So I'm trying to fix the power supply for my espresso machine. I've determined that the transformer is likely the problem (no continuity across the primary coil). The OEM transformer (encapsulated) (Myrra 44170) is 117vAC to 9vAC with 256mA current on the secondary coil. In trying to find a suitable replacement transformer I have come across a few questions.

  1. I'm in the US and from what I've read I should be ok with 120V primary voltage, is this correct?

  2. Is it necessary for the transformer to be encapsulated? I know this was probably done for safety reasons, however the device wouldn't be left powered on.

  3. I can't seem to find a transformer available for 9vAC with the current around 256mA.

I was able to find one that seems like a suitable transformer (120vAC - 9vAC @ 500mA ventilated) would this work for my application? I'm just getting into electronics and electrical engineering so any advice would be greatly appreciated. Also if the replacement transformer mentioned isn't compatible could someone please provide a link to purchase one that is? I've attempted to scour the internet and am having very little luck finding 120 - 9vAC transformers that are in stock.

  • \$\begingroup\$ Depends on what’s connected downstream. With 500 mA rating, the secondary voltage will be higher that 9 V at a fraction of max rated current. \$\endgroup\$
    – winny
    Commented May 31, 2021 at 19:05

1 Answer 1


NOTE: Line-operated appliances have lethal voltages inside. No warranties expressed or implied ...

The original transformer almost certainly is a custom part designed for that appliance. Almost anything that meets or exceeds its specs will work - electrically.

The 117 Vac primary can be anything from 110 - 125 Vac.

The secondary current can be almost anything that is equal to or exceeds the current needed. That said, current = size, so a 2 A transformer will work, but might not fit.

The encapsulation has nothing to do with the transformer's electrical performance. It is a safety measure, probably because the appliance has water in it. How you deal with that is entirely up to you.

  • \$\begingroup\$ Got it. Thank you very much. \$\endgroup\$
    – Alex Katz
    Commented Jun 1, 2021 at 1:48

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