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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I discovered that someone apparently had already gotten into the inside the shell, as the security screws had been replaced by Phillips head screws which made taking the shell apart easy.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

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This a common problem with these transformers. Both of mine, the PP and PP Dual had this failure. I bought extra contacts last time. This is a cost cutting issue. High current switches are expensive in comparison the the set up used in the PP transformers. The good news is that MRC keeps spares and they are very helpful with issues that arise with their products. These transformers are great other than the copper tabs.

No, the seller did not report any issue with the AH501, and it worked for a couple of weeks after I received it. I did quite a bit of directional testing on the engine and whistle testing on the tender, so I had used it extensively and the heavy use was probably the straw the broke the camel’s back.

From the outset the buttons didn’t seem to have quite the right feel,  but in all fairness, the seller may not have known.
I didn’t realize that the “softness” or lack of contact feeling was probably a predictor of the failure...I’ll know the next time.

Yesterday afternoon I was sooo close to taking this transformer to our county recycling center...but I thought better of it and did a last ditch bit more research. So glad I did...it saved a $147 purchase!!! And “John“ at MRC was great in talking me through the trouble shooting and fix!

I recently just got one of the AH501 units and it won't enter short circuit/overload and will basically weld the track whatever metal it is. I got a few burn spot on the track now after testing, then eventually just sticking the wires together to simulate instead of continuing to ruin the track. Does anyone have any ideas or would I be out of luck and just move onto a new power supply? I'm pretty stumped and don't want to hurt myself or the trains.

Does the "overload" light come on eventually? The output is least 7A.
I am not entirely familiar with the AH501, but the transformer is not electronically controlled or limited like the CW80. Indeed, it probably has a self-resetting thermal breaker like a postwar transformer.

Thanks for the reply. I think it was user error to be honest lol. I got it on ebay for a steal without being tested but it looked almost brand now so I figure I would gamble.

I think my noobiness to this hobby got the best of me this round. I was already calling on Saint GRJ and think it was a combo over being overtired and frustrated post holiday madness. I really was ready to relist this unit on the bay and buy the GW-180.

For my test I was trying to short 14 AWG copper stranded and finally got the "overload" light to come on which led me to believe it was maybe my fault vs the transformer. That brought me to the connections themselves. I did a really bad job connecting stuff being excited and then when I got everything connected securely, I can draw the overload light from a simple "mock derailment" vs anything wanting to continue to send power and weld the rails like I was seeing.

I absolutely plan on adding an additional breaker and TVS diodes and would appreciate anyone pointing me in the right direction of what to get.

Does the "overload" light come on eventually? The output is least 7A.
I am not entirely familiar with the AH501, but the transformer is not electronically controlled or limited like the CW80. Indeed, it probably has a self-resetting thermal breaker like a postwar transformer or the MRC TechII 027.

I didn't take any pics of the inside while working but everything looks very simple. I did see a 3amp fuse for the accessories but that was fresh.

I have the AH501 and the AH601, Dual PP. Both have circuit breakers that trip readily when an overload condition is encountered. I don't know of any internal current limiting devices in either. They are very simple devices. Mine have served me well for many years. Be careful when pressing the buttons, they aren't real switches, and they have a tendency to fail if you press them too hard with continued use.

@Mike D posted:

I have the AH501 and the AH601, Dual PP. Both have circuit breakers that trip readily when an overload condition is encountered. I don't know of any internal current limiting devices in either. They are very simple devices. Mine have served me well for many years. Be careful when pressing the buttons, they aren't real switches, and they have a tendency to fail if you press them too hard with continued use.

Thanks Mike, I appreciate that info. The buttons all work perfectly at the moment and will definitely be gentle when pressing.

@papajoewill posted:

I recently just got one of the AH501 units and it won't enter short circuit/overload and will basically weld the track whatever metal it is. I got a few burn spot on the track now after testing, then eventually just sticking the wires together to simulate instead of continuing to ruin the track. Does anyone have any ideas or would I be out of luck and just move onto a new power supply? I'm pretty stumped and don't want to hurt myself or the trains.

If you're interested in a fast acting external breaker to use with the MRC AH501 variable track output, an AirPax Instant Breaker would offer very good protection when combined with TVS diodes.  A less expensive (in the short term) solution would be an external  7.5 Amp Fast Acting fuse, with lots of spares.

The AH501 User Manual indicates this transformer is capable of 130 Watts of sustained power output.  That would suggest that it has a 7.5 Amp maximum safe operating current limit.

The

7.5 Amp   PP11-0-7.50A-OC-V   https://www.onlinecomponents.c...50aocv-10090644.html

is my recommendation.

@SteveH posted:

If you're interested in a fast acting external breaker to use with the MRC AH501 variable track output, an AirPax Instant Breaker would offer very good protection when combined with TVS diodes.  A less expensive (in the short term) solution would be an external  7.5 Amp Fast Acting fuse, with lots of spares.

