Re: Using a US Lisa in the UK -- redux!

Hi Tom,

I just read your post about the 60 Hz problem and that you'll intend to buy a 230-to-115 V transformer.

So just for your information one thing will be left to say or better to explain:
An Apple Lisa is totally supplied by the PSU. There is no additional connection to the external high power 115V or 230V. The first step the PSU manages is to rectify the AC-Power of 115V or 230V to a DC-Voltage of roundabout 170V up to 260V (depends on how much current the PSU is ordered to give). Second this DC-Power ist now supplied to the coil (a kind of transformer) in the middle of the board of the PSU. Two transistors are doing this work alternating by switching on and of. That's the reason, why this unit is called Power Switching Unit, PSU. They are drive by an electronic board mounted vertically (the 1.8A PSU) or by an electronic you can find on the board itself (the 1.2A PSU). This electronic is called the voltage regulation unit. You can compare this with a 18V-driller or an electric vehicle. If you push the power button more or less you will hear a humming sound with variable frequency dependeing how much power you give by pushing the button. Third, the coil has got severeal secondary outputs. The voltages were rectified and then stabilized, so that you'll get +5V, -5V, +12V and +33V, but also roundabout 170V for the CRT. Fourth, those voltages are now availlable for the different boards and units of an Apple Lisa.

That's how it works. Simply as that.

As the AC-Power is rectified it's not important whether AC frequency is 50Hz or 60Hz.
There is a suppression unit built in in the PSUs, which works perfect in 50Hz systems but not so perfect, when using it on 60Hz and conversely. But don't mind, that's not a really big problem. That's only built in to keep the power-net free from high frequency peaks, which can interfere with transistor radios or tvs. I've never seen such interferences or heard them in the radio when working with a Lisa.

By the way, japanese Lisa-users also weren't bothered by such interferences. I never heard about it. You're right, they never sold plenty of Lisas in Tokyo, but there are a lot of collectors in Japan. Greetings to the most famous of all: momo-chan. Perhaps he still reads the LisaList.

greetings TOM from Bavaria, the center of Europe, the country of the Alps, the marvellous castles of Koenig Ludwig and last but not least: The original Octoberfest

Am 12.12.2015 um 01:23 schrieb Tom Stepleton:

> Thanks for the thoughts everyone. Please rest assured that I have
> no intention of damaging my Lisas or myself :-)
>
> It would be great if a 240V to 120V stepdown transformer would do
> the job---and maybe it will! The one thing I'm worried about is the
> current frequency. The USA uses 60Hz, while UK wall current is at
> 50Hz.
>
> Stepdown transformers will change the voltage without trouble, but
> they can't change the frequency. Meanwhile, the data plate on the
> back of an American PSU is pretty specific:
>
> 120 VAC
> 60 Hz
> 1.2 Amp
> 150 W
>
> It could be that the PSU can handle 50 Hz and they just didn't mark
> it that way---there aren't too many places where you'll find 1x0
> VAC at 50 Hz (unless x == 0, and they didn't sell many Lisas in
> Tokyo...).
>
> So, has anyone tried running Lisas and ProFiles at 50 Hz on a 240V
> to 120V stepdown transformer? Is that something that should work at
> all?
>
>
> Other notes:
>
> The UPS idea is not a bad one, but when ordinary UPSes are plugged
> into a wall, I think they tend to emit the same line frequency as
> what comes in. Take this one for example (see the Technical
> Specifications tab)---output frequency is "sync to mains". Worst
> case, I guess I could plug the UPS into the wall to charge it up,
> then unplug it and use the computer for a little bit, I guess.
>
> There are converters that can turn 240V 50Hz to 120V 60 Hz, but if
> you want something strong enough to power a Lisa/ProFile combo, I
> think you need to spend a whole lot of money---thousands.
>
> --Tom
>

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