# Converting old Atlas engine, need help



## tkruger (Jan 18, 2009)

I have converted several Athearn BB. This is my first try at an Atlas. This is the older model of the GP 38-2. 

My question is this. The frame does not get power from the trucks. It is metal and the metal motor is mounted to the frame. Thus the motor is not isolated from the frame but is from the track power. Is this a potential issue? It is held on by a single metal screw. 

For DC there is a board on top that has a piece of spring steel that contacts the upper brush. A screw goes through this board to contact the motor frame, This is what the other brush is connected to, and why the frame received current from the bottom of the motor.

Below is a shot of the loco in question:


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## mopac (Feb 24, 2011)

I have only done BBs as well, but here is what I would do. Time for the board to
go. Decoder motor wires need to be soldered to the brushes. I see the wires from 
the trucks so maybe the frame is not powered. Check again after removing the
board and if no power to frame you are good to go.


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## Cycleops (Dec 6, 2014)

This looks very similar to an old Atlas I have, an S2 made by Roco. The pick up for the bottom of the motor is connected electrically and physically by a screw which holds the motor. This needs to be eliminated and replaced by a non metal screw (Kadee offer one) and the motor bottom covered in Kapton tape where it contacts the frame. The weight also needs isolating by the same method. Solder wires directly to the motor after cutting down the brass contacts. Replace the bulbs with leds. The board with the bulbs can now go.

This installation on the TCS site shows it better than my explanation! http://www.tcsdcc.com/Customer_Content/Installation_Pictures/HO_Scale/Atlas/S2/Atlas S2.htm


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## DonR (Oct 18, 2012)

Tkruger

Just to clarify. You say that the frame is isolated from
the track power, and that the motor is mechanically 
attached to the frame. The motor tabs do not touch
the frame.

If that is correct, then the motor in contact with the
frame would be safe. Before you 'fire up' the decoder,
you should do a final test, multi on ohms, probe on
either motor tab, other probe on frame. If zero good.
Do the other motor tab If zero also you're home free.

Just make certain the light wiring does not touch the
frame.

Don


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## Cycleops (Dec 6, 2014)

No, that's not correct Don. The frame of the motor is 'live', the contacts touch the frame, That's why you need to use the Kadee screw for fixing it and put Kapton between it and the frame, then the motor is isolated and the motor contacts can go straight to the decoder. Its difficult to visualize without having it in front of you. Have a look at the TCS pics again.


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## tkruger (Jan 18, 2009)

Thanks for the information. This is a locomotive that I purchased for $5 from a junk box at a show. Have a NOS Digitrax sound decoder for $35 from EBay. With a little cosmetic work I should end up with a decent locomotive. Not sure if I will use this shell or look for a different road-name yet.


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## DonR (Oct 18, 2012)

Cycleops

What you describe sounds like the split frame, no wires Bachmann
loco I converted to DCC. The two sides are isolated from each
other and the motor tabs are held against the sides for power.

That doesn't appear to be what tk has. He says the track power
does not go to the frame and his pic shows the wires running along
the top. If neither motor tab actually touches the frame, and if
the motor shell is not hot by either motor tab, then he should
be OK with the metal screw to the frame and no need to insulate it.

Don


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## Cycleops (Dec 6, 2014)

I'll try to post some pics of my old Atlas so you can see more clearly.


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## tkruger (Jan 18, 2009)

The link from Cycleops' earlier post is exactly what I have only shorter. Thanks.


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## DonR (Oct 18, 2012)

Cycleops

I sure don't want you to think I'm arguing with you because I am
aware you have the loco, or one similar, so I definitely defer
to your actual experience. This is a learning experience
for me. But I'm trying to understand
what seems excessive 'insulation' of the frame. Maybe I'm not seeing
the wipers and what and how they are attached to the trucks which
could make a big difference. Since there are wires from the wipers
they are not using the friction contact from the wipers to a split
frame, so I'm having difficulty understanding how there is track contact
to the frame. (I am basing the above after studying the link you provided,
especially, the 'update' version.)

Don


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## tkruger (Jan 18, 2009)

DonR said:


> Cycleops
> 
> I sure don't want you to think I'm arguing with you because I am
> aware you have the loco, or one similar, so I definitely defer
> ...


The top circuit board is held to the motor by a screw that bolts it to the frame of the motor. The metal frame of the motor is permanently attached to the lower contact that goes to the brush. Now the metal motor frame also sits directly on the metal chassis thus connecting it to the track power via this circuit. For this reason we have to use tape to stop the motor from touching the frame. Since there is a metal screw going from the frame to the motor housing that must be replaced with a non-conductive one also. 

If the frame is allowed to have current an a derail happens it could cause the tank to hit the tracks and send the wrong current to the decoder down the wrong path. This would have bad results. This is my understanding.


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## DonR (Oct 18, 2012)

Aha

Now I understand. The frame is isolated from the track, but must
be isolated from the motor to avoid possible short by fuel tank
when derailed. 

Appreciate it.

Don


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## gator do 65 (Jan 27, 2014)

Cycleops & tkruger,
I would also like to thank you for clearing that up, I was thinking like DonR was! Learn something new everyday!


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## Cycleops (Dec 6, 2014)

gator do 65 said:


> Cycleops & tkruger,
> I would also like to thank you for clearing that up, I was thinking like DonR was! Learn something new everyday!


I think I may have misled you about the chassis wiring but tkruger has corrected that, thank you. I have some photos that make it clear but cant upload them currently. The bottom contact on the motor presses directly on the frame and the top contact is isolated from the motor chassis and contacts the light board on top.


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## DonR (Oct 18, 2012)

I have two Bachmann GP30s, the newer one uses standard
solid cast frame, wheel wipers, wires to the decoder then
wires to motor and lights. The older, however originally
had ZERO WIRES. It has a split cast metal frame, springs
attached to wheel wipers transfer power to each side of the
frame. The motor has tabs pressed against the two sides,
the light board has tabs pressing down on the sides, thus
power to everything and no wires for the makers to solder.
Clever design, and it worked.

Don


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