Discussion:
BOM for Apple IIc Plus PSU
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s***@mailtostu.com
2017-07-14 16:17:32 UTC
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The power supply is dying in my Apple IIc plus, so I'm just going to desolder the entire PCB and rebuild it. Yeah, you know, ten minute project, NOT! Lol!! I know, major pain in the rear, but what else am I going to do? There's one pot that controls voltage regulation. My 5v rail is going too low for the machine to run. Turn up the pot, and it turns up both rails simultaneously, and then my 12 is at 12.5+ to get the 5v high enough to run. Twenty minutes of use later, the 5v is low again, turn it up some more... Time to turn it off before the magic smoke comes out!

So I'm wondering if anyone has a bill of materials I can just copy and paste into mouser/digi-key, rather than spending at least a day looking up parts on my own.

Thanks,

-Stu
Michael J. Mahon
2017-07-14 16:37:02 UTC
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Post by s***@mailtostu.com
The power supply is dying in my Apple IIc plus, so I'm just going to
desolder the entire PCB and rebuild it. Yeah, you know, ten minute
project, NOT! Lol!! I know, major pain in the rear, but what else am I
going to do? There's one pot that controls voltage regulation. My 5v rail
is going too low for the machine to run. Turn up the pot, and it turns up
both rails simultaneously, and then my 12 is at 12.5+ to get the 5v high
enough to run. Twenty minutes of use later, the 5v is low again, turn it
up some more... Time to turn it off before the magic smoke comes out!
So I'm wondering if anyone has a bill of materials I can just copy and
paste into mouser/digi-key, rather than spending at least a day looking up parts on my own.
Thanks,
-Stu
That's a bit like fixing an engine by building a new one from parts!

There are at most one or two components that are at fault, and it's much
better to find and replace them.

Just desoldering components from a circuit board is a risky and error-prone
process.
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
s***@mailtostu.com
2017-07-28 21:46:51 UTC
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The idea was, instead of just replacing the particular component that failed, to replace all the components, which would include components that have reached the end of their expected lifetime, and components that have drifted out of the original tolerance specs. Every component has a rated number of hours it's expected by its manufacturer to last for. Did the capacitor blow because it's "old" or because the power going through it wasn't being regulated well enough?

If I have the components, it's easy enough for me to replace them without much of any risk of damage or errors, but I do understand that not everyone has the proper tools and soldering experience.

Checking most components requires removing them from the circuit. So why sit there and fiddle with that if I have to desolder them anyway? Might as well replace. Electrolytic capacitors can be checked using an ESR meter, if the original datasheet with the ESR spec is still available, but after all these years, the electrolytic caps are well past their useful life.
Michael J. Mahon
2017-07-28 23:34:45 UTC
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Post by s***@mailtostu.com
The idea was, instead of just replacing the particular component that
failed, to replace all the components, which would include components
that have reached the end of their expected lifetime, and components that
have drifted out of the original tolerance specs. Every component has a
rated number of hours it's expected by its manufacturer to last for. Did
the capacitor blow because it's "old" or because the power going through
it wasn't being regulated well enough?
If I have the components, it's easy enough for me to replace them without
much of any risk of damage or errors, but I do understand that not
everyone has the proper tools and soldering experience.
Checking most components requires removing them from the circuit. So why
sit there and fiddle with that if I have to desolder them anyway? Might
as well replace. Electrolytic capacitors can be checked using an ESR
meter, if the original datasheet with the ESR spec is still available,
but after all these years, the electrolytic caps are well past their useful life.
I think I see where you're coming from...

Wholesale replacement of parts is an unusual approach for which there is
little evidence of effectiveness.

The concept of "rated life" for electronic components is quite loose, for
which we have the abundant evidence of *lots* of 40-year-old equipment
working perfectly--well beyond any manufacturer specs.

The actual life of a component has everything to do with the environmental
conditions of storage and use. The Apple II design derates components
significantly, so most components are nowhere near their end-of-life. In
fact, most components have very few mechanisms of failure.

For example, two potentially significant failure mechanisms for integrated
circuits are moisture intrusion (loss of passivation/hermeticity) and
electromigration. After several years of maintaining hermeticity, leakage
is very unlikely. And the current levels used in the Apple II are so low in
comparison to the circuit feature sizes that electromigration. Similar
analysis applies to most components.

The only components with a relatively high failure rate are electrolytic
capacitors subjected to significant temperature rise (either from
environmental exposure or high ripple currents).
Clearly the power supply is such a stressful environment.

If we regularly experienced a system failing sequentially after replacing a
failed component, that would argue for being more aggressively replacing
components that are still functioning. But this is a very uncommon
experience.

