From: Macmoni <macmoni_at_email.domain.hidden>
Date: Wed, 10 Nov 2004 19:51:34 +0200

Hi Eric and Mike and everybody else with a dead switching power supply,

a few years ago a perfect engineer redraw the schematics of Lisa's PS. What a plenty work! Find out every connection and redraw a schematic !!! His name is James MacPhail (Kansas) and he mailed me those schematics to look over them, whether there were probably some mistakes... He's member of the LisaList, too. Ask him, he's the legal owner of his drawings.

If you read this mail, James, I believe you'll soon receive some mails, cause there seems to be your help needed... to get some Lisas work proper again - and greetings from Thomas (the second engineer, I hope you remember)

But back to the Power Supplies
I'm resident in europe and I'm very familiar in those PS. Often there are (one) or both Pull-Push Powertransistors on the primary side of the coil in a non-working condition: MJ 8505 or similar types if I remember right. This symptom is nearly in 9 of 10 cases the main reason for a non working PS, cause this PS hasn't a soft-start component if you plug in the device. So immediately approx 380 Volts DC at a AC 220 V supply, or 190 Volt DC at a AC 110 V suppy are availlable at the transistors Collector and will be switched into the coil to transform the power down to low level voltage. Unfortunately coils are very power consumptionable (is this the right word, I speak english, but technical english isn't my best) and so very high currents will flow at the beginning. Some transistors don't like that; what a shock after years of perfect work... sometimes too much and they die.

The rest of 10% of the cases are very different. I had failed secondary diodes, weak Caps, non-working (darlington) transistors at the Basis of the Power transistors; even a burned transformer which supplies the unit with double 15 Volt power have I seen. So you see, it's a wide range of faults, but this is "normal" for PS from the 80ies. Mostly it will be the Power transistors, i bet !

greetings from TOM of bavaria, in the center of europe; the country with the alps, the marvellous castles of Koenig Ludwig and the original octoberfest !

> original messages:

> Thanks for that, I have a 1.8amp PSU back ordered now on SunRemarketting
> (might take a while !). Does anyone know of any more sources I could
> try for a Lisa PSU ?
> Thanks once again
> Mike


> If you find a place that will fix Lisa power supplies, can you post it back
> here on the list?
> And lastly, if someone knows where the schematics are for the 1.8 amp,
> please post that here as well.
> - Eric
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Received on 2004-11-10 11:05:46

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