1980's electronic typewriter transformer bad?

[atikovi]

This is a Brother EM711 typewriter. It would randomly reboot as if you had turned the power off then on. Now it's totally dead. Took it apart and checked the transformer.

there is 120V on the black and white wires going up to the transformer, but only like 30 mV coming out on the two red wires on the left. Bad transformer? And where do I find a replacement? Found nothing by searching those numbers and have no idea what the output should be.

 

[atikovi]

Just ordered this one for under $15,

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[ZipZapOuch]

Just ordered this one for under $15,

Triad F-255X Power Transformer - PRI: 125VAC - SEC: 20VCT @ 2.0 AMP -- NIB!!! | eBay

Find many great new & used options and get the best deals for Triad F-255X Power Transformer - PRI: 125VAC - SEC: 20VCT @ 2.0 AMP -- NIB!!! at the best online prices at eBay! Free shipping for many products!

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I would have just ordered a 28-36v DC power supply brick.

https://www.digikey.com/en/products/detail/mean-well-usa-inc/OWA-60U-30/7705515?s=N4IgjCBcoCwBxVAYygMwIYBsDOBTANCAPZQDa4AnAOwDMVADCIWHDAKwULMBsbc3AJhABdQgAcALlBABlCQCcAlgDsA5iAC%2BhNlUQgUkDDgLEyIGizBU2Tc5apc7cFkNEhJ0uUrWbCMKjB6BkZ4hCSQ5DQ0MPQCruJSkLIKKupa4GACjND6aFihphHg3NYUgW4eSV6pvuB03EF5xmFmNBwBNoQ0cPTwDRWJyd5phAC0FI2QCgCuJuHkEMLpo0I5BjNzZjZLYxBrTQXz4PwNhAJg9DQiGjdAA

 

[atikovi]

I would have just ordered a 28-36v DC power supply brick.

https://www.digikey.com/en/products/detail/mean-well-usa-inc/OWA-60U-30/7705515?s=N4IgjCBcoCwBxVAYygMwIYBsDOBTANCAPZQDa4AnAOwDMVADCIWHDAKwULMBsbc3AJhABdQgAcALlBABlCQCcAlgDsA5iAC%2BhNlUQgUkDDgLEyIGizBU2Tc5apc7cFkNEhJ0uUrWbCMKjB6BkZ4hCSQ5DQ0MPQCruJSkLIKKupa4GACjND6aFihphHg3NYUgW4eSV6pvuB03EF5xmFmNBwBNoQ0cPTwDRWJyd5phAC0FI2QCgCuJuHkEMLpo0I5BjNzZjZLYxBrTQXz4PwNhAJg9DQiGjdAA

That's not going to fit where the transformer is located.

 

[ZipZapOuch]

That's not going to fit where the transformer is located.

That's why you'd add a 5.5x2.1mm barrel connector and leave the brick outside your typewriter. Then you don't need to worry about an expensive and large capacitor. You can likely eliminate it or replace it with a much smaller one when needed.

 

[For The Popcorn]

Hmmm. I'm counting on my fingers and I'm no accountant but:

Transformer: $15
+
Cap, 10000uf, <$10
50 volts*

Seems to be less than:

Digikey DC Supply: $33

and it preserves the original one piece operation of the typewriter.

* may or may not need replacement at some point.

 

[ZipZapOuch]

Hmmm. I'm counting on my fingers and I'm no accountant but:

Transformer: $15
+
Cap, 10000uf, <$10
50 volts*

Seems to be less than:

Digikey DC Supply: $33

and it preserves the original one piece operation of the typewriter.

* may or may not need replacement at some point.

And with the brick, you get all the short-circuit interruption and voltage surge protection of a modern power supply. User's choice. Dollars aren't everything. It's the same advice as I gave in post #30. Cheers.

 

[atikovi]

I'm not about to re-engineer a typewriter that I may use less than 15 minutes a month. The transformer is the only thing wrong with it.

 

[For The Popcorn]

You're saying it worked fine for 40 years, so you'll trust the original design? Excellent call.

 

[atikovi]

One part failed in 40 years. That's pretty good in my book. If cars were that trouble free, car makers would be out of business.

 

[Lightium]

Where's the fuse? Limit the current of the transformer to not brake the fuse.

Oh, I see you found a transformer, good.

 

[atikovi]

New transformer installed and typewriter working again. The no load output showed 23 volts. Not sure if that's bad, but nothing was smoking, yet.

 

[For The Popcorn]

The proof is that it works! Good job!

 

[ZipZapOuch]

New transformer installed and typewriter working again. The no load output showed 23 volts. Not sure if that's bad, but nothing was smoking, yet.

View attachment 145759

Let it run for a while and feel those aluminum heat sinks - can you keep your fingers on them?

 

[Nigel Goodwin]

Let it run for a while and feel those aluminum heat sinks - can you keep your fingers on them?

And lick your finger before you touch them

You should always do this, as if it's hot you will instantly hear the saliva 'boiling' - so can remove your finger before it's burnt. With a dry finger, if it's hot, your finger burns before you can feel the heat - the bodies heat sensing is a very slow action.