In fact, it is so uncommon that technicians have uniformly concluded that
best practice is encapsulated in the saying, "If it ain't broke, don't fix
it." This reflects the widespread experience that reliability is damaged
more by unnecessary replacement than by continued use of a proven part.

I probably haven't convinced you, but that's the case against wholesale
replacement. ;-)
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
Stu M
2017-07-30 01:13:40 UTC
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Michael,

I'll lay out my concern plainly...
I've dealt with hundreds, if not thousands of modern desktop computers with destroyed motherboards due to power supply failures. Either by short circuit, or because the power supply's regulation was too far out of spec, damaging the VRM (fine voltage regulation section) of the motherboard by trying to make up too large of a variance.
Of course, the power supplies involved were total garbage, and this includes systems from all of the major manufacturers.
Unfortunately, too many times when a power supply fails in a "modern" computer, it takes the rest of the system out with it.
Simply put, I don't want to see this happen to any of my vintage computers.
Yes, back when the Apple II's were built, Apple was building things to a much higher standard of quality than many of todays electronics.
I feel that with every year that passes, that the risk of catastrophic power supply failure increases.
With next year being planned as the last year of the garage giveaway, and with eBay prices reaching astronomic levels, I'd like to do what I can to preserve what I have. I've smelled the magic smoke many times in my life, and the last place I want that coming from is one of my Apple II's.

Let me ask this; What can I do to ensure that a power supply is not on the verge of failure, putting the connected system at risk?

Do you agree with the general statement that most aluminum electrolytic capacitors at this point (~30 years) have either dried up, leaked, or otherwise not performing correctly? What other components do you feel should be checked or replaced at this point?

By the way, you were greatly missed at KFest this year!
Michael J. Mahon
2017-07-30 04:32:45 UTC
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Post by Stu M
Michael,
I'll lay out my concern plainly...
I've dealt with hundreds, if not thousands of modern desktop computers
with destroyed motherboards due to power supply failures. Either by short
circuit, or because the power supply's regulation was too far out of
spec, damaging the VRM (fine voltage regulation section) of the
motherboard by trying to make up too large of a variance.
Of course, the power supplies involved were total garbage, and this
includes systems from all of the major manufacturers.
Unfortunately, too many times when a power supply fails in a "modern"
computer, it takes the rest of the system out with it.
Simply put, I don't want to see this happen to any of my vintage computers.
Yes, back when the Apple II's were built, Apple was building things to a
much higher standard of quality than many of todays electronics.
I feel that with every year that passes, that the risk of catastrophic
power supply failure increases.
With next year being planned as the last year of the garage giveaway, and
with eBay prices reaching astronomic levels, I'd like to do what I can to
preserve what I have. I've smelled the magic smoke many times in my life,
and the last place I want that coming from is one of my Apple II's.
Let me ask this; What can I do to ensure that a power supply is not on
the verge of failure, putting the connected system at risk?
"The art of prophecy is very difficult, especially with respect to the
future." (Mark Twain)

And certainty is even harder! It's worth considering likely failure modes.


Short answer: it is highly improbable that an Apple II power supply will
put a main board at risk even when it fails.

I agree that electrolytics are the most likely to fail, and the vast
majority fail in the direction of "open"--usually by increased equivalent
series resistance. Such failures are extremely unlikely to result in damage
to the load (main board).

In fact, loss of regulation leading to significant overvoltage is the only
"risky" failure I can think of, and that would require the failure of one
of a couple of resistors or a transistor in the feedback loop (I'd have to
review the schematic to be more precise.) *And* the failure of the supply's
crowbar circuit.

The best predictor of a supply's robustness is its performance under full
(or 10% greater) dummy load. If it works for 30 minutes under load, it's
very likely to be quite trustworthy. (Shaking or banging it a bit is also
reassuring.)
Post by Stu M
Do you agree with the general statement that most aluminum electrolytic
capacitors at this point (~30 years) have either dried up, leaked, or
otherwise not performing correctly?
I think experience shows that the vast majority of those original
capacitors are still doing fine, and can probably be expected to continue
to operate satisfactorily. If one should fail, it will very likely fail
open, resulting in no damage, just incorrect operation.

What do you suppose is the probability of a new capacitor experiencing
infant mortality? Certainly greater than zero.

The Apple II supplies were designed with a crowbar circuit that shuts down
the supply in the event of overload or overvoltage, which provides
protection against the fault you're concerned about. (That's why Apple II
supplies "click" when shorted.). Of course, it's possible for the crowbar
to fail, leaving the load exposed if a second improbable failure occurs,
but now we're getting into the weeds. ;-)

Just consider all the Apple II's that have experienced power supply
failures--what fraction of those have led to consequent main board
failures? I'm sure there are a few, but consider the much larger fraction
that only required a replacement power supply. Apparently, Apple supplies
seldom fail catastrophically.
Post by Stu M
What other components do you feel should be checked or replaced at this point?
I would not replace any properly functioning component unless it showed
clear signs of degradation, say by overheating.

