well?

Well I actually was able to use the board after watching the YouTube video at the top of this post and connecting the wiring for the chassis as he did.
No connections for smoke box, but was able to get the chuff sounds working using the tender connection using this method.

Here is a photo with wires connected. This allowed me to test the new chassis as received from Bachmann without cutting any wires
so I could confirm it was working when received. You cannot view this attachment.

To get back to the question - I still don't have thw two wires hooked up for the smoker on the original cab. I suspect that this should be connected to the left SMK+ connector, likely with the red wire to the right. I was rather surprised that there wasn't at least a sheet
of documentation for that board since it is likely to be used to retrofit older trains.
Also would be nice to know where sort of connector is used on the board, and sources for the wire ends connectors that match (and a likely source for same such as Mouser or Digikey or Newark).

This is a very valuable source for chassis change The pcb board detail photo shows the process to be very straight forward.  Looking at the board I see the smoke connection, but there are other potential connections that could be usefull as well.  I am in a middle of a move to a new smaller home and have no access to my trains or the chassis which I keep in stock.  By all means forum members seek out the other possibilities for using this PCB.  It will be a valuable contribution tho this board, and thanks to all so far.  Keep on exploring for those of us that will benefit from your contributions.

Cheers and Beers  Loco Bill

so, I see a 3 pin connector for "sensor" which I assume it the 3 terminal optical sensor, and then I see 2 wires to "trigger" which would seem perhaps the original metal make and break contacts.

so where do these 2 sets of wires go in your installation?

I am a novice at hobby trains, but electrically knowledgable. This is the hookup on a bare chassis purchased as a replacement from
Bachmann a couple of months ago, which was sold with zero documentation of the PCB provided (or even installation information of same
with the chassis). The 4 cables were the only wiring on the new chassis, and I connected them up by following video on the first comment on this thread. There is no old generation parts on this - it was hooked up to test the new chassis prior to putting the old cab on top
of the replacement chassis. The only part moved over is the weight from the old chassis.

I need to call Bachmann directly I suspose and see if I can get any additional information. I am not seeing anything on their website
that documents this board.

https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=69_671_669&products_id=4094 is the chassis I purchased for
reference to replace one on a 90037 locomotive, for reference.

Looking at the PCB, I would expect the two wires labeled "Trigger" to go the the rear of the loco where the small PCB with on/off switch provides the connection to the "chuff sound board" in the tender. More appropriate name might be "Trigger Out".  I can tell from the PCB that the chuff sensor (connector is 3-pin) is using some form of optical or hall-effect sensor. The circuity above the connecter is a DC/DC power supply needed to power (VDD) the optical sensor. In addition, near the Trigger connector is a Q1 and square 4-pin device that is probably a solid state relay mimicking the open/close contacts of the old chuff sensor. Since he has the new chassis the chuff sensor should be in place with the 3-wire connector attached.  He then needs to connector Trigger to the locos rear "Sound" connector board.  At this point, I don't beleive polarity matters.

seem the board can accept BOTH the old style make-break mechanical chuff contacts, AND the newer optical sensor unit

My question on post #20 was to determine what the heck was connected, it makes no sense to have BOTH of the "triggers".

Yes, if you look at the 4 pin device, it uses a transistor Q1 to connect to the 3 wire optical sensor electronics.

But I see no electronics relating to the sound unit/speaker...

perhaps this board was designed as a universal interface to new and old style electronics...

Since this post was from back in September, you may have already found your answer on the connector types for this board but in case no one else has responded yet, these are called JST Connctors. This stands for Japan Solderless Terminals. If you have the patience to search for them, you can go to one of the huge Electronic stores such as Mouser or Newark among others. I had some on hand from another project from several years ago but the tricky part here is that Bachman uses several different sizes of JST's along with different quantity of pins on these. I went to Amazon and after measuring the spread between each pin with digital micrometers, I ordered sets of each size to have on hand for future projects. There are so many sizes to choose from but Amazon has sets of each size relatively inexpensive. You can buy anywhere from 1.5 mm to 2.54 mm and any2here in between.

Quote from: deritchie on September 23, 2025, 06:31:45 PMTo get back to the question - I still don't have thw two wires hooked up for the smoker on the original cab. I suspect that this should be connected to the left SMK+ connector, likely with the red wire to the right. I was rather surprised that there wasn't at least a sheet
of documentation for that board since it is likely to be used to retrofit older trains.
Also would be nice to know where sort of connector is used on the board, and sources for the wire ends connectors that match (and a likely source for same such as Mouser or Digikey or Newark).

Quote from: deritchie on September 23, 2025, 06:31:45 PMTo get back to the question - I still don't have thw two wires

Quote from: deritchie on September 23, 2025, 06:31:45 PMTo get back to the question - I still don't have thw two wires hooked up for the smoker on the original cab. I suspect that this should be connected to the left SMK+ connector, likely with the red wire to the right. I was rather surprised that there wasn't at least a sheet
of documentation for that board since it is likely to be used to retrofit older trains.
Also would be nice to know where sort of connector is used on the board, and sources for the wire ends connectors that match (and a likely source for same such as Mouser or Digikey or Newark).

hooked up for the smoker on the original cab. I suspect that this should be connected to the left SMK+ connector, likely with the red wire to the right. I was rather surprised that there wasn't at least a sheet
of documentation for that board since it is likely to be used to retrofit older trains.
Also would be nice to know where sort of connector is used on the board, and sources for the wire ends connectors that match (and a likely source for same such as Mouser or Digikey or Newark).