[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?