[John V.]

About 30 years ago I bought a used Autopulse Momentum 2.5 transformer to run my own trains as well as the various model trains that my 4 sons were given by my wife's aunt and uncle upon their birth. Likely saw an ad in the newspaper classifieds. I'm remember the Seller explained that he had repaired the transformer and perhaps even what he did to repair it. It worked and that's all I cared about at the time. It continues to work well today although it has gotten very limited use, I don't recall using it except at Christmas.

This Christmas I bought 2 of the same transformers off eBay with the intent of giving them to my son's so their own kids could operate their old trains. The 1st supposedly "powered up" and the "switches work", the 2nd was "good condition, never used" and it does look brand new. Since these transformers were made in the '80s before the Chicago based company went under, I knew it was a risky purchase.

Sadly, neither one seems to work. The 1st one seemed to run at full speed regardless of throttle (potentiometer) position. The 2nd had no voltage regardless of throttle position.

I only tested for a short time as I was afraid of damaging the engine.

I found a couple forums discussing the Autopulse transformer. Learned a lot about the history of the company that produced them and got some good insight, seems they were prone to blowing "power transistors" under warranty which apparently had a lot to do with putting them out of business. Remaining inventory was apparently liquidated at a midwest area model train show which may explain why so many of them are still being sold on eBay.

Part nos. for the transistors and the potentiometers that are suitable replacements were noted in one forum thread. Also suggested was adding a resistor in series between the pot and the power transistor to prevent frying the pot if the transistor were to fail.

I haven't opened them up yet (requires drilling out pop rivets to open the case (I guess they were afraid of kids opening them up if they used screws?).

I'm no electronics whiz so I'm not certain I would be successful attempting repairs. But it looks like repair parts are pretty cheap so I'm willing to take up the challenge. Wondering if anybody has had experience repairing an Autopulse Momentum 2.5 transformer that could offer any advice?

The forum thread that I found most useful is here:

https://www.therailwire.net/forum/in...?topic=41844.0

Covers a 2 Track version of the transformer without the Momentum and Brake switches that my single track units have but otherwise very similar in design.

BTW, before I purchased the two off eBay, I went to buy an MRC Tech 7 unit that appears to have the same features (Momentum and Brake) as the old Autopulse units. But nobody has them in stock, apparently the chip shortage has interrupted production of the Tech 7 at MRC. I know there are "better" controls on the market now but the Tech 7 was already more than I planned to spend so I wasn't about to spend over $200 for other available choices. I'm hoping I can get the Autopulse transformers working for under $50 each including what I've paid for what has proved to be "cores". With most of that already "sunk" cost, I figure it is worth a shot.

Any Autopulse transformer repair experts here?

[Stuckinda60s]

Not an Autopulse expert, by any means. But I did stay at a Holiday Inn Express last night. Humor aside, I do know some electronics and electricity. You've had your Autopulse for a long time, and I'm willing to bet that you never slammed the throttle wide open or tried to drag race two engines, right? The damage to the power transistors was probably a surge from actions like that. There'd be a pretty heavy surge that would be much heavier than what they were designed for. With reasonable use, I'd expect them to last like yours did.

As far as opening them up and repairing them? Go for it, they're not worth anything to you the way they are and it won't be that difficult. As for the one with no power, the power transistor should be apparent, they're pretty large for an electronic component, and shaped flat, silver color with printing on them and have a shape like an elongated baseball diamond with rounded ends. They're usually bolted into a socket and have three leads. You can find their front-to-back resistance values on-line and determine if they're bad. They don't cost much and you might find a similar unit with a higher capacity.

The one that only runs at full speed. I doubt that the pot is the problem. It's more likely that there's an electronic board with a bad component. You might be able to take the power transistor from that one and use it in the no power one.

I found this link to one being sold by a guy with 2665 100% positive feedbacks. The price is $15.00.

[John V.]

Thanks for chiming in RIch. I still haven't had time to open them up.

Never drag raced locomotives. And the "layouts" have been 4-5 ft. dia. circles or ovals in G scale. When I mentioned to a hobby train retailer that I was looking at the MRC Tech 7 he commented that it wouldn't be sufficient to run G scale. That may be true if I was running a very large layout with several pieces of rolling stock. Turns out the Tech 7 has about the same output as the Momentum 2.5 so I'm sure it would be just as suitable for what I'd use it for.

As far as other abuse, given that the trains have usually been operated by youngsters of the 2 yo thru 8 yo variety, not only has the throttle been slammed wide open at times (with or without disputes/fights over who is "in control" at that moment) but also the kids tend to hit the Direction switch with the train in motion despite repeated instruction from grandpa. Grabbing the locomotive while in motion also occurs on occasion. Derailments are pretty frequent. It is conceivable that my old transformer was made more robust when repaired. But likely, it just hasn't been over-stressed due to the small layout size, accounting for its longevity.

I've thought about opening it up to see if I can tell what components were replaced and perhaps just duplicating that repair. But I figure I should leave well enough alone and repair the latest acquisitions based on whatever I find inside.

I'll post again once I get around to opening them up.