[cctalk] Re: Identifying This Component from VT100 Monitor Board

So many great replies here, thank you to all. I will try to answer everything in one place. First of all, the terminal has never fully worked since I have had it. Initially I couldn't even get a sensible display using the external video connector, but I have since repaired the Basic Video board and now it works on the external video connector. As requested, I have taken additional pictures of the board. Pictures here: https://rjarratt.wordpress.com/wp-content/uploads/2026/02/img_20260202_2243… Note that I replaced some of the electrolytics (I know Tony doesn't agree with this and perhaps I should have waited before doing this). Also, some of the components are partially lifted to assist with diagnosis, this was a while ago when Tony gave me a few suggestions. Finally, one of the yoke wires (brown) is also broken now, I am not sure when this happened. I am sure it wasn't broken originally and it may have failed during all my probing and checking for the schematic. However, I believe it drives the heater and this may explain why I could never get a glow from the neck of the tube. Peter asked a number of questions: - The body of Q414 is connected to HORIZ GND. No signs of modification that I can see, but I have desoldered it now and I guess any evidence may have gone. I have taken pictures of the area now as above. - Certainly the printset shows Q414 as NPN. I am not sure if this "B411" is really PNP or not. I cannot get sensible measurements with the DMM diode tester out of either of the two. Although the one in the Q414 position does show open circuit on the B-C junction when I apply a positive voltage B-C and 0.1V when I reverse the probes. This at least would suggest it is PNP. - I cannot see how a BU407D could have been fitted here without it looking very odd, the footprint on the board is definitely TO3. I haven't got around to thinking how I might install a BU407D, although I have bought three now ready to try if needed. - Regarding the remarks about the CR406 and the mica washer. The footprint is definitely TO3 as you should be able to see in the photos, were there TO3 diodes? - Yes you are right, I did mean B411 and not BU411! Sorry just getting confused. To answer Tony's questions: - You are right, J3 is the BASE, I confused the terminology and I will correct the schematic. - You are also right about Q101, I got it connected the wrong way round, again corrected. New partial schematic here: https://rjarratt.wordpress.com/wp-content/uploads/2026/02/5414131-partial-s… Full KiCad project here: https://github.com/rjarratt/Schematics/tree/main/VT100 So many of these questions would be answered if there was another one of these boards to compare against. Someone must have the same board somewhere