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 &lt;cctalk(a)classiccmp.org&gt; Sent: 05 January 2026 08:52 To: General Discussion: On-Topic and Off-Topic Posts &lt;cctalk(a)classiccmp.org&gt; Cc: Holm Tiffe &lt;holm(a)freibergnet.de&gt; Subject: [cctalk] Re: Identifying This Component from VT100 Monitor Board Robert Jarratt via cctalk wrote: 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

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. 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.

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

&lt;cctalk(a)classiccmp.org&gt; 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. of intended That is indeed how it is being used. The emitter is not connected to anything. Not sure what you mean by this.

I have finished partially reverse engineering the schematic for the monitor board in my VT100. I have tried to make it follow the layout used in the printset. I hope I haven't made any mistakes, but it is quite possible that I have. As a reminder the Feb 82 printset (https://bitsavers.org/pdf/dec/terminal/vt100/MP00633_VT100_Schematic_Feb82.… on p58 of the PDF) has a schematic for this board. My board seems to follow mostly the same schematic (including part labels, values etc), but my board differs in some substantial ways. Q414 in particular seems to be a BU411 and nothing like the BU407D in the schematic, but I also have CR406 installed on my board, which the printset shows as optional, presumably because a BU407D includes the diode. The other big difference is the absence of the 555 (E1 in the schematic) that drives Q413. I have not reverse engineered the lower half of the schematic because the problem is to determine whether Q414 as installed on my board is correct or not. I have obtained a BU407D which I could now install at Q414 (although quite how I make it fit I am not really sure) The schematic is drawn in KiCad 9 and is here: https://rjarratt.wordpress.com/wp-content/uploads/2026/02/vt100.zip A PDF of the schematic I drew is here: https://rjarratt.wordpress.com/wp-content/uploads/2026/02/5414131-partial-s… This is a picture of the board https://rjarratt.wordpress.com/wp-content/uploads/2023/12/img_20231221_1122… Q414 is the TO3 on the heatsink at the left edge of the board with the marking "B411". CR406 is the other TO3 just above it without the heatsink. Would appreciate advice on whether to replace Q414 and CR406 with a BU407D or something else? Thanks Rob

Has the terminal ever been seen working in its present state? Is the body of Q414 connected to HORIZ GND or is it one of the pins of Q414 is connected to HORIZ GND? Is there any evidence of modification by a previous owner here? Is there any evidence that pin 4 (or pin 3 even) of T403 could have been originally connected to HORIZ GND and was modified by the same previous owner? Could it be that Q414 was originally an NPN silicon transistor but a previous owner modified the terminal in order to replace Q414 with a quite different transistor they had available to replace a possibly failed NPN Si transistor they didn't have and couldn't get, more in hope than conviction? If an NPN Si transistor like the BU407D was fitted in the Q414 position, can you see a plausable way that its emitter could have originally been connected to HORIZ GND and its collector (tab / body) could have been connected to the horizontal output transformer? I mean for example with the outer two leads going through the holes in the heatsink and PCB and soldered to the underside of the PCB and a bolt through the tab, the heatsink and one of the remaining holes in the PCB that presently have the mounting bolts for the B411 there? As drawn, the schematic suggests that there would be a relatively high voltage peaks between the primary and secondary of T403. I think it is less likely the manufacturer would have laid out the ciruit this way. If they were designing a circuit from scratch to use a PNP transistor, I think they would have connected the emitter of the horizontal output transistor to the positive supply and connected the horizontal output transformer primary between the collector of the transistor and HORIZ GND. This would allow a bit less voltage stress on T403 and allow a less highly specified part to be used in this position. Or possibly they could have laid out the circuit completely differently using a negative supply rail instead of a positive one. I find it hard to imagine the manufacturers using a transistor identical to the horizontal output transistor as a clamp diode in the CR406 position. I am similarly suspicious of the apparantly redundant mica washer under CR406. This seems more like the work of an enthusiastic amateur who had several of these B411 parts on hand (which we are still not sure of the identity of). I think the manufacturer would have been more likely to use a diode designed specifically for the application in the CR406 position. This is likely to be cheaper than employing only part of a second relatively hi-spec and likely expensive horizontal output transistor. If the B-E junction of Q414 as drawn is forward biased, I think C443 would end up with a small negative voltage across it and probably ought to be the other way around if T403 is connected as shown and Q414 is a PNP transistor and the supply rail feeding the horizontal output transistor is a positive one. Unfortunately, I don't have any suggestions for a replacement part to use. If my speculation above is correct, a BU407D might be suitable with its emitter connected to HORIZ GND and its collector connected to the horizontal output transformer and C438 and not to T403. Pin 4 of T403 would need to be moved to HORIZ GND. This ought to leave C443 with the correct orientation. However, if the manufacturer didn't originally use a BU407D, the specification of the horizontal output transformer may be different to that needed for a BU407D unfortunately. If the terminal has never worked and you have a BU407D on hand, I guess there is not much to lose in trying it, with the above changes also made. If the original transistor really was a germanium PNP power switching transistor, I imagine replacements are rare and expensive if obtainable at all, even if we can be sure of the correct identity of it. As far as I can see, the BU407D has an integral clamp diode and shouldn't need an external one so you should be able to leave the CR406 position empty. (I am not sure where BU411 came from, I think maybe you meant to say B411?) Regards, Peter Coghlan

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

Can you post to OneDrive or Dropbox maybe? Anyway it looks like it really is a Ge part. Thanks Rob On 4 February 2026 08:39:08 GMT, Harten via cctalk &lt;cctalk(a)classiccmp.org&gt; wrote:

Good idea. They are here as original KiCad files only: https://github.com/rjarratt/Schematics <http://tinyurl.com/d3d-pipeline>

On Sun, 1 Feb 2026, Rob Jarratt wrote: Looking at your photos, it seems that the schematic for the Elston DM10 could be the right one. It can be found on bitsavers in the Microterm MIME-I terminal manual. It really uses a PNP HOT as Q414. Christian

Flybacks do have a tendency to burn out on vt100’s. Since replacements are unobtainable, your terminal essentially becomes a parts machine. So check it out throughly. Sent from my iPhone

I hope to get back to looking at my VT100 either today or next weekend. My worry is the flyback, either that it is bad or that a problem on the monitor board might damage it. I could do a ringing test on the flyback and of course I need to check the "new" germanium transistors to make sure they are OK. However, I have a VT101 and a VT102, one of them at least uses the same Elston monitor and a different monitor board (not with Germanium transistors). I could temporarily swap the monitor board to see if the flyback on the VT100 is still good.But, I am worried about damaging a perfectly good monitor board. If the flyback is shorted, could I damage the good monitor board? Thanks Rob

Ok, thanks for the advice. I will take it slowly. Rob