The AH501 User Manual indicates this transformer is capable of 130 Watts of sustained power output.  That would suggest that it has a 7.5 Amp maximum safe operating current limit.

The

7.5 Amp   PP11-0-7.50A-OC-V   https://www.onlinecomponents.c...50aocv-10090644.html

is my recommendation.

Thanks Steve, I appreciate the recommendation a lot. I assume I would wire that Instant Breaker on the "hot wire" going to the track? I would rather do it right the first time than do any short term solution like you mentioned. Then when it is installed I am able to reset it with the switch instead of actual fuses?

As far as TVS diodes, I saw this one to be what I think I would need? part number 1.5KE33CA‎ - is it worth ordering from them for 25 shipped for $16 or go with this amazon deal?
https://www.amazon.com/20-Piec...TG9nQ2xpY2s9dHJ1ZQ==

Then because I plan to run legacy, can I still put one at the terminal post and then also the track pick ups?

Last edited by papajoewill
@Wayneas posted:

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



@Mike D posted:

I have the AH501 and the AH601, Dual PP. Both have circuit breakers that trip readily when an overload condition is encountered. I don't know of any internal current limiting devices in either. They are very simple devices. Mine have served me well for many years. Be careful when pressing the buttons, they aren't real switches, and they have a tendency to fail if you press them too hard with continued use.

Thanks for posting this information.  I have the dual version, and the power ceased to work on one side.  (Bought new about 15 years ago, has circuit breaker button, has seen moderate use.)  Awhile ago, I opened it up but couldn't see anything.  Hearing about the traces is helpful - I'll give it a look.

@papajoewill posted:

Thanks Steve, I appreciate the recommendation a lot. I assume I would wire that Instant Breaker on the "hot wire" going to the track? See diagram below.

I would rather do it right the first time than do any short term solution like you mentioned. Then when it is installed I am able to reset it with the switch instead of actual fuses?  Yes

As far as TVS diodes, I saw this one to be what I think I would need? part number 1.5KE33CA‎ -Yes this is the recommended diode

is it worth ordering from them for 25 shipped for $16 or go with this amazon deal?
https://www.amazon.com/20-Piec...TG9nQ2xpY2s9dHJ1ZQ==

Then because I plan to run legacy, can I still put one at the terminal post and then also the track pick ups?  The best places for TVS Diodes are as close as possible to the sensitive electronics you're trying to protect.

You're welcome.  See my answers above in quote box.

Here is a diagram for how to connect a breaker to a single transformer and track along with two TVS Diodes on opposite ends of the layout.  Larger layouts may benefit from additional TVS.  But, the best place for these diodes is inside the locomotives they're intended to protect.

Track Connections2a

Attachments

Images (1)
  • Track Connections2a
@Mallard4468 posted:


Thanks for posting this information.  I have the dual version, and the power ceased to work on one side.  (Bought new about 15 years ago, has circuit breaker button, has seen moderate use.)  Awhile ago, I opened it up but couldn't see anything.  Hearing about the traces is helpful - I'll give it a look.

Take the small board under the pushbuttons off and check the copper clad tabs. This is the usual point of failure on these transformers. Both of mine had this issue. There is a big plastic block with springs in there. Be careful when removing it or you may be hunting springs. The contacts could be broken or have a failed solder joint. I got lucky on one and just had to position the contact and reflow. The other one was a contact swap. If you have to get contacts, I highly recommend getting extras.

@SteveH posted:

You're welcome.  See my answers above in quote box.

Here is a diagram for how to connect a breaker to a single transformer and track along with two TVS Diodes on opposite ends of the layout.  Larger layouts may benefit from additional TVS.  But, the best place for these diodes is inside the locomotives they're intended to protect.

Track Connections2a

That was the exact diagram I was thinking. Thank you for the reply being color coded and understandable.

Because I plan on a train shelf I will have pickups at two other locations that I can put the diodes on.

As far as inside the train itself, I have been in my LC2 Big Boy a few times and am comfortable in it. Would it be the same diode installed there? and where would I be looking to install it? I assume the power pickup area but unsure about "how" to find that inside the train.

Really appreciate you taking the time to respond to me and my questions.

@papajoewill posted:

...in my LC2 Big Boy ... Would it be the same diode installed there? Yes

...and where would I be looking to install it? I assume the power pickup area but unsure about "how" to find that inside the train.

The best place to install the TVS diode inside the locomotive is as close to where the Hot and Common wires (from the pick-up and wheels respectively) attach to the circuit board(s).  You can either visually follow the wires from the pick-up/wheels or you can use a multi-meter to check for continuity (nearly 0Ω (zero Ohms)) ; first between: 1)  the center rail pick-up roller and the circuit board, and then 2) the wheels to the common connection at the circuit board

See my answers above in quote box.

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