100 Monitor board. There is no schematic for my version of the board, but a related schematic is on p58 of this schematic: https://bitsavers.org/pdf/dec/terminal/vt100/MP00633_VT100_Schematic_Feb82.…. They are labelled Q414 and CR406, but the Feb 82 revision uses a different board and those two parts are in TO-220 packages rather than TO-3 as here..
I have removed both of them and tested them with a DMM. Neither of them measure as two diodes, they do not measure open circuit in any direction, so either they are both faulty or they are not transistors (unlikely). I have found a spec for a 2SB411 at https://alltransistors.com/transistor.php?transistor=10279. This seems to be a germanium transistor. When I last asked about this I had a conversation with Tony Duell, who was very sceptical that these could be germanium transistors, so naturally I am very doubtful that they are 2SB411 transistors. However, in the schematic Q414 is shown as NPN, the 2SB411 is PNP and this seems to match the way the part is connected on my board (Collector to HORIZ GND). I am working on a reverse engineered schematic.
Can anyone tell me what these components are so I can find a datasheet for them? Better still a suggested replacement would be really helpful, especially if they are 2SB411s because they seem to be hard to find.
Thanks
Rob
