4 Jan
2026
4 Jan
'26
6:03 a.m.
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
5 Jan
5 Jan
12:52 a.m.
Robert Jarratt via cctalk wrote:
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
I don't think that it where a bigger problem to change them against
similar powerful TO220 PNPs. The cooling isn't existent or only has a
small heat sink so that the allowed 40W power loss arent used anyways.
TO220 Transistors fit easyly on TO3 Footprints.
Regards,
Holm
--
Technik Service u. Handel Tiffe, www.tsht.de, Holm Tiffe,
Goethestrasse 15, 09569 Oederan, USt-Id: DE253710583
info(a)tsht.de Tel +49 37292 709778 Mobil: 0172 8790 741
3:01 a.m.
Hi Rob,
SANYO 2SD1239 PNP POWER TRANSISTOR TO3 D1239 | eBay
UK<https://www.ebay.co.uk/itm/226368697627?_skw=Sanyo+vintage+transistor+TO3&itmmeta=01KE6WR3HZV3HY85PX27W5MHM0&hash=item34b4a0351b:g:yNQAAOSwyr9m8r37&itmprp=enc%3AAQAKAAAA8FkggFvd1GGDu0w3yXCmi1e0NqieHkQKjfFYQrMIyqfI%2BQUGEHFe6IyHxeIkeFLA840R603xiOzLKAaa4GGd%2BbeQOKa2dkhZaPMd5%2FJA6lHWNnA8pHUcQZOSdAqvrNQX9CRwtzhCB8IXy5J95zKuhJ410eIQ1QFV5rPjaITQV4rerF%2FqdmTaqByFDfc%2Bur7By0TgkQUqfg5MrfzRqKRcvjuoZzKdBiDhpYan6E00MIQwzzliUhqsGSKVYU%2FV3kvbVy3dwo1JWl9zenZKUSLF%2BlrC7XDrbjmmx2bO5fO1tdBEiX0doTPOuSCvKVyGDT6yUw%3D%3D%7Ctkp%3ABFBMnLng3PFm>
FWIW, logo is Sanyo - these devices on ebay are marked in a very similar manner
Peter
________________________________
From: Holm Tiffe via cctalk <cctalk(a)classiccmp.org>
Sent: 05 January 2026 08:52
To: General Discussion: On-Topic and Off-Topic Posts <cctalk(a)classiccmp.org>
Cc: Holm Tiffe <holm(a)freibergnet.de>
Subject: [cctalk] Re: Identifying This Component from VT100 Monitor Board
Robert Jarratt via cctalk wrote:
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://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Frjarratt…
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://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbitsaver…atic_Feb82.pdf>.
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://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Falltrans…ansistor=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
I don't think that it where a bigger problem to change them against
similar powerful TO220 PNPs. The cooling isn't existent or only has a
small heat sink so that the allowed 40W power loss arent used anyways.
TO220 Transistors fit easyly on TO3 Footprints.
Regards,
Holm
--
Technik Service u. Handel Tiffe,
https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.tsht.…//www.tsht.de/>,
Holm Tiffe,
Goethestrasse 15, 09569 Oederan, USt-Id: DE253710583
info(a)tsht.de Tel +49 37292 709778 Mobil: 0172 8790 741
4:51 a.m.
Holm Tiffe via cctalk wrote:
Robert Jarratt via cctalk wrote:
An old friend of mine wrote me a mail, since his mails to cctalk seems
to go to nowhere andsuggested to forward (and translate) this
In the bitsaver schematic Q414 is a fat BU407 power transistor and must
be, since it has to resist high inductive voltage spikes, there for the
inverse diode.
He thinks that the transistor is a RCA411 and no 2SB ..it would fit
better there. Probably ore cheap would be a BU407 (reichelt.de 95 cent).
I would use an BU508D in TO247 / TOP3P housing, it contains the revere
diode.. but none of them is PNP...
Regards,
Holm
--
Technik Service u. Handel Tiffe, www.tsht.de, Holm Tiffe,
Goethestrasse 15, 09569 Oederan, USt-Id: DE253710583
info(a)tsht.de Tel +49 37292 709778 Mobil: 0172 8790 741
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
I don't think that it where a bigger problem to change them against
similar powerful TO220 PNPs. The cooling isn't existent or only has a
small heat sink so that the allowed 40W power loss arent used anyways.
TO220 Transistors fit easyly on TO3 Footprints.
Regards,
Holm
-- 
4:47 a.m.
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..
It seems a bit odd that the same component is labelled Q-something in one
instance and CR-something in another. Are the two TO-220 packages the
same component too?
Could someone have fitted the B411 component in the CR406 position in error?
This theory might be supported if the two TO-220 components on the other board
are not the same.
It also seems a bit odd that there seems to be a redundant mica washer under
CR406. Is there a missing heatsink? Is there even room for a heatsink?
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,
What do they measure? Are they a dead short or the same low resistance in both
directions or something else?
Bear in mind that some DMMs of recent vintage on diode settings might not be
expecting the lower forward voltage drop of a germanium diode compared to
a silicon diode.
Regards,
Peter Coghlan.
6:59 a.m.
-----Original Message-----
From: Peter Coghlan via cctalk <cctalk(a)classiccmp.org>
Sent: 05 January 2026 12:47
To: General Discussion: On-Topic and Off-Topic Posts
<cctalk(a)classiccmp.org>
Cc: Peter Coghlan <cctalk(a)beyondthepale.ie>
Subject: [cctalk] Re: Identifying This Component from VT100 Monitor Board
It seems a bit odd that the same component
is labelled Q-something in one
instance and CR-something in another. Are the two TO-220 packages the
same component too?
