Re: Apple Lisa UK power supply

From: tommoni <tommoni_at_email.domain.hidden>
Date: Fri, 12 Oct 2007 09:14:02 +0200

hi there!

I read that conversation, which started a few days before. I'm from germany, well exactly from southern germany: bavaria and it seems to me, that your ps has been repaired in the past, when looking at your pictures, showing the black-brown overheated section of the board near the transformator-coil. The cap near the power-input is not (really) neccessary if I remember right :-) the unit's proper work won't be affected if you don't replace it, but you should do it, of course! There have been some units which use a serial-connection with a cap and the little transformer coil, so that could be such an type of ps and in this case you will have to replace it, to get the + 18 V voltage for the low voltage section of the regulating and switching unit.
In any case: replace the blown cap first!!! ...and of course spend the unit an fuse again - lol

If you don't succed in getting it repaired by a local electronic enthousiast or tv-repair-shop, then you can ship it to germany, I'll do that for you, cause I repaired a lot of those ps in the past.

5 errors are very likely:
a blown or shortcut rectifier (diode) in the primary-section (!!! high voltage, 400 V DC !!!) *1
a blown push-pull transistor in the primary-section (!!! high voltage, 400 V DC !!!) *2
a blown or shortcut rectifier (diode) in the secondary-section (mostly +5V circuit) *3
a bad cap (with very low capcity after years) in the secondary- section (mostly +5V or +12V) *4

*1 the ones between the two huge caps and the fuse-holder on top right of your picture stevejenner100/07AmpUkLisapowersupply1.jpg

*2 the MJ 8505, mountet on the black aluminium cooling unit left the two huge caps

*3 the black 083-004 dual diode (with the housing wich looks like a transistor) in the center bottom of your picture below the main transformer-coil

*4 all the caps below and right of the dual diode, near the 2x 22 pin connector of the board

there are often bad caps (with very low capcity after years) in the primary-section (the two huge ones) but thats very uncritical for a short timed test-period, the ps should work, even if they are really bad. I've repaired ps with totally blown caps and corroded ones from the early 80ies with the metal housing (without the black plastic- wrapping the +85-types) and the ps still worked fine with them, the error was mostly something different as stated in the list a few lines before. BUT you should replace them, of course with new ones, and with the same rating but types with 400 Volts ore more and +85 or more (perhaps they already have been changed, the two yellow 220 buttons seem very unusual to me, they are NOT original). If availlable then use min 450 V and 105 types with the same rating

... if you do some soldering
... and also replace the secondary caps too

Now the problem with the corrosion!
The Board is NOT a two layer board, which you have access to all wireings on the board.
There are two layers more!!! So if there is so bad corrosion, it's pretty hard work to trace all connections and get the broken corrodet connections fixed by wire. This may be the main reason, why your Lisa won't fire up. I would first try to get this fixed, perhaps by simply changing the board by another IO-board and see what happens. Perhaps you are the lucky guy today, and that was the error at all

I can also test your ps, if you want me to do so. I built a primitve testing circuit for that supplies a few years ago and made some measurements for James (hi, James, greetings from Thomas!) so thats no problem, if you won't find a local "freak" for soldering :-)

pleas excuse my perhaps faulty english, I'm not very familiar with technical english also
mais je parle francais, un peut...
ed anche posso comunicare con voi in italiano... og jeg snakker dansk, daus skraelinger!
und ich spreche Deutsch besser als jede andere Fremdsprache... ...for all those other people, who love Apple Lisas

greets: Tom from bavaria, the country with the alps, the marvellous castles from King Ludwig and of course the original Octoberfest in Munich

Am 10.10.2007 um 11:44 schrieb stevejenner100:

> Hello Everyone
> I recently aquired a Lisa 2 c.1983 system complete with all manuals
> and software, 2 profile drives etc.
> The Lisa is in generally really good condition except it wont power
> up. It appears to have a burst capacitor on the power supply but as

> this is a UK version is rated at 220v and 0.7 amps.

> Does anyone here know where I can get a replacement unit or how I go
> about getting it repaired in the UK.
> Any information will be really appreciated as really want to get my
> Lisa up and running again
> Thanks
> >

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