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Discussion Starter #1
I had a problem with my new (to me) D&H A-B-A Alco (20-2633-1). When going over a few switches at moderate speed, it would hesitate. At high speed, it wouldn’t hesitate, but the cab roof number light would blink off. Seemed odd that a diesel A-B-A with four widely spaced pick-ups would do that so I measured the resistance between the lead A unit and trailing A unit pick-ups. I was expecting 0 ohms, but was surprised to see 6.7 megohms. I also noticed that the lead pickup was sticking. I freed that up which solved the hesitation problem. But I have a few questions.

If the tethers don’t carry track power, what do they carry? I’m somewhat challenged electronically, but I’m guessing they carry logic signals to operate the trailing unit headlight, smoke unit, speed control and coupler.

Is it possible (for someone that is electronically challenged) to add a speaker to the trailing A unit? Each A unit has a board so I’m wondering if there is a connection on the trailing unit board to plug in a speaker for the trailing A unit.

What is the part number for the speaker? The MTH site has a parts list, but it’s for a 5V board. And it doesn’t give part numbers anyway.

Will the lead A unit run by itself? I’m guessing it will, but the manual is silent on this and I don’t want to risk it.

I attached a few shots of the boards. Cab # 17 is lead unit and cab # 19 is trailing unit.
548932

548933
 

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I have run the A powered unit from MTH F3 ABA sets by themselves before. They can operate this way I believe...

Tom
 

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GRG can explain adding an additional single wire tether to solve the switch issue. He's posted on this subject several times.
 

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Discussion Starter #4
Thanks Tom.

Mike – I solved the switch hesitation problem. It was just a stuck pickup on the lead A unit.

BTW, I also found out that I can’t run a speaker off the trailing unit slave board.
 

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Did you replace the original speaker in the sound unit with the aftermarket speaker you bought? How did that work out?
 

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Discussion Starter #6
Did you replace the original speaker in the sound unit with the aftermarket speaker you bought? How did that work out?
If you are talking about the 2-8-8-2 speaker, here is the thread.
 

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Sorry, I took a leap of faith - that you wanted more sound output by adding a speaker to the second A unit. And that may be accomplished by upgrading the speaker in the first A unit.
 

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Discussion Starter #8
I did want to add a speaker to the trailing A unit, but since there is no easy way to do it, it’s not going to happen. The hobby speakers I got for the 2-8-8-2 are way too big for the available space in the diesel. I don’t know if there is a better speaker that would fit in the available space, but I’m not inclined to try it.
 

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Discussion Starter #12
So, if I understand correctly, I would need the transmitter and receiver, buck boards (for the 5V power supply), a speaker for the slave unit and room in the master loco for the boards. The transmitter would get its audio input from the speaker in the master loco wired in parallel.

Sounds (no pun intended) pretty cool. Even cooler if there was also sound coming from the B unit. Don’t think I’m brave enough to do it myself though. If I decide to go that way, I would probably drop the locos off for my favorite ASC tech.
 

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Is there room for the hobby speaker on the B-Unit. You could also route a 2-wire tether from the A's sound board to the B-unit to drive it.
 

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Discussion Starter #14
The hobby speaker would fit inside the B shell, but not in the normal speaker housing which is under the chassis. I would have to drill holes in the chassis to let the sound out. But I’m not inclined to run another tether. I was just wondering if there was a place on the slave board in the trailing A unit for a plug and play speaker addition.
 
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