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I have a MTH SD70MAC locomotive which (I think) has a bad chip. When power is applied, I get the 2 dings & the diesel sounds start, but that is all it will do (please see first video). When I try to do a reset, it makes the air release sound after the 1st voltage drop, but nothing after that until the power is cut off. You can hear the relays clicking (second video). The third video is the same engine, same card set, but with a chip from my PRR T1 steam loco installed. Everything works (sounds & movement) as normal. Since it works with the T1 chip and not the SD70 chip, My thoughts are the chip is bad.  Is there any way to get another chip for this engine?


Videos (3)
PS1 SD70 - Stuck
PS1 SD70 - Reset 18
PS1 - T1 chip
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Thank you immensely for posting the videos.  Not only are these helpful to analyzing your situation, but will also help with those of other folks who have a range of similar challenges with Protosound 1.

Your SD70MAC's chip is most likely not bad, just old.  The earliest Protosound units are very finicky with respect to startup and this locomotive appears to be one of them.  (What leads me to this conclusion is the fact that substituting the chip from a later Protosound 1 model, your T1, solves the problem.)

The sequence you must follow to get a good startup is much more precise with the earliest models.  This includes not only positioning of the throttle, and its movement, but the model of the transformer you use.

Follow this link for more detail, embedded within a previous poster's related question on Protosound 1:

   Rock island set MT-2127LP | Merlin

Be aware that there is also an alternative approach, which for whatever reason is quite different, that was published back in the day, apparently by MTH.  See this link:

   PS1 Cautionary Note | mort1345

Good luck, and let us know how things turn out.


Last edited by Mellow Hudson Mike

Here's the list of affected locomotives.

---Click on graphic to enlarge---

MTH ProtoSound Deselect Problem Engines

Hello John,

I own a few PS1 engines that is shown on this list.  Presently the engines run just fine as I've been careful with them.

What is your recommendation concerning engines found on this list?  Should they be upgraded and if so to what?

What would be the lowest cost option of the recommendation's?


@John1361 posted:

Thank you everyone, for the replies. Unfortunately, following the above procedures did not make any difference. The loco just sits there making engine sounds. I did see that a new MTH parts website will be online soon. I gusee I'll be looking for a replacement chip for this engine.


There's one last method to try.  I alluded to it earlier but didn't provide any details.  You'll find them in this note, which was apparently published by MTH very early on.  It seems to contradict the methods that work for most of us and sometimes the contradiction is quite significant.

I think this is because it applies only to the very earliest PS1 systems.  Yours may be one of these.

Give it a try.

Thanks to @mort1345 providing this document in the thread I reference earlier called PS1 Cautionary Note | mort1345.

And good luck with your chip replacement if it comes to that.


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