And I would never desolder a component in a functioning supply just to
measure it--that would only be justified by strong suspicion of its
integrity.

My first job was as a radio/TV repair technician, and that exposed me to a
lot of malfunctioning analog electronics. About 10% of the problems I saw
were the unintended consequence of an earlier repair! No intervention on a
circuit board is without some risk!

Rather than rattle you with non-zero probabilities of catastrophic failure,
I'd like to encourage you to have confidence in a well-designed system
(unlike some Chinese PC power supplies). ;-)
Post by Stu M
By the way, you were greatly missed at KFest this year!
Thank you, Stu--I really missed KFest and all the KFesters, too! ;-(
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
James Davis
2017-07-14 18:59:46 UTC
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Post by s***@mailtostu.com
The power supply is dying in my Apple IIc plus, so I'm just going to desolder the entire PCB and rebuild it. Yeah, you know, ten minute project, NOT! Lol!! I know, major pain in the rear, but what else am I going to do? There's one pot that controls voltage regulation. My 5v rail is going too low for the machine to run. Turn up the pot, and it turns up both rails simultaneously, and then my 12 is at 12.5+ to get the 5v high enough to run. Twenty minutes of use later, the 5v is low again, turn it up some more... Time to turn it off before the magic smoke comes out!
So I'm wondering if anyone has a bill of materials I can just copy and paste into mouser/digi-key, rather than spending at least a day looking up parts on my own.
Thanks,
-Stu
You might find what you are looking for in the "Apple II Family Hardware Information.pdf" <ftp://public.asimov.net/pub/apple_IIdocumentation/hardware/misc/Apple%20II%20Family%20Hardware%20Information.pdf>.
Bill Garber
2017-07-21 20:46:08 UTC
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Post by s***@mailtostu.com
The power supply is dying in my Apple IIc plus, so I'm just going to
desolder the entire PCB and rebuild it. Yeah, you know, ten minute
project, NOT! Lol!! I know, major pain in the rear, but what else am I
going to do? There's one pot that controls voltage regulation. My 5v rail
is going too low for the machine to run. Turn up the pot, and it turns up
both rails simultaneously, and then my 12 is at 12.5+ to get the 5v high
enough to run. Twenty minutes of use later, the 5v is low again, turn it
up some more... Time to turn it off before the magic smoke comes out!
So I'm wondering if anyone has a bill of materials I can just copy and
paste into mouser/digi-key, rather than spending at least a day looking up
parts on my own.
Thanks,
-Stu
You might find what you are looking for in the "Apple II Family Hardware
Information.pdf"
ftp://public.asimov.net/pub/apple_IIdocumentation/hardware/misc/Apple%20II%20Family%20Hardware%20Information.pdf
Click and nothing, due to a simple missing slash between apple_II and
documentation... This link will work...

ftp://public.asimov.net/pub/apple_II/documentation/hardware/misc/Apple%20II%20Family%20Hardware%20Information.pdf

Bill Garber * http://www.sepa-electronics.com *
James Davis
2017-07-22 00:36:56 UTC
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Post by Bill Garber
Post by s***@mailtostu.com
The power supply is dying in my Apple IIc plus, so I'm just going to
desolder the entire PCB and rebuild it. Yeah, you know, ten minute
project, NOT! Lol!! I know, major pain in the rear, but what else am I
going to do? There's one pot that controls voltage regulation. My 5v rail
is going too low for the machine to run. Turn up the pot, and it turns up
both rails simultaneously, and then my 12 is at 12.5+ to get the 5v high
enough to run. Twenty minutes of use later, the 5v is low again, turn it
up some more... Time to turn it off before the magic smoke comes out!
So I'm wondering if anyone has a bill of materials I can just copy and
paste into mouser/digi-key, rather than spending at least a day looking up
parts on my own.
Thanks,
-Stu
You might find what you are looking for in the "Apple II Family Hardware
Information.pdf"
ftp://public.asimov.net/pub/apple_IIdocumentation/hardware/misc/Apple%20II%20Family%20Hardware%20Information.pdf
Click and nothing, due to a simple missing slash between apple_II and
documentation... This link will work...
ftp://public.asimov.net/pub/apple_II/documentation/hardware/misc/Apple%20II%20Family%20Hardware%20Information.pdf
Bill Garber * http://www.sepa-electronics.com *
That sometimes happens when concatenating the site prefix address <ftp://public.asimov.net/pub/apple_II> to the site index suffix address <./documentation/hardware/misc/Apple%20II%20Family%20Hardware%20Information.pdf>. I guess I missed seeing the loss of the slash. But, I did replace all the spaces with %20s!
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