PCB mounted transformer

[Gareth Ingram]

Hi everyone...
Need help in being able to source a replacement part from a power PCB.
The board has been removed from an item that was dropped, and the transformed snapped off the PCB.

It's simply marked as being an AC Adapter, with an input (pin 1 - 5 ) being 220v, and output (pin 6 - 7) 12V 1.5W (pin 9 - 10) 24v 3.5W (pin 12 - 13) 12V 5W

I've had a look around any sites that I know of, including RS and rapid, but can only find transformers with a single output, or double output with the same voltage. I'm probably looking in the wrong place!

I've included pictures of the damaged component, and the PCB that it was removed from (with the remainder of the component still attached).

I'll probably end up ordering a new complete board from the manufacturer (provided that it's available), but it would obviously be much cheaper (and more satisfying) to be able to repair this.

Many thanks in advance.

 

[Arouse1973]

Hello Gareth. Welcome to EP.

The transformer is more than likely a custom transformer they had made. The chances of finding another one with the same winding voltages, wattage and pin configuration is going to be difficult.

One option is to try and find a schematic of the PCB you have and hope there is a BOM with a part number attached which will give you a chance to find another transformer.

If you can't find a transformer with the correct pinouts and voltages then you could always make your own 24 Volt PSU or buy one and use a couple of 12 Volt regulators to power the 12 Volt rails and hard wire it to the pins on the circuit board. Not ideal I know.

Thanks
Adam

 

[Gareth Ingram]

Hi Adam,
Many thanks for your reply.
The company in question want £90 for a replacement PCB (which I think is a bit steep), so I've ordered in a 24V 2A psu which should be more than enough to power everything comfortably. Hopefully I can get it to fit into the casing.

As there are two separate 12v lines feeding out of the transformer (around 150mA and 300mA), should I keep these separate by running them from two 12v regulators? I assume they are separate on the power pcb for a reason!
The other 24v supply is a little confusing. It feeds to a rectifier, smoothing capacitor (1000uF), then the ground feeds to the 24v output connector. The return feed on the connector runs to three .5w 270ohm resistors in parallel, and on to the positive side of the capacitor. I don't know a big lot about power circuits, so am a bit puzzled as to what purpose the resistors could be serving? Should I just remove the regulator and capacitor, and feed my 24v line in there?

 

[Arouse1973]

Hi Gareth

I would keep the two regulators separate. You will most definitely need a heat sink if you are going to use a linear regulator. You can buy switch mode regulators and what you would need is called a buck converter, they can be a bit noisy so a simple LC filter usually sorts this if the noise is a problem.

You can pick up cheap ones online from say Amazon.

You will need to either bypass the bridge rectifiers and connect direct to the power rails otherwise you will loose voltage across the diodes.

Not sure what you mean by the return having resistors but the GND goes to the connector. If the resistors are in series with the power connections they will be for current limiting for some reason. It's hard to say without a circuit diagram.

Thanks
Adam