I contacted Whelen and they gave me a part #MPSA56RLRM AMO. I am not having any luck. Any suggestions would be greatly appreciated.

 

where I can find a replacement transformer?

Most of the time the transformer is OK. Some thing different is bad.

 

Try Prem. It may be a custom part though.
https://www.premmagnetics.com/

 

We are not told what the assembly is nor what it is for. So with that information I can suggest visiting the rplacement transformer store.
Now for a question: Why does the TS think that the transformer needs to be replaced? What tests have been done that would point to a failed transformer. AND what is that assembly?

 

Most of the time the transformer is OK. Some thing different is bad.

It's not for the device in the picture. It's for an identical device that had a major malfunction and burned the input components just beside the transformer. I have replaced all the burned components, but when I power it up you can hear the transformer "screeching" at between 9 and 11 VDC. When I increase the voltage to 12VDC, It completely shuts down. The transformer is the only thing left. I figured some of the insulation on the windings got hot and melted off.

 

We lack information, but by looking at the picture, ( not for the device in the picture ) it is a switching power supply, not 60hz powerline. There is no transformer store, and most likely it is custom made for this application. Some one like Prem can make one or sale you the parts to make one but they would need to know many things. If you had a really accurate schematic and time to reverse engineer it, then maybe.

 

OK, so the device must be some sort of inverter, or possibly an electronic siren driver.
So if the failed transformer can be disassembled, it might be that it can be rewound. Rewinding transformers is possible if the plastic bobbin is not melted.
So the first step is to unsolder the failed transformer from the circuit board and examine it for any signs of the plastic bobbin having melted. Then investigate removing the laminations carefully so that they are not bent and the plastic bobbin is not cracked.
At this point you should be able to compare the terminal resistance of the filed transformer to the one in the board that still works. That should tell you what winding needs replacement.

 

Are you sure the transformer is doing the "screeching"? Transformers are not designed to emit sound. Even a faulty transformer should not emit "screeching". Failed transformers usually emit magic smoke.

 

Certainly excessive currents can make transformers emit sounds. As this is not a 60 Hz mains transformer the pitch will be much higher.
So what sort of device is this PCB? I am guessing an electronic siren driver. I think that is a product that Whelen makes.

 

Certainly excessive currents can make transformers emit sounds. As this is not a 60 Hz mains transformer the pitch will be much higher.
So what sort of device is this PCB? I am guessing an electronic siren driver. I think that is a product that Whelen makes.

It is a xenon strobe light that uses 12 VDC as the input. It is using a MOSFET to drive the transformer to produce the high voltage (~400VDC).

 

OK, that is quite a bit of information that can be useful. So the transformer is an oscillator and step up unit. A low voltage winding, possibly two, and a high voltage winding. This is a candidate for a rewinding, if only the low voltage part is damaged and if the low voltage windings are on the outside.
So now there is some work to do WITH THE POWER OFF! On the unit that has not been damaged, you need to measure the resistance of each of the windings, and note what pins they are.
There should be either two or three associated with the high voltage circuit, and either 3 or four associated with the low voltage part. There should not be any connection between the two sets of terminals.
Now we need to know how fried the failed transformer is, a picture or two will be good.