Re: Non-working Lisa PSU

[macmoni]

Hi Philip

you wrote about your problem with the PSU:
When it arrived in Japan (100v vs US120v), It worked. Sporadically and 
briefly.
Now when I use the 1.2 amp PSU and push the power button, there is a 
chirp. Actually 2 chirps, one when you push in, and the other when you 
release the power button. Chirp Chirp!
This is a very common error. The sound comes from the primary 
regulation, which tries to cut the DC power with several kHz to feed 
the transformer-coil with energy.


The main errors are:
Too high current consumption of the device(s) which are connected to 
the PSU
Very likely, if we remember, that you changed the PSU with the 1.8 type 
and got identical error-results


or

an internal problem of the PSU:
very very often the Dual-Diode, which rectifies the secondary +5V part
or
often one of the diodes, which rectifies the secondary +12V or -12V or 
-5V

or
sometimes a soon dying transistor on the primary-side (one of two of 
the pull or push circuit)

or
very rare but not least a dry cap at +5V, +12V, -5V or -12V (usually 
2200 microfarad 16V)


All errors are listed in the order you should check it. The most likely 
ones first.
BUT do that only if you are familiar with electronic components. DANGER 
risk of life !
And don't do that work alone - in order somebody can help you or call a 
medic, if you tried what will happen if several hundreds of volts bite 
you :-)

So better go to a radio or TV-expert, he will manage that very easy

greetings TOM from Bavaria, the center of europe, the marvellous 
castles of Koenig Ludwig e.g. Neuschwanstein and last but not least the 
original Oktoberfest !



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Re: Non-working Lisa PSU

[Jason Perkins]

Phil

Before I replaced the dual diode in my PSU, the power button would produce a 
pop from the speaker, and that was it. The dual diode is down in the bottom 
left corner in this pic:


http://compu85.homeip.net/stuff/Lisa/Power%20Supply/S3600129.JPG

The one I replaced it with isn't in the same packageing, so it hangs in the 
air with the heatsink attached to it.


-J 


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Re: Non-working Lisa PSU

[Philip Lord]

when you opened the PSU, did you before check, whether it's  
necessary to solder something inside?
No, I just opened and tightened/crimped the back of one of the Pots  
(using some pliers) that had come loose, and was wobbling. Did the  
trick.


What means: "a 1.2 (not working 95% of the time)" Did you ever try  
to figure out, why it works 5% ? And what did you change, so that  
it works, and what, so it doesn't work again?


When I got the lisa from Jerry, we both suspected a bad PSU. Jerry  
had not been able to get it to power on at all. When it arrived in  
Japan (100v vs US120v), It worked. Sporadically and briefly.
Now when I use the 1.2 amp PSU and push the power button, there is a  
chirp. Actually 2 chirps, one when you push in, and the other when  
you release the power button. Chirp Chirp!




...and by the way... Jason wrote: "The dual diode ended up being  
busted."
That is the reason of more than 60% of all non-working Lisa-PSU,  
cause this part is highly critical compared to the caps in the PSU


Interesting

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Re: Non-working Lisa PSU

[macmoni]

Hi Phil,

when you opened the PSU, did you before check, whether it's necessary 
to solder something inside?
It's very likely, that your PSU still works - and I'm shure it does, 
until I see one reason for an error, that it doesn't.
Yes, it's true that sometimes caps dry out and sometimes the surge 
protector cap from interference suppression gets small cracks

BUT
I repaired more than 50 PSU from Lisa over years and only one had a 
cracked cap and only two of them had a critical decrease in value due 
to "drying-out"
You must know, that the components in those PSU are NOT very critical. 
This will work proper within a wide range of values.
NB: In former times those caps even haven't been manufactured with 
exact values. There was very often a tolerance of +/- 20% at brandnew 
caps (20years ago)


So go on precisely with error-detection instead of change a lot of 
components and hope one of that had caused the error.
Perhaps you describe, what your 1,2 PSU does or doesn't do anymore to 
shrink the numbers of possible errors :-)


What means: "a 1.2 (not working 95% of the time)" Did you ever try to 
figure out, why it works 5% ? And what did you change, so that it 
works, and what, so it doesn't work again?


...and by the way... Jason wrote: "The dual diode ended up being 
busted."
That is the reason of more than 60% of all non-working Lisa-PSU, cause 
this part is highly critical compared to the caps in the PSU


greetings TOM from Bavaria, the center of europe, the marvellous 
castles of Koenig Ludwig e.g. Neuschwanstein and last but not least the 
original Oktoberfest !



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