I have a 15 year old Bachman Big Hauler, number 177 that has served me very well until 6 months ago. The motor died so in August, I ordered a new Chassis, 40007. I recently tore into my Bumble Bee to swap the old chassis for the new chassis. This was a fairly easy process until I discovered some of the mounting posts inside of the body broke up while removing the screws. I tried to reattach the remaining posts with super glue but none of these would hold up when I inserted the body screws so I decided to order a replacement body also from Bachman. The only body available in the Bumble Bee scheme was a 4-6-0 Anniversary body so I ordered that. Knowing that I was going to have to rewire the headlamp to make it an LED and since my old smoke unit was bad also, this seemed to be my best option. When the new body arrived, I got back to work on my rebuild. I realized that the new circuit board for the new chassis had what appeared to be JST connectors for the various inputs & outputs so I had a few sizes of JST's lying around and I had to order a few new ones to make sure I had enough connectors. The number on this circuit board is G912X-PCB06-A. So my question to Bachman is, do you have either a wireless no diagram or a schematic of this board that I can print out? If not, I need some guidance on each of the four JST connectors located in the middle of this board. I assume that the 2 pin connector on the far left,labeled as SMK+ goes directly to the new Smoke Unit. The second from the left is a 4 pin connector labeled SWITCH/LED and the third from the left is a 3 pin connector labeled as Sensor. I can't figure out where these two connectors go. The last is a 2 pin connector which is on the far right edge of the board is labeled as Trigger. Can I assume that connector goes to the Tender connector for the Chuff Trigger?
I appreciate your help and support with these questions! Thank you,Steve Johnson
There is a thread on MLS about this.
So, no one has a schematic
I believe the board is designed to accomodate old and new wiring schemes, specifically chuff triggers.
One version is a simple switch, that is most likely the 2 pin connector.
The other style uses a sensor, which takes 3 leads...
That's our best guess.
Thank you for your response! From earlier searches, I assumed that no schematic available was probably the answer. I also assumed based upon many years of electronics experience that the two and three pin connectors were exactly as you described. I just wanted a better explanation if possible from the factory. So I'm assuming that on my older model, the three pin connector does absolutely nothing then? If this is true, then you've granted my every wish and I truly thank you, sir!
older model was mechanical switch, drum with contacts on axle. two wires. I'm not sure when/if the latest version has the ir sensor... I know the C19 has a blade inside the cylinder connected to the piston rod that is the trigger. Again, have not seen it apart, but I think it might be a led on one side and the sensor (+, -, trigger) on the other side.
hmm... looking at the C19 wiring diagram, the sensor has 4 wires...
Maybe someone knows, but does your chassis have the chuff "drum" on one of the axles?
So the latest Bachmann "Standard" (non-Anniversary chassis) (it's not v7 or v5, what are we calling it?), has connectorized assembly as as you noted and in the "chassis" there is a central PCB (G912X-PCB06-A) that accepts all the connectors:
Track, 2-pin connected to wires from base plate containing wheels and pilot truck pickups (so this is power in)
Motor, 2-pin connected to motor, note polarity noted as M+
Smoker, 2-pin connected to smoke unit in "shell"
SW/LED, 4-pin connected to headlight LED in shell and "most likely" to Smoke On/Off Switch under smokebox door. Two functions, LED power and Smoke On/Off.
SENSOR, 3-pins going to the new chuff sensor on the front driver axle (PCB08). Looks to be optical/IR with a two-blade interrupter plate on front driver axle.
The 3 pins are VDD (a voltage to the sensor created from track power using a DC/DC converter (see U2), GND, and 'T' which is basically the signal from
the sensor.
This optical sensor signal needs to be converted to something the tender can use just like what was created by the chuff drum and contacts in V5 and below.
This is done by Q1 and the 4-pin device next to it, an opto-coupler whose output transistor is connected to the TRIGGER connector. So a transistor replaces
the chuff mechanical contacts.
TRIGGER, 2-pin connector that connects to the small pcb at rear of loco (PCB02) that contains the chuff on/off switch and the two-pin connection to the
tender to "trigger" the chuff sound board in tender.
So if your chassis still has the chuff drum and pickups on the front driver axle, these two wires to go the rear loco PCB board (PCB02).
If your chassis has the newer front driver AND the sensor board, the sensor board (PCB08) is connected to SENSOR and the TRIGGER is connected to the rear loco PCB (PCB02).
New V? PCB (G912X-PCB06-A)
https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=69_671_148&products_id=14587
New front driver chuff sensor (PCB08)
https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=69_671_148&products_id=14586
New front driver (notice interrupter plates in center of axle)
https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=69_671_148&products_id=10420
Rear Loco PCB (PCB02) supply connection point to tender cable
https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=69_671_148&products_id=10232
My new chassis (40007) does not have the Chuff Drum on either of the axles. I do have an additional question. I know that the wheels on the pilot truck have electrical power pickups but I also thought that at least one set of the main driven wheels also have power pickups. If this is true, then my new chassis is not working correctly. I have not disassembled the cover on the bottom of the chassis yet but I did set up the chassis on a set of 4 test rollers, all electrically connected but when I slid a piece of paper under the pilot wheels, my chassis stopped rolling. When I remove the paper, the chassis runs which means to me that the driven wheel pickups aren't working. I'll remove the bottom chassis cover tomorrow to investigate but I'm fairly sure that something is amiss!
The chuff drum OR chuff sensor will be on the front driver. Should have one or the other.
The bottom cover (known as Loco Underframe (Large 4-6-0), 900XX-UF-01) contains two long brass strips, left and right that contact the front and rear drivers (the middle is a dummy driver). On a fully assembled underframe (V5B but not V5), the pilot truck wires connect to the brass pickups and then a single pair of wires (track power) go up an into the "chassis".
Underframe
https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=69_671_148&products_id=14592
Brass Pickups (Contacts/Pair Anniversary(Large 4-6-0), G812X-MT010
https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=69_671_148&products_id=8854
Quote from: wraujr on November 12, 2025, 08:15:17 AMcontains two long brass strips, left and right
The older models had the strips connected to the chassis with a push-in plug, so that you could completely remove the bottom plate.
Maybe one of yours is loose?
The latest chassis would not have the drum or the long brass strips because the new electronics uses an optical sensor. on some of my older chassis chuff was spotty, and when I opened them up I found that crud on the drum was preventing good contact. A good cleaning took care of the problem. The optical sensor should be much more reliable.