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One step forward, one step back

ahm

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Joined
Apr 4, 2004
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Location
New Jersey
I got an Apple ][+ off Freecycle a while ago.
I'm totally stoked, because the ][+ was my first home computer.
The guy I got it from told me "I hope you can get it to work right".
These machines are fairly simple, so really, how much can go wrong?

Seems to power up okay, but after being on for a while, double-quote characters
begin to appear in random places on the screen. Must be flaky RAM.
So I start shuffling RAM chips around so eventually I have the first 16K bank
populated with chips that previously had been in the second bank.
Power up, write a short program, let it run for a while and problem appears to be solved. Yay! :eek:

As I'm deciding where to buy a new set of 4116 chips,
I hear a faint cracking sound and notice some white smoke begin to waft
out of the power supply. Oh well. Guess I'm done for today. :(
 
4116s are nasty little beasts. The original PC 5150 uses them too.

I remember seeing a not-too-difficult conversion to 4164 chips. Even if you don't use all of their capacity, you are doing far better than what you have now in terms of reliability and power draw.
 
But the damage is done.
I have to figure out what happened to the power supply and then fix it.
 
I hear a faint cracking sound and notice some white smoke begin to waft
out of the power supply. Oh well. Guess I'm done for today. :(

Probably just a capacitor. Might be easy to fix. The faulty component should be easy to recognise at least. The hardest thing may be to get into the power supply to replace it. I haven't checked my own Apple II+, but some of these PSUs are riveted shut.

Tez
 
The hardest thing may be to get into the power supply to replace it. I haven't checked my own Apple II+, but some of these PSUs are riveted shut.
Then I guess I was lucky. Mine opened easily enough; just 8 small screws.
But I don't see any obvious failed components.
I may have pulled the plug too soon. :D
 
Sometimes, it's just years of accumulated dust and crap burning off the components that heat up.

I had the same thing happen one day with my Apple ///, shut it off when I saw/smelled the "smoke", ripped out the supply, hosed it off with component cleaner, checked every component in it for damage and function. After all that work, I found nothing wrong, put it back together, turned it on and it's worked fine ever since.
 
I've had a few of those mains filter capacitors blow. I think standing for years lets damp get in. The mains here is 240V and to be honest I've just switch old PSU on. Not the best thing to do. I just can't be bothered in using a step down transformer and gradually increasing the volts. The capacitors are easy to replace, and they do go sooner or later. The worst part is getting the board out.
 
Remove the screws, drill out the rivets, and pop the cover off the supply. There are 2 different types of supplies used in the older Apple II/+/e computers. One is an Astec and the other is a no-name one.

Look in next to the power transformer for some small capacitors. Replace them. (Don't mistake the small green stand up coil for a cap!!! It doesn't need replacing) Next look for a power resistor in that area that is discolored. Replace it.

Those are the 2 most common parts to fail.

If the fuse is blown then check the bridge rectifier to see if it's shorted between 2 legs. It's the next most common part to fail.

Beyond that, you are down into the weeds of power supply troubleshooting. I have a thread over here: http://newlifegames.net/nlg/index.php?topic=23.0 on how you can break a switching power supply down into sections for troubleshooting.

If you give up, I have a spare supply over here that has had the cap/resistor replaced already that I'd let go for $20 shipped.

RJ
 
If you still haven't found the bad component. You could try switching on with the cover off. Don't put your head over the PSU just in case something blows, but if its a smoker you may get in indication. The filter capacitor is usually near the mains power connector, and is at least 250VAC working.
 
I forgot to say... BE CAREFUL.

If the fuse is good and if the power supply is NOT the Astec model then it will NOT have bleeder resistors on the main filter caps. Those caps WILL hold a charge for a long time and WILL shock the crap out of you with 250+ volts of DC power.

DC power causes muscles to clamp down which keeps you from releasing the power supply board you just picked up. I did that ONCE. Just ONCE. Learned my lesson the hard way.

The Astec supply has 150K 1/2w bleeder resistors across the caps to discharge them when the power is disconnected. It's a much safer design.
 
Don't worry. I'm not thrilled with poking around inside power supplies anyway.

I'm pretty sure mine is an Astec, at least that's what I saw silk-screened on the short side of the circuit board.

I won't have time to mess with it for at least a couple of weeks, so I've put everything back together and laid it aside.

Thanks for the info,
Andy
 
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