> -----Original Message-----
> From: Brent Hilpert via cctalk <[email protected]>
> Sent: 05 January 2026 19:54
> To: General Discussion: On-Topic and Off-Topic Posts
<[email protected]>
> Cc: Brent Hilpert <[email protected]>
> Subject: [cctalk] Re: Identifying This Component from VT100 Monitor Board
>
> - Were those measurements made in-circuit or out?
>
> - The photo-board has the same component IDs as the Mar82-board
> schematic.
> However the photo-board layout differs from the Mar82-board layout.
> So, for as much as can be discerned from the photo, it appears or suggests
> they did make two board layouts for the same circuit.
>
Yes a lot of the part labels and values are the same, but there are
differences. I am gradually reverse engineering a schematic in KiCad.
> What could make some sense for the photo-board is if they were using one
of
> the B411s as a fast non-saturating clamp diode - actually wired and
intended
> to function as CR406.
That is indeed how it is being used. The emitter is not connected to
anything.
>
> In which case you would expect:
> CR406.C == GND (A)
> CR406.B == GND (A)
> CR406.E == Q414.C (K)
>
> This would explain why (one of) the collectors is connected to GND.
> This would want a high BE reverse breakdown V though.
>
> Might there be a BC connection underneath the transistor on the component
> side?
Not sure what you mean by this.
