Apple II europlus power supply is chirping and gives a fluctuating voltage output

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Joined: Aug 4 2015
Posts: 31

Symptoms:
The power supply is chirping and it doesn't give the output voltage which it is supposed to.
The output voltage is this:
pin 3: fluctuates bewtween +1 and +2,7 - should be +5
pin 4: fluctuates bewtween +1,3 and +1,9 - should be +12
pin 5: fluctuates bewtween -0,4 and -2,3 -s hould be -12
pin 6: fluctuates bewtween -4 and -8 - should be -5
I'm not an electronic Expert and I only have a simple multimeter to measure it, so it's difficult to be precise.

It's measured with power supply pulled out of the machine, so it is without any load.
(I do have another power supply that works and the output is steady with the correct voltages without any load.)

The broken power supply failed after my apple II had been sitting in a box unused for about 25 years, and it worked fine for about a week with a few hours work time each day, before it developed the fault.
When I look at the capacitors and the other components of the power supply there isn't any "smoking gun", they all look fine (to my eye).
I have changed all the electrolytic capacitors and put in new ones, including the C7, and I have also changed the 0,1 uf MP capacitor.
That changed nothing.

The power supply is the ASTEC model AA11040C 230V.

Which component should I change now?
Any advice?

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speedyG's picture
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Joined: Nov 16 2011
Posts: 2413
Re: Apple II europlus power supply is chirping and gives a ...

First: Powersupply needs loads at least at +5 Volt and +12 Volt to operate correct....
in general old harddisks serve fine as load....
Second: without measurements taken by oscilloscope changing components is just shooting with the
muskeet to the barn....
maybe understanding the functions of the supply will help to solve the problem ?
http://www.appleii-box.de/appleboxallabotpowersupplies.htm
Third: there are several dozends of former threads related to this topic here....
so a view to the right top searchfield would be next attempt....

speedyG

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Joined: Aug 4 2015
Posts: 31
Re: Apple II europlus power supply is chirping and gives a ...

Hi speedyG and thanks.
I'm not an expert at this, but I note that the webpage mentions chirping and something about a Q5 and CR19.
My power supply do not have Q5 or CR19, the closest I think would be Q4, Z1 and SCR1.
I have a schematic for the AA11040B and component listing, I can't find one for the AA11040C.
Do you know if these components are same?
They are listed as
Q4: PNP TRANSISTOR 2SB621NC
SCR1: SCR C122U/2N695
Z1: Zenerdiode 9,8V +-0,2V (2K7)
I'm having troble finding these.
Could you help with links to where I can find them?

speedyG's picture
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Joined: Nov 16 2011
Posts: 2413
Re: Apple II europlus power supply is chirping and gives a ...

i can´t see your powersupply by telepatic transmission....
how about mailing a link to a picture
with 1500 x 3000 pixel resolution ?

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In early days I had a lot of money but no time - now I have no money but a lot of time....
the second part includes less friends but a lot more joy on life....

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Joined: Aug 4 2015
Posts: 31
Re: Apple II europlus power supply is chirping and gives a ...

I put some pictures here:
http://www.tolderlund.eu/appleiips/
If you need better picture of specific areas please let me know.

The writing on Q4 transistor says:
B561
C
2C 1

The writing on the SCR1 gizmo says:
TAG P E2
2N 6395

Thanks in advance.

speedyG's picture
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Joined: Nov 16 2011
Posts: 2413
Re: Apple II europlus power supply is chirping and gives a ...

Hello Tolderlund,

inspection results to one severe fault,
1 recommended correction
and 1 inspectionpoint.

The severe fault is the missing R25 resistopr marked with purple light shading at the PCB
and in the circuitplan and layoutplan. There are still broken wires there so
i must assume that it has broken away or been cut with tweezer......
The value is 100 kiloOhm and it may be a regular 1/2 Watt resistor with 10% tolerance or less.

A well known common issue is the problem with the C7 electrolytic capacitor.
Apple populated that capacitor with 10 Volt limit - but it is strong recommended to use a
electrolytic capacitor with limit of at least 16 Volt better even 25 Volt but not higher.
It often leads to false feedback issues ( indicated by that chirping sound ).

The third point is a question:
Up to my feeling that wire inside of the fuse looks very thin and not that strong to be
used for 2,5 Ampere...... I´d guess it only to be capable of about 1 Ampere...
Please inspect the imprint of that fuse at one of the metal toppings ....
it should read 250 Volt / 2,5 A.
If not it´s recommended to replace with correct value.

And please remember testing is only valid with load at +5 Volt and + 12 Volt !
A old harddisk would serve excellent as load.

If you don´t know about pinout of the harddisk google it by pictures....
there are plenty pictures out there displaying the powerconnector pinout of harddisks....

below are the pictures from the PCB to locate the mentioned parts.

this is the layoutplan of the powersupply.
Allthough it´s from the B-Version there have not been many changes in the layout ....
only some parts have changed and the related values of some parts...

and similar is valid to the circuitplan..... B-Version and C-Version are nearly same ...
only few parts changed with values...

I hope this should solve your problems....
just give here feedback of the result....

sincerely speedyG

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In early days I had a lot of money but no time - now I have no money but a lot of time....
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Posts: 31
Re: Apple II europlus power supply is chirping and gives a ...

Hi speedyG

The fuse is the original when I got my Apple II 30+ years ago and it says 2,5A 250V.

The C7 capacitor is a new 220uf 16V. The original was also a 16V, even though the specs says 10V.
The old capacitor does look different from the rest, so maybe it has been replaced before I got the Apple. I don't know, just guessing.

The only thing I have done now, is putting in a new 100K resistor at R25.
The power supply is now working!
No more chirping and my Apple II is running again.

Here is the strange thing:
I only took the power supply apart because it stopped working and began chirping.
And I'm quite sure that I have not removed the R25.
So I just don't know why it was missing.
But the legs from it was in the holes in the PCB (you can see them in picture 5).
Can a resistor explode or vanish into thin air?
Very strange!

Anyways, the power supply is now working again.
I just need to test it for a long period, once I get the keyboard encoder board fixed (another post in this forum).

Thank you very much speedyG!
You are God!

Many regards,
Finn Tolderlund

speedyG's picture
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Posts: 2413
Re: Apple II europlus power supply is chirping and gives a ...

Happy to hear it´s back to duty again....
not God, but experience from repair of several hundreds of Apple computers back in the eighties....
and just like i said.... sometimes pictures really help detecting trouble....
after replacing all capacitors that powersupply should serve again for next 20 years...
speedyG

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In early days I had a lot of money but no time - now I have no money but a lot of time....
the second part includes less friends but a lot more joy on life....