I post this information in the hopes that anyone who has limited experience with transformers, and who owns an MRC AH501 that has ceased to work, might be able to fix the problem!
I recently purchased a used MRC AH501 transformer on eBay for use on my test track set-up. While testing my late uncle’s Lionel Pennsy #681, the track side of the transformer died, while the accessory side still had power.
There was also no direction, horn or bell operation.
Everything I had read On line said it was a “sealed” transformer with no owner serviceable parts. After continued reading, apparently other people had had other issues other MRC transformers, but had difficulty in taking the transformer apart due to the slotted “security” screws that held the two part shell in place. It turns out that that issue can be overcome by either buying a security screwdriver or cutting a small notch in the center of tip of a long straight blade screw driver with a Dremel tool or hack saw, and then removing the security screws.
Upon examination of my transformer, I discovered that someone apparently had already gotten into the inside the shell, as the security screws had been replaced by Phillips head screws which made taking the shell apart easy.
Now, the problem was, where was the problem?
I am not an electrical wizard by any measure, and I know enough about electrical equipment just to be dangerous. So I used a multimeter to see if I had power just inside the shell...which I did.
All I saw inside was a circuit board with a lot of what appeared to be capacitors and two stamped sized chips fastened to a circuit board directly beneath the horn, bell and direction buttons and a VERY large potentiometer!
I had NO idea where to begin trouble shooting.
I continued my research on line but found NO additional information and had read where MRC no longer did repairs.
I did however, find a tech support number for MRC in Matawan, New Jersey.
I called the number and spoke with a tech support gentleman named John.
I informed him that I had just purchased an MRC AH501 that had appeared to be practically brand new but had failed. The first question he asked was, had I reset the circuit breaker button on the outside of the case near the on/off switch...I said there was no circuit breaker.
He replied, “Oh, that is a very old AH501 that was discontinued in 2006! Unfortunately there are no replacement parts available.” I then asked him if he knew of any problems with this transformer that I might be able to repair, and he said, “Well there are three possible places where there have been problems...two of which you might be able to fix, and the third, well, it is not owner repairable!”
So I asked him to talk me through the two possible repairs!
He said the first is easy. There is a fuse holder that comes apart (threaded) and check the fuse...if it burned out, that’s an easy fix. If it is good, then the next possibly problem source is on the underside of the circuit board. The circuit board is directly beneath those three buttons for the horn, bell and direction.
Carefully unscrew the board, turn it over, remove the Yellow plastic bar and you will see three copper “traces” (thin copper sheet metal about 1/2-5/8” long and 3/8” wide) that are soldered at one end to the circuit board. After 14 years of continued use, those solder points become brittle and crack or separate and that will short circuit and cause loss of track side power. He asked me if I was good a small part soldering and I told him I was fair.
I thanked him for his help and told him I’d give it a shot.
I checked the fuse and it was good.
That meant removing the circuit board...which I did, and found that one of the traces was broken off at the solder point, and another was cracked. The solder at these junctions was extremely thin and oxidized.
I don’t know who designed this setup, but I think regular push button switches would have been a far better solution...probably a cost cutting measure.
Well, I didn’t have a fine point soldering iron, just an electric soldering gun, I so I decided to give it a shot VERY carefully. Given the age of the unit, I decided to resolder all 3 traces.
I fluxed each trace solder point and used fine ELECTRICAL solder, not plumbing solder!
I held the soldering gun on its side as there is very limited clearance and brazed each junction much more heavily than been done originally, thinking more solder at that junction might buy more long term use...time will tell!
I reassembled, the transformer, plugged it in, turned it on, and it worked like it was brand new! I called John later and thanked him for his excellent trouble shooting and fix instructions!
FYI: The MRC tech support number is: 732-225-6360