It isn't clear in the Mar82 schematic what the diode package is, it is
listed as optional.
Could someone have fitted the B411 component in the CR406 position in
error?
This theory might be supported if the two TO-220 components on the other
board are not the same.
From what I can tell, the emitter on the CR406 is not connected. So possibly
they used it as some kind of expedient.
It also seems a bit odd that there seems to be a redundant mica washer
under CR406. Is there a missing heatsink? Is there even room for a
heatsink?
What do they measure? Are they a dead short or the
same low resistance in
both directions or something else?
Using the diode function on the DMM I am measuring Q414 as follows
b-e forward voltage is 1.3V,
e-b reverse voltage is 0.15V
b-c is 2.7V (this is open on CR406)
c-b is 0.09V (and the DMM beeps for a short on Q414)
c-e is 1.4V
e-c is 0.17V
This assumes that the package is as shown on p54 of the Mar82 PDF.
For some reason I hadn't spotted that b-c is so different between the two. I
have always suspected Q414 is bad.
9:59 a.m.
It isn't clear in the Mar82 schematic what the diode package is, it is
listed as optional.
I somehow thought that you had another board with two TO-220 packages on
it or had seen a picture of one or something like that.
From what I can tell, the emitter on the CR406 is not connected. So possibly
they used it as some kind of expedient.
If there is a possibility that a previous owner has been fitting random
components in an attempt to get it to work, I'm inclined to agree with
Tony and Holm here and suggest the correct component to fit is a BU407(D)
or the BU508D suggested by Holm. It looks likely CR406 is supposed to be
a two terminal diode, not a TO-3 package and this component is not required
if the transistor at Q414 has an integral diode.
As Holm alluded to, the board could have been designed to accept
either TO-220 or a TO-3 packages in the Q414 position. Even if you
received it with a TO-3 package present in this position, this doesn't
mean it left the factory like that, especially if the solder joints
didn't look original. Its looking increasingly likely to me that the
B411 components do not belong there, whatever they are and I would
suggest forgetting about trying to figure out what they are and just
get rid of them.
I don't think it is in any way likely that some VT100s have a BU407 in
the Q414 position and others have a germanium PNP transistor in the
same position with the same component reference.
If you don't have another VT100 board to look at, maybe you could ask
someone else to look at theirs and see what is in the Q414 position?
I doubt the component varies significantly between VT100 versions unless
the board was changed really drastically and if that were the case,
the component reference numbers would have changed. (I don't have any VT100s)
Unfortunately, if you do fit a BU407 or a BU508D, the terminal might still
not work as whoever worked on it previously may have failed to identify
the original source of the failure.
Did the terminal ever work since you got it?
Regards,
Peter Coghlan.
11:54 a.m.
- 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.
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.
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?
12:39 p.m.
I have a VT100 externally dated May 1983.
Q414 on this unit is a BU407 (T0220 package) mounted on a small vertical heatsink, there
does not appear to be a CR406. Q310 appears to be a Motorola MJ3029
There are some TO3 packaged devices mounted on heatsinks - none of these have the captive
star washer style nuts shown in your images. None have mica washers
I agree with others that the unit may have been 'repaired' by someone without a
service manual.
It may be an entirely different circuit topology - the image that you included does show
Sanyo 2SB411 power devices
Are you able to trace the circuit through and give an idea of the topology?
Peter
12:46 p.m.
-----Original Message-----
From: Brent Hilpert via cctalk <cctalk(a)classiccmp.org>
Sent: 05 January 2026 19:54
To: General Discussion: On-Topic and Off-Topic Posts
<cctalk(a)classiccmp.org>
Cc: Brent Hilpert <bhilpert(a)shaw.ca>
Subject: [cctalk] Re: Identifying This Component from VT100 Monitor Board
- Were those measurements made in-circuit or out?
All measurements out of circuit.
- 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.
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.
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?
12:54 p.m.
-----Original Message-----
From: Brent Hilpert via cctalk <cctalk(a)classiccmp.org>
Sent: 05 January 2026 19:54
To: General Discussion: On-Topic and Off-Topic Posts
<cctalk(a)classiccmp.org>
Cc: Brent Hilpert <bhilpert(a)shaw.ca>
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.
6 Jan
6 Jan
12:15 a.m.
On 2026Jan 5,, at 12:54 PM, Rob Jarratt <robert.jarratt(a)ntlworld.com> wrote:
If the H output circuitry were as in the schematic and the “CR406” is NPN and the
collector on GND (as it appears to be and I think you mentioned) then it would be the
wrong orientation to be functioning as the CR406 in the schematic.
So I was looking for a way it might make sense for that C to be GND, thus the above.
Just speculation, we’ll see what your RE schematic shows.
-----Original
Message-----
From: Brent Hilpert via cctalk <cctalk(a)classiccmp.org>
Sent: 05 January 2026 19:54
To: General Discussion: On-Topic and Off-Topic Posts
<cctalk(a)classiccmp.org>
Cc: Brent Hilpert <bhilpert(a)shaw.ca>
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.
5
days inactive
7
days old
11 comments
6 participants
participants (6)
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Brent Hilpert -
Holm Tiffe -
Peter Brown -
Peter Coghlan -
Rob Jarratt -
Robert Jarratt